15 Hoa hoc lap the

TRNG I HC S PHM TP. H CH MINH ( KHOA HA )

HA HC LP TH

V TH THU HNG

TP. H CH MINH-2002

http://hhud.tvu.edu.vn

MC LC

Phn A: L thuyt

Chng 1: Khi nim c bn..........................................5

Chng 2: ng phn quang hc ..................................17

Chng 3: ng phn hnh hc.....................................38

Chng 4: ng phn cu trng ca hp cht khng vng

.....................................................................50

Chng 5: Cu trng ca hp cht vng no ..................62

Chng 6: Ha lp th ca d t v Polymer.................92

Chng 7: Ha lp th ng.........................................113

Phn B Bi tp

ng phn quang hc .................................128

ng phn hnh hc....................................132

ng phn cu trng...................................135

Phn ng th SN ............................................................... 138

Phn ng tch .............................................141

Phn ng cng ............................................144

Ti liu tham kho..........................................................148


LI NI U

Ho hc lp th (Stereochemistry) l mt khoa hc nghin cu v cu trc khng gian ca vt cht v nh hng ca cu trc ny n tnh cht ca chng.

Ho hc lp th c in ch ch trng n cc ng phn lp th trng thi tnh nh ng phn hnh hc, ng phn quang hc. Nhng gn y do s pht trin ca hc thuyt v cu trng (conformation) v phn gii cu trng (confornational analysis); v s tng hp nh hng lp th trong cc phn ng ho hc; v quy tc bo ton tnh i xng ca cc orbital... Cng vi s xut hin cc phng php vt l nh quang ph t ngoi, quang ph cng hng t ht nhn, nhiu x tia X, nhiu x electron.... Cc nghin cu v ha hc lp th cho ta nhiu hiu bit mi v s ph thuc ca cc tnh cht v nhng c tnh tinh vi v s phn b khng gian ca cc nguyn t trong phn t, trong vic gii thch c ch phn ng v c bit ha lp th cn gii thch c hot tnh sinh l khc nhau ca cc ng phn lp th.

Ha hc lp th ng nghin cu nhng chuyn ha cht khc nhau ca cc ng phn lp th gy nn bi cc c im cu trc khng gian ca chng nh hin tng racemic ha trong phn ng th SN1, SR, SE, s nghch chuyn cu hnh trong phn ng th SN2, s lu tr cu hnh trong phn th SNi, epimer ha trong phn ng cng AN vo hp cht carbonyl....

Nhiu cng trnh nghin cu v ha hc lp th c nh gi cao, mt s c trao gii Nobel v ha hc, phn nh vai tr tm c ca mn hc ny.

Vi tnh cht quan trng ca ha hc lp th, mt lnh vc khng th thiu c i vi ha hc hin i, nn s ra i quyn sch ny hy vng gip cc sinh vin chuyn ha


b sung kin thc v h tr cho qu trnh hc tp v nghin cu ca mnh.

Do kh nng cn nhiu hn ch nn chc chn khng th trnh nhng thiu st. Rt mong nhn c cc kin ng gp chn thnh ca qu ng nghip v bn c sch c hon chnh hn trong nhng ln ti bn sau.

Tc gi


PHN A

L THUYT

Chng 1:KHI NIM C BN

V HA HC LP TH 1. 1 1.1. Phm vi nghin cu ca ha hc lp th 1.2. Lc s

1.2.1. c tnh ca hp cht trin quang 1.2.2. Thuyt carbon t din 1.2.3. ng phn hnh hc 1.2.4. ng phn quang hc 1.2.5. ng phn cu trng (ng phn quay)

1.3. Cch biu din nguyn t carbon t din. 1.3.1. Cng thc chiu hp cht c mt nguyn t C 1.3.2. Cng thc chiu hp cht c hai nguyn t C

1.3.2.1. Cng thc tam th nguyn 1.3.2.2. Cng thc phi cnh 1.3.2.3. Cng thc Newman 1.3.2.4. Cng thc Fischer

1.4. Cu hnh tng i v cu hnh tuyt i 1.5. Danh php cu hnh

1.5.1. Danh php D,L 1.5.2. Danh php R,S 1.5.3. Danh php E,Z


1.1. PHM VI NGHIN CU CA HA HC LP TH Cng thc phng khng th m t y cc dng ca phn

t. S kho st v cc kha cnh kin trc ca phn t trong khng gian tam th nguyn rt cn thit. l phm vi nghin cu ca Ha lp th.

Mun hiu r hot tnh ca mt hp cht hu c, trc ht ngi ta phi bit cch cu to ca n v k l xc nh cu hnh ca phn t. Cu to ca phn t l trt t sp xp cc ni cc

nguyn t trong phn t. Cu hnh ca phn t l cch sp xp trong khng gian

ca nhng nguyn t (hay nhm nguyn t) quanh tm carbon i xng. Cu trng u i ca hp cht xc nh bi nh hng

cc nguyn t hoc cc nhm nguyn t gn nhau (tng tc khng ni).

Kt qu ca ni cng ha tr nh hng l s to thnh ng phn lp th gm c ng phn hnh hc v ng phn quang hc.

Ha hc lp th c in ch ch trng n cc phn t trng thi tnh lin h n cc ng phn lp th. Hin nay, ha hc lp th tr thnh mt trong nhng ti quan trng nht trong ha hc hu c l thuyt. Ha hc lp th ng kho st s tng quan khng gian gia cc nguyn t v cc nhm nguyn t chu phn ng, cng nh hng ca s sp xp trn cn bng ha hc v vn tc phn ng.

1.2. LC S 1.2.1. c tnh ca hp cht trin quang Nm 1811, Arago pht hin u tin kh nng quay mt

phng nh sng phn cc gi l tnh quang hot. Nm 1813, Biot tm thy kh nng quay mt phng nh sng phn cc tinh th thch anh. Nm 1815, Biot tm thy s quay tng t xy ra vi mt s cht lng thin nhin: tinh du thng v dung dch ca mt s cht rn (nh camphor). S khc bit quan trng gia hai d kin thc nghim va k c Biot gii thch nh sau:


OHHHOH

COOH

COOH

HOHOHH

COOH

COOH

OHHOHH

COOH

COOH(+) (-)Acid (+ -) tartric Acid meso-tartric

- Kh nng quay mt phng ca nh sng phn cc ca thch anh lin quan vi c cu c bit ca tinh th (v n mt hn khi tinh th c nu chy).

- Cn tnh quang hot ca hp cht hu c phi c lin kt vi tnh cht ca nhiu phn t ring bit (v hin tng ny c quan st trng thi lng v trng thi kh cng nh trng thi dung dch).

Nm 1821, Herschel chng minh rng mt dng ca tinh th thch anh lm quay mt phng ca nh sng phn cc theo chiu quay kim ng h, cn dng i quang (ng vi nh ca dng u trong gng phng) quay mt phng phn cc theo chiu ngc li. Nh vy nng sut quang hot lin quan mt thit vi tnh bt i xng ca tinh th.

Sau nhiu nm (1848 1853) kho st tnh quang hot ca hai acid trch t cn ru nho, Pasteur xc nhn s hin hu ca hai acid tartric: mt acid hu trin: quay mt phng ca nh sng phn cc v bn phi (acid (+) tartric) v mt acid khng quang hot (tiu trin): khng quay mt phng ca nh sng phn cc (acid () tartric). Ngoi ra, Pasteur thnh cng trong vic tch hai acid tiu trin thnh acid (+): hu trin v acid (-): t trin (quay mt phng ca nh sng phn cc v bn tri). Hai acid ny gi l hai ng phn i quang (hai ng phn i hnh). Theo Pasteur, tnh quang hot khng phi do tnh bt i xng ca tinh th m tht ra lin quan vi tnh bt i xng ca chnh cc phn t acid tartric quang hot. Sau , Pasteur cn tm thy mt acid tiu trin khc gi l acid meso-tartric. y l mt acid i xng nn khng quay mt phng ca nh sng phn cc.

Cng thc Fischer ca cc acid tartric:

Acid () tartric gm mt s bng nhau phn t i quang (c cu hnh ngc nhau) khng c tnh quang hot v l do b tr


ngoi phn t, nhng tch hai c thnh acid (+) tartric v acid (-) tartric. Acid Meso-tartric khng quang hot v kh nng quay phi ca mt nguyn t carbon bt i b hon ton cho nguyn t carbon quay tri nn acid meso-tartric cn c coi nh mt dng khng quang hot b tr ni phn t.

1.2.2. Thuyt carbon t din Nm 1858, Kekule chng minh rng trong cc hp cht hu

c, nguyn t carbon c ha tr 4, ngha l c khuynh hng to ni vi bn nguyn t hoc bn nhm. Khi nim ny rt quan trng v gip cc nh ha hc lc by gi gii thch s tng quan gia tnh quang hot v tnh bt i xng phn t.

Nm 1874, Le Bel v Vant Hoff nhn thy ng thi v c lp vi nhau rng tnh bt i xng phn t c to ra khi bn nhm khc nhau ni vi mt carbon khng phng. Chnh Vant Hoff ngh s sp xp t din ca bn ha tr ca nguyn t carbon, ngha l bn ha tr ny hng v bn nh ca mt t din vi nguyn t carbon tm ca n.

Nguyn t C t din lin kt vi bn nguyn t (hay nhm nguyn t) khc nhau gi l nguyn t bt i xng. Hu qu l hai s sp xp khc nhau c th tn ti nh vt v nh trong gng phng, khng chng ln nhau c.

Th d: Acid lactic c hai ng phn quang hc:

Acid (+) lactic Acid () lactic

Nu mt nguyn t carbon ni vi hai (hay nhiu hn) nguyn t hoc nhm nguyn t th vt v nh s chng ln nhau c v tnh quang hot mt hn.

COOH

HO

CH3

H

COOH

OH

CH3

H


ab

b

bb a

aa

cis trans

Nm 1913, Bragg chng minh c s phn b t din ca nguyn t Carbon bi nhiu x tia X ca kim cng. Nhng phng php vt l khc nh nhiu x in t v ph nghim cng xc nhn ngh ca Vant Hoff.

1.2.3. ng phn hnh hc T nm 1875, Vant Hoff ngh biu din ni i trong

etylen th abC=Cab bng m hnh hai t din chung nhau mt cnh nh sau:

Xt v mt hnh hc th bn nhm th nm trn mt mt phng. Do , s quay quanh ni i l khng cn na v s phn b ca nhm th ging nhau c th cng pha hoc khc pha ca mt phng cha ni i.

(a b)

Nm 1838, Liebig xc nh c s tn ti ca hai acid: maleic v fumaric l ng phn ca nhau.

Mi n nm 1887, Wislicenus mi chng minh rng ng

phn thc s do s hin din ca mt ni i trong phn t. ng phn hnh hc khng c nh hng trn nh sng phn cc phng, v cc phn t c ni i khng bt i xng, ngoi tr trng hp mt nhm gn trn ni i c mt nguyn t Carbon bt i xng.

a

b

a

b

b

a

a

bcis trans

HOOC

H H H

HCOOH

COOH

HOOC

acid maleic acid furamic


ng phn hnh hc thng lin quan vi cc hp cht c ni i Carbon - Carbon, hoc Carbon - Nit, hoc Nit-Nit.

Ngoi ra, cc hp cht cicloankan (vng no) cng c th c ng phn hnh hc. ng phn hnh hc dng ny thng lin quan vi ng phn quang hc.

Th d: 1,2 dimetylciclopropan c cc ng phn:

1.2.4. ng phn quang hc (xem chng 2) 1.2.5. ng phn cu trng (cu dng, quay)

Nm 1885, Baeyer xut thuyt cng cho cc hp cht vng no. Theo Baeyer, cc cicloankan c cu to l nhng a din u v phng, sc cng gc trong vng gim dn t ciclopropan n ciclopentan, ri gia tng vi cc vng ln hn. Thuyt Baeyer gii thch s tn ti cc vng nm, su cnh vi s khim din ca cc vng nh v ln hn lc by gi.

Nm 1890, Sasche cc vng c th ghnh p ng iu kin gc t din v tn ti di cu trng khng phng v khng cng. Sasche d on ciclohexan tn ti di hai dng gh v tu, tuy nhin nhng c gng u tin c lp hai dng ny u tht bi.

n nm 1911, Mohr gii thch hai dng gh v tu ca

ciclohexan bin i ln nhau d dng. Mohr cng tin on s tn ti ca decalin di hai dng cis v trans khng cng, hai dng ny c Huckel c lp vo nm 1925.

C H 3 H

C H 3 H

HCH3

CH3H

C H 3 H

HCH3

(Meso) CAP OI QUANG

* * * * *TransCis


HH

H

H

HH

H

H

H

H

HH

HH

HH

H

H

HH

1.3. CCH BIU DIN NGUYN T CARBON T DIN 1.3.1. Biu din phn t cha mt nguyn t C

biu din cng thc tam th nguyn ca phn t trn mt phng giy, ngi ta dng mt vng trn tng trng cho nguyn t Carbon nm trong mt phng, cc ni trn mt phng xut pht t mt im trong vng (m nt) v cc ni di mt phng xut pht t mt im trn vng trn (chm nt). n gin c th khng v vng trn.

Cng thc chiu Fischer ca Metan

1.3.2. Biu din phn t cha hai nguyn t C - Cng thc tam th nguyn ca Etan

- Cng thc phi cnh: nhn theo trc C C

H

CACH BIEU DIEN PHAN T METAN

HH H

H

H

H

H

HH

H

H


H H

H

H

HH

H

HH

HH

H

H

H

H

HH

H

- Cng thc chiu Newman: trc C C vung gc vi mt phng chiu, nguyn t C gn nht c biu din bng vng trn, cc lin kt vi C ny xut pht t tm vng trn.

- Cng thc chiu Fischer: mch chnh ca phn t hng theo chiu thng ng, cc lin kt hai bn l nhng lin kt hng v pha trn mt phng, cc lin kt u trn v u di l nhng lin kt hng v pha di mt phng. 1.4. CU HNH TUYT I V CU HNH TNG I

- Cu hnh tuyt i: l cu hnh thc s ca phn t trong khng gian. Danh t hu trin (quay phi) v t trin (quay tri) cho bit chiu quay ca mt phng nh sng phn cc b tc ng bi cht hu c. y l kt qu c t thc nghim, ngi ta khng th tin on dng no trong hai dng i quang ng vi dng t trin hay hu trin.

- Cu hnh tng i: Trc nm 1951, ngi ta khng c phng php no xc nh cu hnh dng hu trin hay t trin ca hai dng i quang. Tuy nhin, ngi ta c th xc nh cu hnh ca cc cht quang hot i vi nhau v i vi hp cht mu c cu hnh bit. Cu hnh ny gi l cu hnh tng i.

1.5. DANH PHP CU HNH 1.1.1. Danh php D,L

Hp cht c chn lm mu l gliceraldehid: - Cu hnh ca dng hu trin c Fischer qui nh l

D (+) gliceraldehid.


OHH

CH2OH

CHO

HOH

CH2OH

CHO

OHH

CH2OH

COOH

*OHH

CH2OH

CHO

* HgO

Acid D-(+)-gliceric Acid D-(-)-gliceric

OHH

CH3

COOH

*OHH

CH2Br

COOH

* Zn/HCl

Acid D-(-)-3-bromo-2-hidroxipropanoic Acid D-(-)-lactic

O HHHOHO HHO HH

C H 2 O H

C H O

D (+) glucoz

- Cu hnh ca dng t trin c gi l L (-) gliceraldehid.

D-(+)-gliceraldehid L-(-)-gliceraldehid K hiu: D, L l cu hnh tuyt i Du (+) hay (-) lin h n chiu quay

Qui tc Fischer c chp nhn mt cch rng ri v cc hp

cht c cu hnh lin quan n D (+) gliceraldehid i vi chiu hng ca H v OH gi l ng phn D, d chng l hu trin hay t trin.

Th d: PBr3

Trong s tng quan gia andehid D (+) gliceric vi acid D (-

) gliceric khng c phn ng no lm thay i cch sp xp bn lin kt vi nguyn t Carbon bt i xng. V th cc hp cht u c cu hnh D.

Nu phn t c nhiu nguyn t Carbon bt i xng, cu hnh ca mt tm thng c lin kt trc tip hoc gin tip vi gliceraldehid, cn cu hnh ca cc tm khc c xc nh i vi tm th nht.

Th d: glucoz trong thin nhin c cng thc:


HNH2CH2OH

COOH

NH2OHH

CH3

HCOOH

HOHOHH

CH2OH

CHO

L (-) Treonin D (-) Treonin

O HHHOH

C OO H

C OO H

Theo qui c dng cho hp cht ng, cu hnh chung ca mt phn t c xc nh bi cu hnh ca nguyn t Carbon bt i xng mang ch s cao nht vi gliceraldehid (Carbon s 5 trong glucoz). i vi ( - Aminoacid hp cht mu l L (-) Serin

Cu hnh ca cc ( - Aminoacid c nhiu nguyn t Carbon bt i xng c xc nh bi Carbon bt i xng c ch s thp nht (nguyn t Carbon ( i vi nhm COOH).

So snh trt t: lin kt ca Treonin v Treoz c s ging nhau, Treoz c cu hnh D theo qui c hp cht ng, cu hnh L theo qui c hp cht aminoacid.

S kin ny a n mt s nhm ln quan trng trong vic xc nh cu hnh cc hp cht khc ng v ( - aminoacid.

gii quyt vn ny, ngi ta dng ch g (gliceraldehid) biu th qui c ng, v ch s (Serin) biu th qui c aminoacid.

Acid Ds (+) tartric Acid Lg (+) tartric

1.5.2. Danh php R,S D (+) gliceraldehid v D (-) gliceraldehid c cu hnh ging

ht nhau nhng quay mt phng nh sng phn cc theo hai chiu ngc nhau. Nh vy, khng c mt h thc no r rt gia cu hnh ca mt hp cht v du chiu quay ca n. Mt khc, du chiu quay ca mt vi hp cht thay i theo nhit , nng , dung mi, tnh acid ca dung dch hay mui trung ha.


Mt danh php c h thng biu th cu hnh l cn thit. H thng Cahn Ingold Prelog (1956) dng ch: R (rictus: phi) v S (sinister: tri) xc nh cu hnh ca cc nguyn t bt i xng C*abcd.

- Xt th t u tin ca cc nhm (theo qui tc th t u tin) a > b > c > d.

- Nhn cch sp xp t din cc nhm a,b, c t pha xa nht i vi nhm u tin thp nht d: o Nu th t a, b, c theo chiu kim ng h th cu hnh

ca C* l R. o Nu th t a, b, c ngc chiu kim ng h th cu

hnh ca C* l S

Cu hnh R Cu hnh S

1.5.3. Danh php E,Z i vi cc anken mang cc nhm th khc nhau

Xt theo qui tc th t u tin: a>b; c>d

- E khi a, c v tr trans i vi nhau - Z khi a, c v tr cis i vi nhau

Qui tc th t u tin 1. Cc nhm u tin c sp xp theo th t gim dn s

in tch ht nhn nguyn t ca nguyn t lin kt trc tip vi C*

Th d -I > -Br > -Cl > -F -SO3H > -OH > -NH2 > -CH3

2. Nu hai nguyn t gn trn C* ging nhau th xt nguyn t lin kt trc tip vi nguyn t . Nu vn khng chn c u tin th xt tip nguyn t th ba

Th d: -CR3 > -CHR2 > -CH2R > -CH3

a

b

c

d

d

a

bc d

a

bc


CH

C

C OO

HC N

N

N

OHH

CH3

COOH

OHCH3CH2Br

CH2OH

(R) (S)

-NR2 > -NHR > -NH2 3. Mt nguyn t lin kt i hay ba tng ng vi hai

ni n hoc ba ni n vi nguyn t (ch c mt lin kt tht, lin kt cn li gi nh c u tin thp hn).

Th d: -CH=CH- tng ng vi -CHO tng ng vi -C(N tng ng vi

4. ng v c khi lng ln hn c sp xp trc: T > D > H

5. Cu hnh cis u tin hn trans; R u tin hn S Th d:

Trong cng thc Fischer, xc nh cu hnh (R,S) ta c th: - i v tr ca hai nhm gn trn mt nguyn t C* dn

n dng i quang. - V s trao i ln th hai hon li dng u. Sau khi i

lin tip hai ln cc nhm th ti mt nguyn t C* sao cho nhm c u tin thp nht xung di, ri xt chiu quay ca ba nhm cn li.

3N 2H

C OHC 3NH

C OH

HH C

O

H2H

O

( R )

OHH OHH

C O OH

C O OH

OH

OH

H

H

COOH

COOH

( R )( S )

CH 3

CH 2-CH 3H C H 3 CH 2O H

CH 2B r FCH 3

( E ) ( Z )


Chng 2: NG PHN QUANG HC 2. 1 2.1. nh sng phn cc v tnh cht ca n 2.2. Nhng cht quang hot 2.3. Phn cc k 2.4. Hp cht quang hot c hai hay nhiu Carbon bt i khc

nhau 2.5. Hp cht quang hot c hai hay nhiu Carbon bt i ging

nhau 2.6. Hp cht quang hot khng c Carbon bt i

2.6.1. Tnh bt i xng ca phn t Trung tm khng trng vt nh Tnh quang hot do c trc khng trng vt nh Tnh quang hot do c mt phng khng trng vt nh

2.6.2. Tnh c th lp th ca cc qu trnh ha sinh 2.7. Bin th RACEMIC (dng tiu trin)

2.7.1. Bn cht ca bin th Racemic 2.7.2. S to thnh bin th Racemic

2.7.2.1. Phng php trn ln 2.7.2.2. Phng php tng hp 2.7.2.3. Phng php Racemic ha

2.7.3. Tnh cht ca bin th Racemic 2.7.3.1. Hn hp Racemic 2.7.3.2. Hp cht Racemic 2.7.3.3. Dung dch Racemic rn

2.7.4. S tch ring bin th Racemic thnh cc i quang 2.7.4.1. Phng php nht ring v kt tinh t pht 2.7.4.2. Phng php ha hc 2.7.4.3. Phng php to phc phn t 2.7.4.4. Phng php sc k


( 1 )

( 3 )

(4

(2)

2.1. NH SNG PHN CC V TNH CHT Theo thuyt in t ca nh sng th nh sng t nhin (nh

sng thng) gm nhiu sng in t, c vect in hng theo tt c cc hng trong khng gian v vung gc vi phng truyn sng.

Hnh 1 S dao ng ca nh sng thng v nh

sng phn cc (1) nh sng n sc (2) Lng knh Nicol (3) nh sng phn cc (4) Mt phng phn cc

Nu cho tia nh sng t nhin qua knh lc mu to nh sng n sc (c di sng ging nhau, cng dao ng trong nhng mt phng thng gc vi phng truyn sng). Cho chm tia n sc i qua lng knh Nicol v do s b tr nht nh ca knh ny th ch c tia sng phn cc phng i qua, tia sng ny ch dao ng trong mt mt phng thng gc vi phng truyn gi l nh sng phn cc phng.

2.2. CHT QUANG HOT Nm 1813, nh vt l hc ngi Php Biot khi nghin cu s

tng tc ca nh sng phn cc vi cht pht hin trong thin nhin tn ti hai dng tinh th thch anh: mt dng lm quay mt phng ca nh sng phn cc phng sang phi v dng kia lm quay sang tri. Tng t, mt s hp cht khc: HgS, NaCl, ZnSO4 cng c c tnh trn.

n nm 1815, Biot li pht hin c rng mt s cht hu c: ng, du thng, campho, acid tartric cng lm quay mt phng dao ng ca nh sng phn cc phng v khi trong dung dch hay trng thi lng chng vn gi c tnh ny.

Do , tnh quang hot khng phi do cu trc tinh th m do cu trc ca nhng phn t ring bit. Nh vy, tnh cht lm


100 l.c

quay mt phng ca nh sng phn cc c gi l tnh quang hot v cht tng ng c gi l cht quang hot.

2.3. PHN CC K Phn cc k l dng c dng o quay cc ca cc cht

quang hot. Phn cc k gm cc b phn chnh sau:

- Lng knh Nicol c nh dng lm knh phn cc chuyn nh sng n sc chiu vo n thnh nh sng phn cc.

- Lng knh Nicol th hai dng lm knh phn tch, lng knh ny quay c, gc quay c th tnh theo thang chia .

(1) Ngun sng (5) Mt phng b quay (2) Lng knh Nicol (6) Thang chia (3) nh sng phn cc (7) Lng knh Nicol phn tch (4) ng ng cht kho st (8) Th knh

Lng knh Nicol phn tch phi c b tr sao cho khi n v tr s khng th cc trc ca nhng tinh th ca hai lng knh song song nhau. Khi , nh sng phn cc c sinh ra bi lng knh th nht d dng i qua lng knh th hai. Nh vy knh phn tch dng xc nh xem mt phng phn cc b quay i mt gc bao nhiu di nh hng ca cht kho st. t ng ng cht lng tinh khit hoc dung dch cht kho st gia knh phn tch v knh phn cc.

quay cc ring ca cht quang hot: t

[] =

(1)

(3)(4) (5)

(6)(7)

(8) (2)


l.d

. V l.a

t[] . M 100

( : gc quay o c trn my (tnh bng ) t : nhit khi o (0C) ( : di sng ca nh sng s dng ca Hg ( = 546 nm ca Na ( = 589 nm l : chiu di ca ng ng cht kho st (dm) c : s gam cht c trong 100 ml dung dch

i vi cht lng tinh khit: t

[] =

Thc t, ngi ta ha tan a gam cht vo 1 bnh nh dung tch V ml:

t [] =

Gc quay ca cht quang hot ph thuc vo:

- di sng ca nh sng phn cc (() - Nhit khi o (t0C) - Chiu di ca dng c ng cht (l) - Dung mi v nng ca dung dch (i vi dung

dch) Th d: i vi dung dch 20% trong nc ca acid (+)

tartric, o 200C, di sng D th quay cc ring: 20 [] = +11,98o D

quay cc ring ca mt cht l mt hng s, c trng cho hp cht quang hot, tng t nh nhit si, nhit nng chy c dng c trng cho hp cht hu c.

quay cc phn t gam

t [M] =

M : phn t gam ca cht quang hot


CH 3 CH

OH

COOH

OHH

CH3

COOH

HOH

CH3

COOH

Acid (R) Lactic Acid (S) Lactic

CH2OH CHOH CHOH CHO* *

OHHOHH

CH2OH

CHOHOHHOH

CH2OH

CHOOHHHOH

CH2OH

CHOHOHOHH

CH2OH

CHO

2.4. HP CHT QUANG HOT C HAI HAY NHIU CARBON BT I KHC NHAU

Rt nhiu hp cht t nhin nh: glucid, protid, steroid, ancaloid trong phn t c nhiu nguyn t C*, cho nn vic nghin cu v mt ha hc lp th nhng hp cht loi ny l rt quan trng.

Hp cht c n nguyn t C* bt i khc nhau th c: N = 2n ng phn quang hc

Th d 1: n = 1 Acid lactic c hai ng phn

quang hc lp thnh mt cp i quang :

Th d 2: n = 2 c bn ng phn quang hc Glucid tetroz (A1) (A2) (A3) (A4) (2R,3R) (2S,3S) (2R,3S) (2S,3R)

(A1) v (A2); (A3) v (A4) : cp i quang (A1) v (A3); (A1) v (A4) cp bn i quang (A2) v (A3); (A2) v (A4) (ng phn lp th dia)


H OH

CHO

H

CH2OHOH H

CHO

OHH

CH2OH

H OH

CHO

OHH

CH2OH

OH H

CHO

HHO

CH2OH

HO

ng phn eritro treo

(A1) (A2) (A3) (A4)

(A1) ; (A2) : ng phn Eritro (A3) ; (A4) : ng phn Treo

ng phn eritro: khi quay quanh trc lin kt C2*-C3*

sao cho cc cp nhm (hay nguyn t) ging nhau n v tr che khut tng i mt.

ng phn treo: cng quay tng t trn nhng khng th em cc cp nhm ging nhau n v tr che khut vi nhau cng mt lc c. ng phn lp th bn i quang cn gi l ng phn lp th khng i quang hay ng phn lp th dia.

Hin nay, khi nim ng phn lp th dia c m rng hn v bao gm hai hin tng ha hc lp th ring r nhau:

- ng phn lp th (-dia: l ng phn lp th khng i quang do c mt t hai nguyn t C* bt i tr ln; cng nh cc ng phn cis trans cc dn xut hai ln th ca vng no. - ng phn lp th (-dia: thuc loi ng phn cistrans ca hp cht c lin kt i trong phn t. Trong mi trng i xng, tnh cht ca cc ng phn i

quang l ging nhau, cn ca cc ng phn lp th khng i quang (bn i quang) th li khc nhau rt nhiu v tnh cht vt l v ha hc. Trong phn t cc cht i quang, khong cch gia cc nguyn t (hay nhm nguyn t) l ging nhau, do kh nng phn ng ca chng i vi mt tc nhn i xng l hon ton ging nhau. Nhng khi tc dng vi tc nhn bt i xng, cc i quang li c kh nng phn ng khc nhau (th d trong phn ng ha sinh thng ch c mt trong hai i quang tham gia phn ng vi enzim). iu ny gii thch s khc nhau v mi, v v hot tnh dc l ca cc i quang. Cn cc


**CHOH

HOOC CH COOH

OH

HH

COOH

COOH

OHOH

HH

COOH

COOH

OHOH

HH

COOHOH

OHCOOH

ng phn bt i quang, khong cch gia cc nguyn t (hay nhm nguyn t) khc nhau nn c s khc nhau v nhit si, nhit nng chy, tnh tan v cc c trng v ph Nng lng t do ca cc ng phn bn i quang khng ging nhau nn chng c kh nng phn ng khc nhau.

2.5. HP CHT QUANG HOT C HAI HAY NHIU CARBON BT I GING NHAU

* Hp cht c n C* ging nhau

Dng quang hot Dng meso

n = s chn 2n-1 2(n-2)/2

n = s l 2n-1 2(n-1)/2 2(n-1)/2

Th d: Acid tartric

n = 2 c hai dng quang hot v mt dng Meso

Acid Meso-tartric Acid () tatric

* Hn hp ng phn t acid (+) tartric v acid (-) tartric l mt dng khng quang hot (bin th racemic; hn hp tiu trin) l do b tr ca hai phn t i quang.

* ng phn acid meso-tartric khng quang hot do s b tr ni phn t, khng th dng phng php tch ring tch n thnh hai i quang c.

So ong phan

So nguyen t C*


HHOHOH

CO OH

CO OHCH3

CO OH

OHH

(1) (2)

Th d 2: Acid 2,3,4 - Trihidroxiglutaric (n = 3C*) c hai dng quang hot v hai dng meso

Mpx

S khc nhau v tnh cht vt l gia hai dng meso, dng

meso ( I ) d dng to thnh dng lacton (c nhit nng chy khng r) cn dng meso (II) li b nng chy (Tnc = 1520C) m khng c s thay i v mt ha hc.

Hai dng i quang (III), (IV) u c nhit nng chy bng 1280C.

Ch : C3* ch l bt i trong hp cht meso (I), (II) nn gi l C3* bt i xng gi nh.

C3 khng bt i trong hp cht (III), (IV) v cu hnh ca C2, C4 hon ton ging nhau.

2.6. HP CHT QUANG HOT KHNG C CARBON BT I

2.6.1. Tnh bt i xng ca phn t Khi nim tnh quang hot t lu gn lin vi s bt i

xng ca phn t. Vy thut ng s khng trng vt-nh (chirality) c ngha l g?

Th d: xt hai cht quang hot l acid lactic (1) v acid tartric (2)

(1) l mt phn t bt i xng (2) c trc i xng bc hai i qua tm ca phn t

(trc ny vung gc vi mt phng v) v do phn t acid

H O HH OHH

C O O HOH

C O O H

HOHHHOH

COOHOH

COOH

HHOHOHH

COOHOH

COOH

OHH OHO H H

C O O H H

C O O H (I) (II) (III) (IV) 2 dang meso 2 dang quang hoat


PCH3Ph

OCH3

SOCH3

CH3

..

tartric khng th xem l bt i xng, m l khng trng vt-nh

Do , iu kin xut hin ng phn quang hc l s bt i xng; song khng phi l iu kin cn, iu kin cn v l s khng trng vt-nh.

2.6.1.1. Trung tm khng trng vt nh Trung tm khng trng vt nh c th l C*, Si*, P*, S*

(xem cp electron t do l nhm th th t). Th d:

Acid lactic Metyl -naphtyl phenylsilan ( 1 ) ( 2 )

Metyl paratolylsulfoxit Orto-Anisylmetylphenylphosphin

( 3 ) ( 4 ) Trong hp cht (3), (4) cc nhm th xung quanh trung tm

vt khng trng vt-nh c phn b theo hnh thp, tuy nhin nhng cu trc ny c th dn n t din, nu xem cp electron t do l nhm th th t.

2.6.1.2. Tnh quang hot do c trc khng trng vt nh a ( b v c ( d

(a c th ging c v b c th ging d)

Nu trong phn t bn nhm th a, b, c v d tng i mt

phn b trn mt trc v khng nm trong cng mt mt phng, nh c biu din di dng mt t din b ko cng th xut hin tnh quang hot. Trc ca phn t nh vy gi l trc khng trng vt-nh.

* Trc khng trng vt-nh tn ti cc h:

OHH CH 3

COOHSi CH 3H

Ph*

*


BrNH2

CH3

Br

C H3NH2

COOH

HOOCNO2

O2N

COOH

HOOC

O2N

NO2

a) Cumulen: (s chn ni i nh alen) (a ( b) v (c ( d) (P) ( (Q)

ALEN b) Biphenyl: mang nhm th

ng phn khng gian do s cn quay t do xung quanh lin kt n

Acid 6,6- dinitro-biphenyl- 2,2-dicarboxilic

Trong phn t biphenyl, hai nhn benzen c th quay t do quanh trc Carbon - Carbon trung tm; nhng khi phn t c mang nhm th c kch thc ln ti cc v tr (2, 6, 2, 6) th s quay b cn tr, hai nhn benzen khng cn v tr cng phng do tr ngi lp th pht sinh t nhng nhm th c kch thc ln cc v tr orto, v th h phn t tr nn cng chc.

Thc t, ngi ta tch hai c hai dng i quang ca acid trn.

* iu kin ch yu biphenyl th c tnh quang hot l cc nhm th phi c kch thc kh ln cn tr s quay t do v mi nhn benzen phi c th khng i xng. Ngoi ra, hai nhm th orto khng cn phi gn trn hai nhn khc nhau.

Th d: 3,3- diamino - 2, 6 dibromo - 4, 4 - dimetyl biphenyl cng c tch hai.

a C C C

c

d

a

bC C C

c

d ) Q)Pb


HCH3

H COOH H

H CH3

HOOC

NHOOC

R

..NH C NH2

ON

Ph

C Ph

O

R

H

RH H

R

H

R

c) Ankiliden ciclan:

Nu thay th mt ni i trong alen bng mt vng, v mt hnh hc ca phn t khng thay i. Cc ankiliden mang nhng nhm th thch hp c th c ng phn quang hc.

Th d: vi Acid 4 - metylciclohixiliden acetic c tch hai thnh hai dng i quang :

Mt s hp cht c lin kt i C=N nh oxim, semi carbazon, phenyl hidrazon cng c tch hai, nhng cc ng phn quang hc ny khng bn v b racemic ha nhanh chng.

Dn xut ca 4 - carboxiciclohexilidenimin vi R: OH

d) Spiran: s thay th hai lin kt i trong Alen bng hai

vng dn n mt h vng c chung mt cnh (hai vng i nh): Spiran. Nu hai vng mang nhng nhm th trn hai nguyn t carbon ti hai u ca h nm trong hai mt phng thng gc vi nhau th chng c ng phn quang hc.

Th d: Acid spiro [3,3] heptan - 2, 6 - dicarboxilic v 2, 6 - diamino spiro [3,3] heptan


OO

(CH2)8

Br

H

H HH

(A) (B)(R) (S)

R = _ COOH hay _ NH2

2.6.1.3. Tnh quang hot do c mt phng khng trng vt nh

Mt phng khng trng vt-nh c cc hp cht ansa.

Th d: (A) * (R) - 14 Bromo - 1,12 - dioxa [12] paraciclofan

(B) * (E) ciclo octen u c mt phng khng trng vt-nh nm trong mt phng giy

2.6.2. Tnh c th lp th ca cc qu trnh ha sinh

Cc i quang khng khc nhau v l tnh v ha tnh thng thng nhng nhiu khi li khc nhau r rt v tc dng sinh l.

Th d: (-) Nicotin c trong thuc l c hi hn (+) Nicotin vi ln hoc cc i quang ca aminoacid c v khc nhau nh L-asparagin v L-tritophan khng c mi v, cn L-leuxin v L-Tyroxin c v ng trong khi cc ng phn D - tng hp c v ngt.

Acid L-glutamic thin nhin c v ngt, mui Natri ca acid L-glutamic l bt ngt (m chnh) dng lm gia v thc phm; cn acid D-glutamic khng c c tnh y.

Do c tc dng sinh l khc nhau, cc i quang ca nhiu hp cht c dng lm thuc cha bnh.

Th d: R (-) epinephrin thin nhin, mt hormon chnh ca tuyn thng thn. Do khi cho ngi bnh ung epinephrin tng hp, th ch R (-) epinephrin c hiu ng kch thch ging


ClCl

ClCl

Cl

Cl

CH

CCl3X X

*

nh hormon thin nhin, cn S (+) epinephrin khng c hiu ng kch thch m li gy c nh.

Tnh c th lp th cng biu hin r cc hp cht bo v thc vt. Th d trong tm ng phn ca C6H6Cl6 (6,6,6) ch c ng phn ( c hot tnh tr su mnh.

(C) (D) ng phn ( _ ca 6,6,6 (D.D.T)


Hoc khi nghin cu mt lot cc ha cht tr su v kh nng quay t do trong phn t kiu D.D.T, ngi ta nhn thy nu cc hp cht kiu (D), cc nhm th X v tr orto lm gim tnh tr su.

* Acid cis-cinamic kch thch mnh s tng trng ca cy, trong khi acid trans-cinamic li khng c hot tnh y.

Nguyn nhn ca nhng khc nhau v hot tnh sinh l l s khc nhau v cu trc khng gian (khc nhau v cu hnh) v c th gii thch nh sau:

i) Cc i quang c th c phn b khc nhau trong m t bo ca c th sng.

2i) Cc i quang c th c i lc khc nhau i vi c quan th cm (Receptor). S khc nhau ny l do vi nhng i quang no chng c kh nng tng tc c ch khng do tnh cht bt i xng.

3i) Cc enzim trong c th sng u bt i xng nn chng c kh nng phn bit cc i quang, thng thng ch mt trong hai i quang l ph hp vi tm enzim. 2.7. BIN TH RACEMIC (dng tiu trin)

2.7.1. Bn cht ca bin th racemic

Bin th racemic (dng tiu trin) l mt hn hp ng phn t (equimolar) ca hai ng phn i quang ca mt cht c phn t bt i xng. Do tr s quay cc ca tp hp ny bng khng. Thng c k hiu l () hay D,L.

2.7.2. S to thnh bin th Racemic 2.7.2.1. Phng php trn ln

Phng php n gin nht iu ch cc bin th racemic l trn k s lng ng phn t ca hai dng ng phn hu trin (quay phi) v t trin (quay tri): qu trnh ny gn lin vi s thay i Entropi bi v bin th racemic trng thi hn lon hn cc i quang ring bit.

Entropi ca s trn ln: (S = - Rx1Lnx1 = Rx2Lnx2 (bin th racemic: x1 = x2 = 1/2) ( (S = 5,8 ( J/mol. S thay i nng


CCOOH

H

CH3

H2 2+ Br2 CCOOH

H

CH3

Br + CCOOH

Br

CH3

H + 2 HBr(+) (-)

P

O

H

HH

H+ HCN

CN

HH

H

OHH

+H

NC OHH H

H

lng t do khi to thnh bin th racemic t cc i quang s l (F = - T(S = -1,755 KJ/mol nhit phng.

2.7.2.2. Phng php tng hp Bng phng php tng hp cc phn t bt i xng, ngi

ta nhn c bin th racemic nu i t cc phn t i xng ny t bin th racemic m khng dng tc nhn quang hot, xc tc hay mt tng tc vt l bt i xng no.

Acid propionic Acid () -Brompropionic

* Phn ng cng HCN v acetaldehid (CH3-CHO) cho hn

hp hai i quang vi s lng bng nhau.

2.7.2.3. Phng php racemic ha Php bin i mt dng i quang tinh khit ca mt cht

quang hot to thnh hn hp racemic tng ng gi l s racemic ha. S racemic ha c th xy ra di nh hng ca nhit, nh sng hay ha cht.

2.7.3. Tnh cht ca cc bin th racemic

Thng thng trng thi kh, lng hay dung dch, bin th racemic l hn hp (gn nh l tng) ca nhng lng bng nhau ca cc phn t i quang c tnh cht vt l (nhit si, khi lng ring, chit sut, ph hng ngoi) ging tnh cht vt l ca cc dng i quang tinh khit.

i vi trng thi rn, tnh cht ca cc (dng tiu trin) bin th racemic v cc i quang khc xa nhau do lc gia cc tinh th rt c th v rt nhy k c khi thay i mt cht v mt hnh


hc. Kt qu l trng thi rn ngi ta thng gp s khc bit v tnh cht l tng v c kh nng trong ba trng hp sau:

2.7.3.1. Hn hp racemic (racemic mixture) C trng hp l trong tinh th, mt i quang c i lc i

vi nhng phn t cng loi i quang ln hn l i vi nhng phn t ca i quang kia. Trong trng hp ny, nu s to thnh tinh th bt u t phn t ca dng (+) th ch c nhng phn t (+) s tham gia vo s ln ln v sau ca tinh th. Do tinh th v m s tng ng vi dng (+) [cng tng t nh th i vi dng (-)]. Nh vy bin th racemic l hn hp cc tinh th ca c hai dng ny. Tonng chy tan

0% 50%(+) 100%(+) 0% 50%(+) 100%(+) 100%(-) 50%(-) 0% 100%(-) 50%(-) 0%(-)

( Gin nhit nng chy v tnh tan ca hn hp racemic.)

Hn hp racemic l mt hn hp cc tinh th dng (+) v dng (-), tnh cht ca n ging tnh cht ca cc i quang tinh khit. iu th hin r nh chp tia X ca dng bt v ph hng ngoi trng thi rn.

Tuy nhin, nhit nng chy ca hn hp racemic thp hn nhit nng chy ca cc i quang tinh khit. Cn tan ca hn hp racemic th li cao hn tan ca cc i quang.

2.7.3.2. Hp cht racemic (racemic compound) Nhng phn t ca mt i quang ny thng c i lc i vi phn t

ca i quang kia ln hn l i vi nhng phn t cng loi. Trong trng hp ny cc phn t i quang ngc du c kt hp i thnh t bo c bn ca tinh th. Nh vy t bo s cha mt lng bng nhau ca cc phn t (+) v (-). Hp cht loi ny gi l hp cht racemic (thng tn ti trng thi rn). Cc hp cht racemic l nhng hp cht thc chng khc bit vi cc i quang v tnh cht vt l nh khc nhau v ph hng ngoi


trng thi rn, khc nhau v nh chp tia X dng bt, khc v nhit nng chy v tan. Tonng chy tan

0% 50%(+) 100%(+) 0% 50%(+) 100%(+) 100%(-) 50%(-) 0% 100%(-) 50%(-) 0%(-)

(Gin Tonng chy v tan ca hp cht racemic) 2.7.3.3. Dung dch racemic rn (racemic solid solution)

Cc bin th racemic (i khi trng thi rn) c c tnh cht gn nh l tng, l trng hp ch c s khc nhau rt nh v i lc gia cc phn t c cng v khc nhau v cu hnh. Trong trng hp ny, s phn b ca cc phn t trng thi rn sp xp mt cch ngu nhin to thnh dung dch racemic rn.

Cc tnh cht vt l ca dung dch racemic rn (nhit nng chy, ha tan) ging tnh cht ca cc dng i quang.

Tonng chy

0% 50%(+) 100%(+)

100%(-) 50%(-) 0% ( Gin Tonng chy ca dung dch racemic rn)

C th phn bit: hp cht racemic, hn hp racemic hay dung

dch racemic rn bng cch so snh ph hng ngoi ca n trng thi rn vi ph hng ngoi ca cc i quang. Ch c quang ph ca hp cht racemic l khc vi quang ph ca i quang.

Cng c th phn bit ba dng racemic bng cch dng gin nhit nng chy, tan hay dng phng php xc nh t bo c bn nh nhiu x tia X (t bo tinh th c bn ca hp cht racemic c cha nhng lng bng nhau ca cc phn t ca hai


dng i quang; cn ca hn hp racemic hay dung dch racemic rn ch gm cc phn t ca mt i quang m thi)

2.7.4. S tch ring bin th racemic thnh cc i quang 2.7.4.1. Phng php nht ring cc tinh th bt i xng

v kt tinh t pht i vi hn hp racemic thng tn ti cc kiu tinh th ring

bit ca dng (+) v dng (-) i xng nhau, nu kch thc ca nhng tinh th ny ln v nhn bit c bng mt thng th ta c th dng kp nht ring cc phn t c cu hnh khc nhau. Nm 1948, Pasteur l ngi u tin tch ring c tinh th D - v L - Natri amoni tartrat; chng kt tinh ring bit nhau t mt dung dch ca hn hp racemic ca hai cht i quang (t ( 270C).

a s cc bin th racemic u kt tinh thnh hp cht racemic nn ch c mt s t hp cht quang hot c tch ring bng phng php kt tinh t pht.

Gn y , ngi ta cho tp cht c ch vo dung dch kt tinh ngn cn s ln ln ca mt trong cc thnh phn hn hp racemic. Bng phng php ny, ngi ta nhn c cc aminoacid c tinh khit quang hot n 90%, v n tinh th hidrobenzoin nng 3 gam c tinh khit quang hot gn 100%.

2.7.4.2. Phng php ha hc da trn s to thnh cc ng phn lp th khng i quang (bn i quang). Da trn s sau:

D1D2 D1L1 + D2

L1D2 Khi tc dng ln bin th racemic D1L1 bng mt tc nhn

bt i xng D2 thu c hai cht mi D1D2 v L1D2 l hai ng phn bn i quang. Cc ng phn bn i quang khc nhau v: tan, p sut hi, h s hp th nn c tch ring nhau ra.

S tch ring bin th racemic qua s to thnh cc ng phn lp th bn i quang gm ba giai on:

To thnh hai ng phn bn i quang


CH3

Ph

NH2H +CH3

Ph

HNH2 + Acid (+) tartricCH3OH

Tartrat (+)(+A)

Tartrat (+) (-A)(HOOC-CHOH-CHOH-COOH)**

(+)A (-)A

Tch ring hai ng phn da vo tnh cht khc nhau. Ph v phn t ng phn lp th bn i quang tinh

khit ti to li dng i quang ban u v tc nhn bt i xng.

a) Tch ring acid Theo s

tch ring cc acid racemic thnh i quang, ta dng cc ancaloit sn c trong thin nhin nh: Bruxin, strichnin, ephedrin, quinin, cinchonin, morphin hoc cc baz tng hp nh ( - phenyl etylamin; metylamin.

b) Tch ring amin tch ring cc amin racemic ta dng tc nhn bt i xng

c tnh acid: acid tartric, acid malic, acid glutamic (acid malic: HOOC - CH2 - C*HOH - COOH)

Th d: tch ri hp cht racemic ( - phenyletylamin ta dng acid (+) tartric lm tc nhn bt i theo s :

Mui tartrat (+)(-A) tan trong CH3OH km hn mui tartrat (+)(+A) do ng phn (+)(-A) kt tinh ngay di dng tinh khit, nht l khi a vo dung dch vi tinh th mui (+)(-A) c sn lm mm kt tinh. c mui hon ton tinh khit thng phi kt tinh li mt ln trong H2O ri ph v mui ny bng dung dch kim v tch ring (-) (-phenyletylamin ra khi dung dch Natri tartrat. Bi v acid (+) tartric l mt tc nhn r

R2- R1

R3RCOO NH

- R3

+

+

R3

R2

N Cl

NH l

ket tinh muoi (+) (-)

muoi (-) (-)

+ HCl

+ HCl

R-COOH (+)

R-COOH (-)

R1R2

R1

R3

H

C phan oan

(-)R-COOH (+) R-COOH (-) + N

R1

R3(hp chat Racemic)

RCOO NH+

R2 ++

R2 R1

(+) (-) (-) (-)

(-)

(-)


CH3 CHC2H5

OH

+

O

OCO

OCH3

C HC2H5

COOHO Piridin

**

COO

C

O

O

CH3

CHC2H5

_

+ Bruxin (*)Tach 2 chat (+) va (-)

*

(+)

H.Brunxin

a tinh che

+HClCOOH

C

O

O

CH3

CHC2H5 + Bruxin.HCl

+NaOHdd +LiAlH4

COONa

COONa

+OH H

CH3

C2H5

*CH2OH

CH2OH+ OH H

CH3

C2H5

*hay

tin nn vic ti sinh tc nhn bt i xng trong trng hp ny l khng cn thit.

c) Tch ring ancol: Cc ancol racemic thng c tch ring thnh i quang

bng hai phng php sau: - Este ha ancol racemic bng acid quang hot ri tch

ring cc este bng phng php kt tinh phn on. - Este ha ancol bng diacid chuyn thnh bn este c

kh nng to mui vi cc baz quang hot. Th d: tch ring hai ng phn (+), (-) ca ru Sec-

butylic ta tin hnh theo s sau:

Ru (+)(-)


CH3O

CH3O N

O O

N

Cng thc ca Bruxin

2.7.4.3. Phng php to phc phn t

Khi ch ha bin th racemic bng tc nhn bt i m to thnh c phc tinh th th c th thu c hai phc ng phn bn i quang khc nhau v ha tan v s c mt ng phn kt ta trc. Sau ph v phc ny bng cch un nng, ha tan, bng sc k hay ch ha ha hc ta thu c mt trong hai i quang ban u.

2.7.4.4. Phng php sc k tch ring bin th racemic () X thnh hai cht i quang,

ta cho () X qua ct nhi cht hp th bt i xng (vit tt l (-) Chp), cc i quang to phc yu vi cht nhi bt i xng (nh lin kt hidro) v ta c cc phc bn i quang (-) Chp (-) X v () Chp (+) X. Nhng phc ny c tnh cht vt l khc nhau, khc nhau v nng lng lin kt, v hng s cn bng to phc, do chng c bn khc nhau, ngha l mt cht i quang (t bn vng) i qua ct nhi cht hp th bt i xng nhanh hn i quang kia v nh vy hai i quang c tch ring.

Hin nay, phng php sc k c vai tr quan trng trong vic iu ch hp cht quang hot v bao gm c ba loi: sc k lng, sc k lp mng v sc k lng cao p.


Chng 3: NG PHN HNH HC 3.1. Bn cht ca ng phn hnh hc 3.2. Hp cht c ni i Carbon - Carbon

3.2.1. Danh php 3.2.2. Hp cht c mt ni i v nhiu ni i 3.2.3. Tnh cht vt l ca ng phn hnh hc

3.2.3.1. Momen lng cc 3.2.3.2. Nhit : nng chy, si, t khi v chit sut 3.2.3.3. phn ly ca acid 3.2.3.4. Ph: t ngoi, hng ngoi, cng hng t ht

nhn 3.2.4. bn tng i v s chuyn ha tng h gia cc

ng phn hnh hc 3.3. Hp cht c ni i C=N v N=N 3.4. Hp cht vng no C


Ca

b

a

b

C

P)

Q)

3.1. BN CHT CA NG PHN HNH HC

iu kin a ( b iu kin a ( b

(Q) cha lin kt ( (P) (Q)

Theo cch gii thch hin nay th nguyn t Carbon mang

ni i trng thi lai ha sp2 ngha l ch c hai trong s ba electron p c lai ha vi electron s to thnh ba orbital lai ha sp2. Ba orbital ny nm trn cng mt mt phng, c trc i xng hp nhau nhng gc 1200. Hai nguyn t Carbon dng hai orbital sp2 xen ph ln nhau to lin kt ( (C-C) v dng cc orbital sp2 cn li xen ph vi cc orbital khc to cc lin kt ( (C-a; C-b) nm lin kt ( nm trong cng mt phng. Mi nguyn t Carbon cn li mt electron orbital 2p, chng xen ph bn vi nhau to lin kt ( vung gc vi mt phng cha cc lin kt (. Do s hnh thnh lin kt ( trit tiu s quay t do v dn n xut hin ng phn cis - trans. Cu hnh cis - trans (a ( b)

Khong cch gia cc nguyn t trong phn t (X), (Y) khc nhau rt ln, do v phng din hnh hc th (X), (Y) c hnh dng, kch thc phn t khc nhau nn i lng Entalpi t do to thnh cng khc nhau, cc hng s vt l, cc c trng v ph v cui cng l tnh cht ha hc cng khc nhau r rt.

a a

b b

a

ab

b

cis (X)

trans (Y)


N=2n

3.2. HP CHT C NI I 3.2.1. Danh php

- Nu hp cht mang mt ni i C=C, mang hai nhm hay ba nhm th khc nhau, ta dng cu hnh: CIS: ch hai nhm ging nhau ( hai nguyn t C) nm

cng mt pha i vi mt phng cha lin kt ( TRANS: ch hai nhm ging nhau nm hai pha i vi

mt phng cha lin kt (.

- Vi anken phc tp, cu hnh c chn l cu hnh ca mch Carbon lin tc di nht xuyn qua lin kt i.

(mc d c hai nhm etyl nm cng mt pha i vi mt

phng)

- Nu anken mang bn nhm th khc nhau m khng chn c mch chnh th dng danh php E-Z.

Th d: 3.2.2. Hp cht c mt v nhiu ni i Tng s ng phn hnh hc ca mt hp cht c n ni i

trong phn t l: * Hp cht bt i xng * Hp cht i xng

n = s chn N = 2n-1 + 2(n-2)/2

C H 3

H

C H 3

H

C 2H 5

H

C H 3

C 2 H 5

H

C 2H 5

CH 3

C 2H 5

H

C H 3

CH 3

Htrans but-2-en.

trans-3-metylhex-3-en. cis-3-metylhex-3-en.

cis but-2-en.

CH CH2 3

CH2CH2CH3

C H 3 C H 2

C H 3 Trans-4-etyl-3-metylhept-3-en

CC H

C C CH

Z E

CBr

Cl

3

H

Cl

Br

3

H -1-Bromo-1-cloropropen -1-Bromo-1-cloropropen


N = 2n-1 + 2(n-1)/2

H

H

C2H5CH3

HH

H

C2H5

HH

HCH3

cis - 2 - trans - 4 trans - 2 - cis - 4

C C CCa a

bb

n = s l

Th d 1: hepta-2,4-dien CH3-CH=CH-CH=CH-C2H5 c bn ng phn hnh hc

Th d 2: CH3-CH=CH-CH=CH-CH3 ch c ba ng phn hnh hc

Hp cht c ni i ly tch Cumulen vi s chn ni i c ng phn quang hc. Cumulen vi s l ni i c ng phn hnh hc.

H

C 2H 5

HCH3

H H

H

H

C2H5H

HCH3

cis - 2 - cis - 4 trans - 2 - trans - 4

H 3 C 3

H 3

CH

H C

HH H

H cis - 2 - cis- 4.

H

H

C H

H3

trans - 2 trans - 4 .

C

H

CH3 H

HHH3

trans - 2 cis-4 ( hoac cis - 2 trans-4 )


HCl

H

Cl

Cl

Cl

H

H

CH3

Cl

H

H

H

Cl

H

CH3

C2H5OOC

H

COOC2H5

H

C2H5OOC

COOC2H5

H

H

Th d: Nm 1959, Kuhn c lp c hai ng phn 1,4-di-m-nitrophenyl-1,4-diphenylbuta.trien

3.2.3. Tnh cht vt l ca ng phn hnh hc 3.2.3.1. Momen lng cc Hp cht kiu abC = Cab nu lin kt C-a c momen

lng cc ln, lin kt C-b khng c momen lng cc th ng phn cis phi c momen lng cc rt ln, mt khc ng phn trans c trung tm i xng nn momen lng cc tng bng khng.

Th d: 1,2 dicloroeten

cis = 1,89 D trans = 0

Nu nhm a- y electron, cn nhm b- rt electron th momen lng cc ca phn t bng tng s momen lng cc ca chng. Do ng phn trans c gi tr momen lng cc ln hn ca ng phn cis.

trans = 1,97 D cis = 1,71 D

Khi tnh Momen lng cc ca nhng anken mang nhm th phc tp s gp nhiu kh khn.

cis = 2,54 D trans = 2,38 D

3.2.3.2. Tnh cht vt l

N O 2

C C

NO 2

NO 2

C C

O 2NCis Trans


CH CHCH COOHCH

Nhit nng chy: Nhit nng chy ca ng phn trans thng ln hn ca ng phn cis (tr mt s trng hp ngoi l), do ng phn trans c tnh i xng cao hn ng phn cis nn mng tinh th sp xp cht hn.

Nhit si, t khi, chit sut l nhng hm nghch ca th tch phn t cho nn ng phn no m mt trong ba c tnh va ri c tr s ln th thng thng hai c tnh kia cng c tr s ln.

Tosi (oC) d20 (g/ml) n20 Hp cht Cis Trans Cis Trans Cis Trans

CHCl = CHCl

CH3 CH = CH - Cl

CH3 CH = CH - CN

C2H5OOC-CH=CH-COO C2H5

0,03

32,8

108

223

48,4

37,4

122

218

1,2835

0,9350

0,8244

1,0520

1,2565

0,9350

0,8239

1,0670

1,4486

1,4055

1,4182

1,4411

1,4454

1,4054

1,4216

4,4415

Tnh cht vt l ca mt s ng phn hnh hc

ha tan, thiu nhit, nhit hidrogen ha v hng s ion ha ca cc ng phn trans thng thp hn ca ng phn cis.

Tonng chy (oC) pKa Thiu nhit Hp cht

Cis Trans Cis Trans Cis Trans HOOC CH = CH - COOH

CH3 CH = CH - COOH

130

15,5

lng

68

287

72

125

133

1,9

4,44

_

3,96

3

4,70

_

4,44

327

486

1769

1047

320

478

1739

1040

Cc hng s vt l ca mt s ng phn hnh hc

3.2..3.3. phn ly ca acid phn ly ca acid etylendicarboxilic ph thuc nhiu vo

cu hnh. Acid maleic (cis) K1 = 1,3.10-2 K2 = 3,2.10-7 Acid fumaric (trans) K1= 10-3 K2 = 3,2.10-5 Acid cis - crotonic pKa = 4,44 Acid trans - crotonic pKa = 4,70

3.2.3.4. Cc loi ph Ph t ngoi (UV) (Ultraviolet Spectrum)


Tia X Vin UV UV Kh kin Cn IR IR Vi sng 0,1nm 100nm 200

nm 400nm 0,4

800nm 0,8

8 25

Cc ng phn cis - trans ca nhng anken n gin (but-2-en) hp th nhng di sng khc nhau di 200 nm trong vng t ngoi, nhng khc nhau ny kh phc tp v nm trong vng m thc nghim khng d g o c.

Nhng nhng khc nhau gia cc ng phn cis, trans trong cc olefin kiu abC = Cbd th d dng quan st v y cc nhm th a, d c th tham gia lin hp vi h olefin (a, d c th ging nhau).

Trong nhiu trng hp, cc ng phn cis c cc i hp th di sng ngn hn (() ng thi h s hp th (() ng phn cis trong mi trng hp u nh hn nhiu so vi ng phn trans. iu c th gii thch rng trong ng phn cis do nh hng khng gian nn s lin hp trong phn t b vi phm, cn cc ng phn trans s lin hp vn bnh thng.

TRANS CIS Hp cht Cng thc max max Stilben -metylstilben 1-phenylbutadien Acid cinamic

Ph-CH=CH-Ph Ph-C(CH3)=CH-Ph Ph-CH=CH-CH=CH2 Ph-CH=CH-COOH

295,5 270 280 295

29000 20000 28300 27000

280 260 265 280

10500 11900 14000 13500

Ph t ngoi ca mt s ng phn t ngoi

Ph hng ngoi (IR) Infrared Spectrum Cc ng phn hnh hc c ph hng ngoi khc nhau vng

1650 cm-1 (dao ng ha tr C=C) v cc vng 970,69cm-1 (dao ng bin dng phng =C-H).

Mun cho dao ng phn t c th gy nn s hp th trong vng hng ngoi th momen lng cc ca phn t phi thay i. Hin nhin l s thay i nh vy khng xy ra khi c dao ng ha tr C=C. Trong trans-1,2-dicloroetylen, v momen lng cc ca phn t bng khng v vn gi nguyn gi tr trong sut thi gian dao ng. Kt qu l trong ph hng ngoi ta khng thy nhng tn s dao ng ha tr thuc v ni i ca trans-1,2-dicloroeten, mt khc cis-1,2-dicloroeten li hp th mnh 1590 cm-1 trong ph hng ngoi.


HHPh

COOH H H

Ph COOH

Nh ph hng ngoi c th phn bit c S-cis v S-trans ca cc (, ( khng no. So vi hp cht S-trans th hp cht S-cis c di mnh hn, ng vi dao ng ha tr ca lin kt C=C (khong 1.625 cm-1), ca lin kt C=O (khong 1700 cm-1). Nh vy t s cng ca cc di C=O v C=C i vi cc ng phn S-cis vo khong 0,7 _ 2,5, cn i vi ng phn S-trans vo khong 6 _ 9. Ph cng hng t ht nhn (NMR)

(Nuclear Magnetic Resonance Spectrum) Ph NMR cng c th c dng xc nh cu hnh ca

cc ng phn hnh hc anken dng aCH=CHb. Proton trans-vinyl ghp vi nhau mnh hn proton cis-vinyl.

Do , hng s ghp JHH ca ng phn trans (11-18 Cps) cao hn hng s ghp ca dng cis (6-14 Cps) tng ng.

JH-H= 15,8 Cps JH-H= 12,3 Cps

Acid cinamic

3.2.4. bn tng i v s chuyn ha tng h gia cc ng phn hnh hc

bn c th l v mt nhit ha hc v c o bi nhit hnh thnh, hoc l v mt nhit ng hc c o bi nng lng hnh thnh. Do s khc nhau v bn gia cc ng phn cis v trans c th c biu din s khc nhau v Entalpi hay nng lng t do.

C th o mc khc nhau v bn nhit ha hc ca cc ng phn hnh hc bng cc i lng ca thiu nhit. Nhng chnh xc ca phng php ny cng b hn ch, bi v cc thiu nhit rt ln nhng s khc nhau ca chng th li nh.

V tnh bn nhit ng tng i ca cc ng phn hnh hc c th d on theo nng lng t do hnh thnh nu bit c nng lng ny.

Th d: nng lng t do hnh thnh ca trans-but-2-en 25oC ln hn nng lng t do hnh thnh ca ng phn cis l 2,884 KJ/mol. Cn ch rng i lng ny nh hn hiu s tng ng ca entalpi (3,971 KJ/mol) bi v cis-but-2-en c entalpi ln hn trans-but-2-en l 4,347 kJ/mol.


RH

R

H+ Br

R

H

Br

R H

H

R

Br

R H

R

H

H

R+ Br

NOH

CH

CH3N

OH

C

H

CH3..

..NC

Nng lng t do hnh thnh i vi nhiu i ng phn hnh hc vn cn cha bit ht. Tuy vy, c hai ng phn trong cn bng ha hc v t trng thi cn bng c tnh trc tip hiu s nng lng t do.

Th d: trong hn hp cn bng ca cis-, trans-but-2-en 3900C cha 52,8% ng phn trans.

Phng php n gin nht c s chuyn ha tng h ca cc ng phn hnh hc l un nng chng.

Th d: i vi Stilben hng ro nng lng ca s chuyn ha tng h bng 167,2(188,1KJ

thc hin qu trnh ng phn ha cis-trans c th dng cc xc tc khc nhau nh: gc t do, ngun sinh ra gc t do nh NxOy, cc halogen (c mt nh sng), cc axit: HX (X: halogen), H2SO4, BF3, kim loi kim (natri), tc nhn hidro ha,dehidro ha nh Pt, Se.

Th d: s ng ha cis-trans vi xc tc gc t do:

Mun c Br( ta dng Br2 vi nh sng c di sng tng i ln (cc i hp th i vi Brom l 415A0)

3.3. HP CHT C NI I C=N HAY N=N 3.3.1. ng phn hnh hc ca Oxim Aldoxim, cetoxim c ng phn hnh hc c gi l syn-

hay anti-

Syn Acetaldoxim Anti Acetaldoxim (So snh v tr tng i gia nhm OH v H)


NOH

CCH3

..

NC

N

CH3

CO

CH3

NNH

C N

NH-C-NH2

C

HOOC

NO2

CO

O

.. ..

Cetoxim: c ng phn hnh hc khi nguyn t carbon (sn phm) lin kt vi hai nhm khc nhau.

Syn metylphenylcetoxim hay Anti metylphenylcetoxim

xc nh cu hnh syn- hay anti- ta so snh v tr tng i ca nhm OH vi nhm th c c trc.

Hp cht khc c ni i Nitron: s ankyl ha oxim thng cho mt hn hp

dn xut O-ankyl v N-ankyl. ng phn hnh hc ca N-ankyl gi l NITRON c chng minh bi hp cht sau

phenyl p totyl N metylnitron

bng s kho st momen lng cc. Phenyl hidrazon v semicarbazon

Phenyl hidrazon ca acid O-nitrophenyl glioxilic v monosemicarbazon ca benzyl cng c ng phn hnh hc.

Phenylhidrazon Monosemicarbazon ca benzyl

ca Acid O nitrophenylglioxilic


NNAr

ONN

Ar O

....

....

NCN

NAr

NCN

NAr

.. .. ....

N NN N.. ..

....

3.3.3. ng phn hnh hc ca hp cht c ni i N=N Diazoat

anti arildiazoat syn arildiazoat

syn-diazoat khng bn, anti-diazoat bn. ng phn syn- hp th di sng ngn hn v cng hp th thp hn ng phn anti.

Diazocianur

syn anti

ng phn syn khng bn v chuyn ha thnh ng phn anti d dng khi yn hay un nh, ngc li ng phn anti chuyn thnh syn di nh hng ca s chiu x.

Azobenzen

= 0 = 3D trans azobenzen cis azobenzen

Thng thng ng phn trans bn hn ng phn cis, di s chiu x bng nh sng t ngoi, ng phn trans bin i mt phn thnh ng phn cis, c th c lp c bng phng php kt tinh hay ngoi hp trn Al2O3.

C cu ca hai dng ny c xc nh bng nhiu x tia X. Trans azobenzen l mt phn t c c cu gn phng, cn ng phn cis azobenzen c c cu ghnh, trong hai nhn benzen nm ngoi mt phng cha hai nguyn t Nit, to thnh gia hai nguyn t Carbon i din mt khong trng chng 3,34A0.


NNO

N NO

.. ..

H

CH3

H

CH3

H

CH3

CH3

H

H

C2H5

H

CH3

H

CH3

H

C2H5

H

H

CH3

H

C2H5

H

H

CH3H3CH3C

Azoxibenzen: cng c hai ng phn hnh hc:

cis azoxibenzen trans azoxibenzen

Khi un trn nhit nng chy, ng phn cis chuyn thnh ng phn trans.

3.4. HP CHT VNG NO Cc cicloankan mang nhng nhm th thch hp cng c ng

phn hnh hc. Cis 1,2 dimetylciclopropan Trans 1,2 dimetylciclopropan

Cc vng c nhiu s nguyn t Carbon v mang nhiu nhm th cng c tng s ng phn hnh hc nhiu hn (c c ng phn quang hc)

Cis cis Cis trans Trans trans ( Trans cis )


Chng 4: NG PHN CU TRNG CA HP CHT KHNG VNG

1. 1.1. Khi nim v cu trng (conformation) 1.2. Php phn gii cu trng 1.3. Cu trng ca hidrocarbon no

1.3.1. Etan 1.3.2. nbutan 1.3.3. npentan 1.3.4. nhexan

1.4. Cu trng ca hidrocarbon no mang nhm th 1.4.1. Halogenur etyl 1.4.2. 1,2dicloroetan 1.4.3. Etanol mang nhm th v tr s 2 1.4.4. 2,3dibromobutan

1.5. Cu trng ca hp cht khng no 1.5.1. Hp cht c ni i C=O, C=C, N=C 1.5.2. Hp cht c ni i lin hp 1.5.3. S quay quanh ni i


4.1. KHI NIM V CU TRNG Khi nim v cu trng dng ch cc dng hnh hc ca

phn t c to thnh do s quay quanh lin kt n m khng b gy lin kt (nn cn gi l ng phn quay Rotamer)

V mt l thuyt, mt phn t c v s cu trng vi mc nng lng khc nhau, ty theo bn cht ca cc nguyn t lin kt cng ha tr v nh hng gia cc nguyn t khng lin kt trong phn t, cu trng c coi l n nh nht ng vi mc nng lng thp nht, khi tng tc gia cc nhm nguyn t trong phn t t nht. Tuy nhin, v hiu s nng lng v thi gian cc nguyn t ti nhng v tr khc nhau rt nh nn cc cu trng khng th c lp c (tr vi trng hp c bit).

Th d: Acid mesotartric c hai cu trng (cng mt cu hnh = Configuration)

Hai cu trng ca acid Mesotartric

4.2. PHP PHN GII CU TRNG

Trong a s trng hp, s quay quanh cc ni n khng hon ton t do v vi cu trng bn hn cu trng khc. Php phn gii cu trng gii thch phn ng v tnh cht ca hp cht da trn cu trng ca n: trng thi cn bn, trng thi kch thch v trng thi chuyn tip.

Cu trng ca mt phn t c th xc nh bi: _ Phng php vt l: nhiu x in t, nhiu x tia X,

ph t ngoi, hng ngoi, cng hng t ht nhn, momen lng cc, tn sc quang hot

_ Phng php ha hc: ng hc c th dng c nh kho st v vn

tc phn ng este ha, dung mi gii carboxilat, cc tosilat

mat phang oi xng

H

O H

C OO HHH O O C

H O

H

C O O H

O H H H O O C

H O

tam oi xng


cau trang lech cau trang che khuat

H H

H

H

HH

C 2C1

Nhit ng lc hc cng c th cho bit cu trng u i, suy ra t trng thi cn bng gia cc hp cht ng phn lp th.

S phn gii cu trng c p dng trc ht cho cc h vng ciclohexan sc hp: Stroid, triterpenoid v c cu cng rn ca cc hp cht ny thng ch a n mt cu trng duy nht nn kt qu rt kh quan.

4.3. CU TRNG CA HIDROCARBON NO 4.3.1. Etan Theo ha hc c in, hai nhm metyl ca etan c th quay

quanh ni n CarbonCarbon mt cch t do, nhng vi phng php phn gii cn i ngi ta chng minh rng ch c s dao ng quanh mt vi v tr c u, hai cu trng cc oan ca etan l cu trng lch v cu trng che khut c biu din bi cng thc chiu sau y:

_ Cng thc phi cnh

_ Cng thc Newman:

Nhn theo trc CarbonCarbon, thy cc ni CH ca mt nguyn t carbon trong cu trng lch l nhng ng phn gic ca cc gc HCH ca nguyn t carbon kia. Etan c ba cu trng lch ging nhau, to thnh khi nhm metyl ca cu trng lch quay 1200 quanh ni n CarbonCarbon.

Gc quay c xc nh chnh xc hn bi gc xon (gc nh din), l gc gia hai mt phng:

__ Gc xon __

H

H

H

H

HH


mt mt phng xc nh bi mt ni CH ch nh ti nguyn t Carbon s 1 vi ni C1C2 v mt phng th hai xc nh bi mt ni CH ch nh ti nguyn t Carbon s 2 vi ni C2C1

Trong cu trng lch, gc xon ( = 600 cn trong cu trng che khut gc xon ( = 00

Gc xon bin thin t 00 n 3600 khi nhm metyl quay quanh lin kt CC.

S bin thin nng lng theo gc xon l mt ng cong gn hnh sin vi ba cc i v ba cc tiu, cao ca ro nng lng trong etan l 2,8 Kcal/mol.

Cu trng lch bn nht, v c mc nng lng ti thiu, cu trng che khut ng vi mc nng lng cao nht nn khng bn. Nh vy, bnh thng Etan c cu trng lch cn cu trng che khut l mt trng thi chuyn tip to ra khi phn t Etan quay t cu trng lch ny n cu trng lch khc.

V ro nng lng ca s quay kh thp, cc phn t c dy h c coi nh quay t do quanh ni n, nhit thng.

Biu nng lng quay ca Etan

4.3.2. nbutan CH3CH2CH2CH3 S bin thin nng lng trong nbutan vi gc xon l

ng cong hnh sin (tng t vi etan) ng vi cc cu trng:


Che khut ton phn (( = 0): do sc y gia hai nhm metyl che khut lm cho mc nng lng tng thm 3 Kcal/mol.

Che khut mt phn (( = 1200, ( = 2400): sc y Van Der Waals gia hai nhm metyl gim xung khong 0,8 Kcal/mol. ng vi trng thi ny c tng tc gia nhm Metyl v Hidro che khut vi mc nng lng khong 1 Kcal/mol. Tuy nhin, cu trng che khut mt phn v cu trng che khut ton phn khng phi l ng phn cu trng v ch c xem l nhng trng thi chuyn tip gia ng phn bn lch v i lch.

_ Cu trng bn lch: ng vi mc nng lng khong 0,8 Kcal/mol vi gc xon ( = 600 hay ( = 3000, cn gi l cu trng ghnh hay syn.

_ Cu trng i lch: n nh nht vi mc nng lng thp nht, vi gc xon ( = 1800. Cu trng i lch cn gi l cu trng trans hay anti.

nhit thng, nbutan l mt hn hp ng phn cu trng i lch v bn lch, trong cu trng i lch chim thnh phn nhiu hn.

Nng lng quay trong nbutan

tng tc Metyl H tng tc Metyl Metyl ro nng lng trong Etan (tng tc H H)


CH3

HH

HH

C

H H

CH3 H H

H HCH3

C

H H

CH3

CH3

HH

HH

C

CH3 H

HH H

H HCH3

C

CH3 H

H

H

H H

HH

H H

H H

H H

C

H

HH

Nng lng ton phn

4.3.3. npentan Vi hai trc quay trong C2C3 v C3C4 th phn t n

pentan c th c tt c by cu trng (i lch v bn lch). Ph Raman cho bit c hai cu trng tn ti trong npentan th lng, cu trng u i c nhm CH3 v C2H5 i lch, k l cu trng bn lch. Hiu s nng lng gia hai cu trng c chng 0,5 0,7 Kcal/mol. Cc cu trng khc cha nhiu dng bn lch hn do t bn hn.

Cu trng i lch ca npentan

Cu trng bn lch ca npentan 4.3.4. nhexan Phn t nhexan c ba trc quay trong v c th c 12 cu

trng, cu trng i lch chim ( nhiu nht trong cn bng, tng t npentan, phn t nhexan cng c hiu s nng lng gia cu trng i lch v bn lch c chng 0,5 Kcal/mol.

Cu trng i lch trong nhexan Theo ph Raman, nankan c 12 nguyn t Carbon c cu

trng hon ton i lch trng thi kt tinh. Tuy nhin, trng thi lng c mt s cu trng bn lch ng k ti bt c ni no


Cl

H H

H H

Cl

Cl

H H

H Cl

H

v bt c lc no. Hiu s nng lng gia cu trng i lch v bn lch c chng 0,8 Kcal/mol.

4.4. CU TRNG CA HIDROCARBON NO MANG NHM TH

4.4.1. Halogenur etyl S thay th mt nguyn t Hidro trong etan bng mt nguyn

t Halogen khng lm thay i ro nng lng mt cch ng k. Dng phng php ph nghim, ngi ta tm thy tr s ro nng lng nh sau:

CH3CH2F CH3CH2Cl CH3CH2Br 3,33 3,50 3,50 (Kcal/mol)

4.4.2. 1,2dicloroetan Vi cc phn t phc tp, ngi ta cn xt n nhng tng

tc khc hn tng tc lp th nh: tng tc lng cc, lc ni hidrogen ni phn t

Phn t 1,2dicloroetan c cu trng bn lch km bn hn cu trng i lch, do lc x y lng cc mnh hn, mc d tng tc lp th km bn hn trong nbutan.

i lch Bn lch

Cu trng ca 1,2dicloroetan

Nhiu x tia X chng minh 1,2dicloroetan kt tinh hon ton di cu trng i lch.

Ph hng ngoi v Raman cho thy 1,2dicloroetan trng thi rn c mt tm i xng, nh vy tn ti di cu trng i lch, khi ha lng mt s phn t bin i


Cl

H H

H H

OH

Cl

H H

H O

H

H

...

thnh cu trng bn lch (c chng minh bng s gia tng s vch trong ph hng ngoi v Raman)

Nhiu x in t cho thy 1,2dicloroetan trng thi kh cha 73( cu trng i lch v 27( cu trng bn lch ( 220C), hiu s nng lng gia hai cu trng ny khong 1,03 1,32 Kcal/mol.

Momen lng cc ca cu trng u i c tr s bng 0 (cu trng i lch). Thc nghim cho bit momen lng cc tht s ca 1,2dicloroetan thay i theo nhit t 1,12 D 320C n 1,54 D 2700C, s kin ny ph hp vi mt cn bng gia cc cu trng i lch v bn lch.

4.4.3. Etanol mang nhm th v tr s 2 RCH2CH2OH

R: OH, NH2, F, Cl, Br, OCH3, NO2, NHCH3 Thng thng cu trng i lch bn hn cu trng bn lch.

Tuy nhin, t l n nh c th o ngc vi mt s hp cht c c cu c bit.

Th d: cu trng bn lch ca etylen clorhidrin bn hn cu trng i lch bt c iu kin no, th rn ch c cu trng bn lch tn ti; th lng hoc kh, mt cn bng c thit lp gia cu trng bn lch v i lch, nng lng ca cu trng bn lch thp hn nng lng ca cu trng i lch 0,95 Kcal/mol do cu trng bn lch c lin kt Hidro ni phn t.

i lch Bn lch

Cu trng ca Etylenclohidrin

Tng qut, tt c cc RCH2CH2OH vi R l OH, NH2, F, Cl, Br, OCH3, NO2, NHCH3 u c cu trng bn lch n nh hn cu trng i lch nh lin kt hidro ni


CH3

Br

H

H CH3

Br

BrHBr

H3C H

CH3

BrBrCH3

H3CH

H

CH3

Br

H

H3C H

Br

BrCH3Br

H3C H

H

BrBrH

H3CH

CH3

C CH2 N CH2 C O

phn t gia nhm R vi OH, mc d c s x y lp th v lng cc gia hai nhm ny.

4.4.4. 2,3dibromobutan 2,3dibromobutan c hai ng phn: Eritro (cng l Meso) v

Treo. Nhiu x in t cho bit ng phn Meso tn ti di cu

trng i lch A; cn ng phn Treo tn ti di cu trng B c hai nguyn t Brom i lch nhau, hai nhm CH3 bn lch

meso (A) (A1) (A2)

treo (B) (B1) (B2) _ ng phn meso cho kt qu bt ng l cc cu trng bn

lch ng gp n 30% trng thi lng tinh khit, nhng trong CS2 t l trn bnh thng gim xung 20%.

_ ng phn treo cha khong 20% cu trng B2, v phn cn li l cu trng B v B1.

Trong dung mi khng cc; hai nguyn t Brom bn lch t thun li hn hai nguyn t Brom i lch. Cu trng B c hai nguyn t Brom i lch v hai nhm metyl bn lch, cn cu trng B1 c hai nguyn t Brom bn lch v hai nhm metyl i lch.

4.5. CU TRNG CA HP CHT KHNG NO 4.5.1. Phn t cha nhm , , Trong phn t aldehid acetic CH3CH=O v propen CH3

CH=CH2 u tn ti di cu trng vi ni i C=O hay C=C v


H H

H O

HH H

H CH2

HH H

H3C O

H

H CO

OCH3 H CO

OCH3

H

O

CH3

C

O

H

O

CH3

C

CH2

CH 2

N O

H

CH2

H

CH2

H

CH2

H

H

CH2

nguyn t Hidro che khut nhau c xc nhn bi ph nghim viba v nhiu x in t.

CH3CHO CH3CH=CH2 CH3CH2CHO

Trong phn t propanal, xc nh bi hng s ghp cng hng t ht nhn nhm CH3 che khut ni i C=O. Kt qu ny c th gii thch bi sc ht lng cc gia CCH3 vi C=O.

Vi cc phn t ; CH3OCH=CH2 ; th cu trng u i ng vi ni i C=O, C=C, C=N u che khut nhm CH3. iu ny c chng minh bi ph hng ngoi, ph viba v nhiu x in t.

Metyl formiat Metyl vinyl eter

Cu trng u i ca formaldoxim c ni i C=N v ni OH i nhau.

iu ny c th c gii thch bi s x y gia electron p v ( trong metyl formiat, metyl vinyl eter ; v gia in t p trong formaldoxim.

4.5.2. Phn t c ni i lin hp Phn t c ni i lin hp c th c ng phn cu trng,

l ng phn Scis v Strans (Single: n). Tip u ng S t trc ch cis v trans ch cu trng lin h n ni n trong h lin hp.


OCH3 H

C CH3

H

O

CH3

H

C

H

CH3

S_cis S_trans

Cu trng ca buta-1,3-dien

Kt qu thc nghim da trn tnh cht nhit ng hc, nhiu x in t, ph nghim hng ngoi v viba cho bit cu trng Strans ca buta-1,3-dien bn hn cu trng Scis t nht 2 Kcal/mol.

Ngoi ra, ph hng ngoi v Raman chng minh trans-pent-3-en-2-on l mt hn hp cn bng cha cu trng Scis v Strans vi s lng bng nhau.

S_cis S_trans Cu trng ca Trans-pent-3-en-2-on .

Phn t buta-1,3-dien cho phn ng dielalder d dng, chng t phn t t n cu trng Scis khi cn thit. Tht ra, ro nng lng trong s quay quanh ni n c tr s khong 4,9 Kcal/mol.

4.5.3. S quay quanh ni i Ro nng lng ca s quay quanh ni i CarbonCarbon c

tr s kh cao (40 Kcal/mol vi etylen) so vi s quay quanh ni n (2,8 Kcal/mol).

Tnh bn vng ca ni i CarbonCarbon c gii thch bi s hnh thnh orbitan (. Nu mt phng ca mt nguyn t Carbon ni i quay 900 quanh ni sigma (cc; orbitan phn t b ph hy v trc i xng ca hai orbitan vung gc nhau nn khng xen ph ln nhau.

Hp cht Cng thc Ro nng lng (Kcal/mol)


Etylen 2buten Acid butendioic Stilben

CH2=CH2 CH3CH=CHCH3 HOOC-CH=CH-COOH PhCH=CHPh

40 18

15,8 42,8

ng phn trans-but-2-en bn hn cis-but-2-en khong 1 Kcal/mol.

Cn trans1,2dicloroeten li t bn hn cis tng ng 0,5 Kcal/mol.

V 2,2,5,5tetrametylhex-3-en c cu hnh trans bn hn cu hnh cis khong 9Kcal/mol.


Chng 5: CU TRNG CA HP CHT VNG NO

5. 5.1. Tnh bn ca hp cht vng no

5.1.1. phn ng ca ciclopropan, ciclobutan 5.1.2. Thuyt cng Baeyer 5.1.3. Thiu nhit v tnh bn tng i ca cc

cicloankan 5.1.4. Khi nim vng khng cng ca Sachse v Mohr 5.1.5. Sc cng Pitzer

5.2. Cu trng ca hp cht vng nh 5.2.1. Ciclopropan 5.2.2. Ciclobutan

5.3. Cu trng ca hp cht vng trung bnh 5.3.1. Ciclopentan 5.3.2. Ciclohexan

5.3.2.1. Cu trng gh 5.3.2.2. Cu trng tu 5.3.2.3. Cu trng tu xon

5.3.3. Ciclohexan mang nhm th 5.3.3.1. Ciclohexan mang mt nhm th 5.3.3.2. Ciclohexan mang hai nhm th 5.3.3.3. Ciclohexan mang nhiu nhm th

5.4. Cu trng ca vi hp cht hai vng sc hp 5.4.1. Decalin 5.4.2. Hidrindan 5.4.3. Decalol 5.4.4. Hidrindanol

5.1. TNH BN CA HP CHT VNG NO

Cc hp cht vng no bit trc nm 1880 u l chuyn ha cht ca ciclohexan. Vi nh ha hc nh Meyer (1876) cho rng cc vng khc hn vng c su nguyn t khng th to thnh. Tuy nhin, nm 1881, Markovnikov tng hp mt chuyn ha cht ca ciclobutan v Freund iu ch ciclopropan. Nm 1883,


+ H2 80oCNi CH3-CH2-CH3

+ CH2Br-CH2-CH2BrBr2+ CH3-CH2-CH2BrHBr

+ HI CH3-CH2-CH2-CH2I

Perkin kho st cc hp cht c vng nh v iu ch mt s chuyn ha cht ca ciclopropan, ciclobutan v ciclopentan trng thi tinh khit.

5.1.1. phn ng ca ciclopropan, ciclobutan Thng thng tnh cht ca cc cicloankan ging tnh cht ca

ankan tng ng. Nhng cc vng nh ciclopropan v ciclobutan c ha tnh tng t cc anken. Do , etylen c xem nh hp cht vng nh nht ch gm hai nguyn t Carbon.

Ciclopropan tham gia phn ng vi: _ Hidro

_ Vi Brom, HBr, HI v H2SO4

_ Khc hn vi propen, ciclopropan khng b oxi ha bi dung dch KMnO4.

Ciclobutan t c khuynh hng cho phn ng cng hn ciclopropan, nhng c th hidrogen ha vi xc tc Ni, 1800C cho nbutan.

_ Vi HI:

t0

_ Vi Br2, HBr, KMnO4 cng khng tc dng vi ciclobutan.

5.1.2. Thuyt cng Baeyer Baeyer gi s cicloankan l nhng a gic u v phng v

tnh lch ca gc ni trong cc cicloankan i vi t din bnh thng.

lch ca ( mi gc ni trong vng gi l sc cng gc hay sc cng Baeyer.

2 oC3 2 2 3 + H Ni180 CH -CH -CH -CH


o1 (109,5 )2

= * ( l gc trong ca vng * H s gii thch s

phn phi sc cng ng u gia hai ni lin h

n = s cnh ca vng lch gc ca cicloankan

N n 3 4 5 6 7 8 9 10

600 900 1080 1200 128,6 135 140 144

+24,7 +9,7 +0,7 5,3 9,6 12,8 15,3 17,3

11 12 13 14 15 16 17

147,3 150 152

154,3 156

157,5 159

18,8 20,3 21,5 22,4 23,3 24

24,7

T cc tr s trn cho thy:

lch ca gc ni trong ciclopropan (+24,70) ln hn ca gc ni trong ciclobutan (+9,70) nn ciclopropan cng hn ciclobutan, do ciclopropan t bn hn v cho phn ng m vng d dng hn ciclobutan.

Ciclopetan c lch b nht (+0,70); c th xem nh khng cng ngha l theo Baeyer ciclopentan l hp cht vng bn nht.

Ciclohexan c lch ng k (5,30), gy ra mt sc cng nh trong phn t (im ny khng ng).

T ciclohexan tr i, lch tng dn v u, ciclopropan c lch ging nh cicloankan c 17 nguyn t Carbon.

Tm li, Baeyer cho rng cc vng nh hn hoc ln hn ciclopentan v ciclohexan u khng bn nn cho phn ng m vng d dng vi ciclopropan v ciclobutan; mt khc cc vng


ln hn gp nhiu kh khn trong iu ch (iu ny cng khng ng).

5.1.3. Thiu nhit v tnh bn tng i ca cicloankan Tnh bn tng i ca cc hp cht mt vng c th xc nh

bi thiu nhit. Thiu nhit c tr s thc nghim cao nht vi ciclopropan,

gim dn n cc tiu vi ciclohexan ri gia tng n cc i vi ciclononan, sau cng gim xung cc tiu vi ciclotetradecan.

(2) H/n (Kcal/mol): thiu nhit tnh cho mi nhm CH2 ca hp cht cicloankan ( th kh) (3) (H/n157) Kcal/mol: hiu s thiu nhit tnh cho mi nhm CH2 ca cicloankan v nankan tng ng (4) Tng s sc cng ca ciclan

(1) (2) (3) (4)

n H/n H/n157,4 1/n(H/n157,4) 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

nankan

166,6 164,0 158,7 157,4 158,3 158,6 158,8 158,6 158,4 157,7 157,8 157,4 157,5 157,5 157,2 157,4

9,2 6,6 1,3 0,0* 0,9 1,2 1,4 1,2 1,0 0,3 0,4 0,0* 0,1 0,1

0,2 0

27,6 26,4 6,5 00 6,3 9,6 12,6 12,0 11,0 3,6 5,2 00 1,5 1,6 3,4 00

Thiu nhit ca cicloankan tnh cho mi nhm metylen (Kcal/mol)


Thiu nhit tnh cho mi nhm metylen trong ciclopropan v ciclobutan cao hn thiu nhit tng ng ca nankan bi 9,2 v 7,6 Kcal/mol theo th t, ngha l ciclopropan v ciclobutan cha nhiu nng lng tnh cho mi nhm metylen hn do chng km bn hn propan v butan. iu ny ph hp vi thuyt Baeyer.

Thiu nhit ca ciclohexan b nht, bng ca nhexan nn ciclohexan l hp cht bn nht ch khng phi l ciclopentan nh Baeyer nu.

Thiu nhit ca cc vng c t 7 n 11 nguyn t Carbon u ging thiu nhit ca npentan v thiu nhit ca cc vng c t 12 nguyn t Carbon tr ln khng th phn bit vi thiu nhit ca nankan. Nh vy, tri vi thuyt Baeyer, tnh bn ca cc vng ny khng km hn cc hp cht mch h mt cch ng k. Hn na, cc vng ln t ciclotetradecan tr ln u hon ton khng cng v khng c khuynh hng cho phn ng m vng nh ciclopropan v ciclobutan.

Da vo thiu nhit, Eliel (1962) chia hp cht vng thnh bn nhm:

_ Vng nh vi n = 3 v 4. _ Vng bnh thng vi n = 5; 6; 7. _ Vng trung bnh vi n = 8 ( 9; 10; 11 _ Vng ln vi n ( 12.

5.1.4. Khi nim vng khng cng ca Sachse v Mohr Nm 1890, Sachse cho rng ciclohexan v cc vng ln hn

c th ghnh p ng iu kin gc t din v tn ti di nhng cu trng khng phng v khng cng, quan im ny khng c chp nhn lc u v n d on ciclohexan phi tn ti di hai dng: gh v tu trong khi ch c mt dng c bit lc by gi.

dng gh dng tu Cu trng ca ciclohexan


HHH

HHH

Nm 1918, Mohr gii thch rng hai dng gh v tu bin i ln nhau rt nhanh nn khng th c lp c.

5.1.5. Sc cng Pitzer Nng lng ca cc hp cht vng gia tng vi sc cng

Baeyer do s bin dng ca gc ha tr. Nng lng cng c th gia tng bi s to thnh mt cu

trng c dung tch nng lng bt li. S gia tng nng lng khi mt cu trng lch thun li bin i thnh mt cu trng che khut bt thun li, gi l sc cng Pitzer trong phn t.

Sc cng Pitzer do s x y gia cc nguyn t k cn khng ni cn gi l sc cng i ni hay sc cng xon.

Sc cng Pitzer tr nn ng k i vi cc vng nh trong cc nhm tr hon bt buc phi che khut nhau. Th d sc cng Pitzer lm cho ciclopentan khng th c c cu phng ng thi bin dng gc t din, ngha l a n sc cng Baeyer. Mc d s kin ny gia tng nng lng, dng khng phng ca ciclopentan c th nng thp hn th nng ca dng phng, v cu trng tng ng thun li hn v mt nng lng.

5.2. CU TRNG CA CC VNG NH 5.2.1. Ciclopropan

Ciclopropan Vi ba nguyn t Carbon trong vng, ciclopropan c c cu

phng, gc trong ca ciclopropan bng 600 nn phn t ht sc cng, do ciclopropan rt d m vng. Ngoi ra cc ni CH cng mt bn mt phng che khut nhau, lm cho phn t cng khng bn.

S xen ph ca cc orbitan trong ciclopropan


HH H

HHH

HH

HH

H HH

H(e)

(a)

C th trong ciclopropan c s khc nhau no so vi s phn b bnh thng ca cc gc ha tr, y bn lin kt ca nguyn t Carbon khng c c tnh ging nhau l sp3 na; m lin kt CC gn ging vi p(() hn; cn lin kt CH gn ging c tnh s((). Nh vy, lin kt CH c cng c thm, cn gc ha tr HCH v CCH ln hn, cc lin kt CC b lng ra (do gc t din b nh li). Do c s thay i cc gc ha tr nn cc gc ny phn no b lch khi v tr thng thng v mt phng ca vng khng cn l mt phng i xng na.

Theo thuyt c hc lng t; trong iu kin cc gc lin kt 600 th khng th no c s lai ha c, bi v trc ca hai orbitan lai ha sp3 xut pht t mt nguyn t Carbon bao gi cng lp vi nhau mt gc t nht l bng 900. Tuy nhin, nu trc ca cc orbitan lai ha sp3 c hng nh trong hnh v th cc orbitan lai ha khng th tc dng thng trc tip vi nhau c, do chng hi b un cong lm cho s xen ph km i dn n l lin kt CC trong phn t c mt sc cng.

5.2.2. Ciclobutan Bng nhiu x in t hay cc php o ph nghim v nhit

ng lc hc chng minh rng: ciclobutan c c cu ghnh. V nu c c cu phng, cc ni CH cng mt bn mt phng (k cn) s che khut nhau v tng tc khng ni gia cc Hidrogen lm cho ciclobutan phi ghnh i, l cu trng xp.

Cu trng xp ca ciclobutan

Nhiu x in t cho bit nguyn t Carbon ngoi mt phng ca ba nguyn t Carbon cn li to vi mt phng ny mt gc khong 200.

Cc ni trong cu trng xp ca ciclobutan chim v tr trc a (axial) v xch o e (equatorial) (tng t nh trong ciclohexan).

Vng bn cnh t cng hn vng ba cnh nn c th chp nhn bn nguyn t carbon ca ciclobutan trng thi lai ha (sp3).

Vi hai nhm th gn ti v tr 1,3 nh:


eee

a

a

bb

a

e

e

e'

e'

a

a

a'a'b

b ee'

ee'

a

a'

a

a'b

b'1

2

3

4 5 1

2

3

4

5

Cis ee Cis aa

Trans ea Trans ae

3metyl ciclobutan carboxilat metyl

ng phn cis ee bn hn trans ea, iu ny c xc nhn bi thc nghim.

Nhng ng phn transciclobutan-1,3-dicarboxilat dimetyl bn hn ng phn cis tng ng do sc y tnh in gia cc trng cc mnh hn hiu ng lp th.

5.3. CU TRNG CA HP CHT VNG TRUNG BNH 5.3.1. Ciclopentan Ciclopentan phng s c nm nhm metylen hon ton che

khut a n sc cng Pitzer khong 14 Kcal/mol. gim sc cng Pitzer vng ciclopentan phi c cu trng

(hi ghnh) phong b: mt nguyn t Carbon nm ngoi mt phng ca bn nguyn t Carbon cn li.

Cu trng phong b ca ciclopentan Cu trng na gh: ba nguyn t Carbon ca

vng nm trong mt mt phng, cn hai nguyn t kia trn v di mt phng .

H H C H 3 COOCH3

CH3H H

C O O C H 3

C H 3 H H COOCH3

H

CH3

H C O O C H 3


CH3

H3C

CH3

H3C

R1

23

4 5

Cu trng na gh ca ciclopentan

Trong cu trng phong b hay na gh u c ba kiu ni: Ni trc (a) v ni xch o (e) ging nh trong

ciclohexan. Ni ta trc (a) v ta xch o (e). Ni song thit din (b) (biseetional) chim mt v tr gia

ni trc v ni xch o to thnh gc 54,70 vi mt phng ca phn t.

Cu trng na gh cng linh ng nh cu trng phong b, nng lng ca hai cu trng ny khng khc nhau nhiu lm.

Ciclopentan mang mt nhm th Nguyn t Carbon mang nhm th lch ra khi mt phng ca

bn nguyn t Carbon cn li. trnh s tng tc gia nhm th R vi hai nhm metylen v tr 2 v 5 th nhm R v tr xch o (e) thun li hn v tr a (trc).

Th d: metyl ciclohexan c cu trng phong b c an nh hn cu trng xp khong 0,9 Kcal/mol

Ciclopentan mang hai nhm th: Th d: 1,3dimetylciclopentan c cu trng cis (ee) bn hn

cu trng trans (ea) khong 0,59 Kcal/mol. Cis (ee) Trans (ea)

Cu trng 1,3dimetyl ciclopentan

Ph hng ngoi ca ciclopentanol c hai chn ng ha tr: C(OH) trong vng 1065 v 996 cm1 ch nh cho nhm OH ta xch o v song thit din theo th t. Nh vy ciclopentanol tn ti di hai cu trng phong b v na gh.


ea

.

1

2

5

34

64 5

3

6

12

(a)

(a)(e)

(e)

5.3.2. Ciclohexan 5.3.2.1. Cu trng gh: ca ciclohexan khng c sc cng

Baeyer v Pitzer, v cc cp nguyn t Hidro gn trn hai nguyn t Carbon k cn u hon ton lch, nh vy th nng ca hp cht mc ti thiu.

Nm 1943, Hassel nhn thy ln u tin rng cc ni CH trong cu trng gh c hai nhm:

6 ni CH song song vi trc i xng bc 3 ca phn t, gi l ni trc (a).

6 ni sp xp quanh vng gn st mt phng trung bnh ca vng, gi l ni xch o (e).

Trong cu trng gh, mi nguyn t Carbon c mt ni trc v mt ni xch o. Cc ni trc v ni xch o lun phin trn v di mt phng trung bnh.

Cc nguyn t hay nhm nguyn t gn trn nguyn t Carbon c cu hnh ( khi chng hng xung; cu hnh ( khi chng hng ln so vi mt phng trung bnh.

() () () () Trc i xng bc 3 Ni trc (a) Ni xch o (e)

( hnh chiu Newman)

Cu trng gh ca ciclohexan

Khong cch gia hai nguyn t Hidro trong cu trng gh.

Kiu V tr Khong cch A0

Bn lch

1He - 2He 1Ha - 2He

2,49 2,49


HH1

23

4 5 6

fpbs

ebab

fpbs bs

fp

12

345

6

1

23

45 6

ebeb eb

eb

abab abab

bs

bsfp

1

23

4

5 6

Trans Nh trc

1 Ha - 2Ha 1Ha - 3Ha

3,00 2,50

5.3.2.2. Cu trng tu: ca ciclohexan khng c sc cng Baeyer nhng c sc cng Pitzer v bn cp nguyn t Hidro gn hai bn hng tu (2,3 v 5,6) che khut nhau. Mt khc, s tng tc gia nhng nguyn t hidrogen ( gn ti hai Carbon mi tu v li tu (1 v 4) ch gn nhau khong 1,84A0, trong khi bn knh Van Der Waals l 2,4A0. Cu trng tu km bn hn cu trng gh v hiu s nng lng tnh cho hai cu trng l 6,9 Kcal/mol. 1.84A0

2.49A0

2.27A0

nhn bn nhn dc

Khong cch gia cc nguyn t Hidro gn trn hai nguyn t C gn nhau trong cu trng tu ca ciclohexan

Kiu V tr Khong cch A0 Ct c Che khut Bn lch Trans Nh trc

1fp 2eb 2ab 1bs 1bs 1fp 2ab 1fp

4fp3eb3ab2eb2ab2eb3eb2ab

1,84 2,27 2,27 2,49 2,49 2,49 3,00 3,00


123

45

6

1

2

3

4

5

6

H H

HH

H

H

H

H

Cu trng tu Hnh chiu Newman ca cu trng tu

5.3.2.3. Cu trng tu xon Cu trng gh l mt cu trng cng rn, khng th vn mo

c. Cu trng tu, cn gi l cu trng mm do, l mt cu trng linh ng, c th un c d dng thnh nhiu cu trng khc nhau.

Cu trng tu quen thuc khng phi l ng phn cu trng, n ch l trng thi chuyn tip gia hai cu trng. Cu trng tu xon l mt ng phn cu trng, km bn hn cu trng gh.

Cu trng tu xon ca ciclohexan

Trong cu trng tu xon hai nguyn t Hidro ct c (ti C1

v C4) x dch ra xa hn; cn hai nguyn t Hidro trc tu ti C3 v C6 s di chuyn li gn nhau hn. Do , s tng tc ct c gim n mc ti thiu ng thi sc cng Pitzer ti cc ni C2C3 v C5C6 cng gim i mt phn.

Mt khc bn nguyn t H trc tu tr nn lch mt cch quan trng, mc d cha hon ton lch hn.


S bin thin nng lng ca ciclohexan vi cu trng


XH

HH

XH

H

V cu trng gh bn nht, nng lng ca n mc ti thiu (im a). Khi vn chn gh ln hay b lng gh xung, cu trng gh bin thnh cu trng tu xon I (im c) t bn hn cu trng gh khong 5,6 Kcal/mol, nhng phi vt qua mt ro nng lng khong 11 Kcal/mol, ng vi cu trng na gh I (im b).

Cu trng tu xon I c th bin i thnh cu trng tu xon II (im e) ngang qua trung gian tu (im d) t bn hn cu trng tu xon khong 1,6 Kcal/mol. Cui cng cu trng tu xon II (im e) bin thnh cu trng gh II (im g) i hnh vi cu trng gh I v trung gian trong giai on ny l cu trng na gh II (im f).

Kt lun: _ Phn t ciclohexan c hai cu trng gh i hnh bin i

ln nhau rt nhanh nhit thng. _ Cc nguyn t Hidro (trc) trong cu trng th I tr thnh

xch o trong cu trng th II v ngc li. _ Hiu s nng lng gia cu trng gh v cu trng tu

xon ca phn t ciclohexan a n mt hn hp cha khong 10.000 cu trng gh v mt cu trng tu xon ( 250C).

5.3.3. Ciclohexan mang nhm th 5.3.3.1. Ciclohexan mang mt nhm th

2,55A0 2,55A0

2,8A0

a) Ankylciclohexan

_ Metylciclohexan Khi nhm CH3 v tr xch o, khong cch

gia cc nguyn t Hidro ca CH3 v cc nguyn t Hidro gn nht ca vng l 2,5A0, ngha l ln hn tng s bn knh Van Der Waals ca hai nguyn t H (2,4A0).

Khi nhm CH3 v tr trc, mt nguyn t H ca nhm ny (hng v vng) gn cc nguyn t H trc ca vng c chng 1,8A0 nn nhm CH3 (a) phi chu sc y Van Der


HHCH3CH3CH3

CH3

CH3

CH3

OH

OH

Waals; sc y ny tng ng vi s tng tc nbutan bn lch. Do , mun bit metylciclohexan c cu trng no bn nht, ngi ta so snh tng s n v butan i lch v butan bn lch trong hai cu trng.

Metylciclohexan trc c hai tng tc butan bn lch, cn metylciclohexan xch o c hai tng tc butan i lch nn ng phn xch o bn hn ng phn trc khong 1,6 ( 1,8 Kcal/mol. Kt qu ny c xc nh bi ph cng hng t ht nhn, nhit thng hn hp cn bng cha 95% CH3 (e) v 5% CH3 (a).

- Khi nhm th l C2H5, isoC3H7 th cu trng xch o vn bn hn cu trng trc.

- Nhm th tertbutyl khc hn nhm ankyl khc, nu But(a) th mt trong ba nhm CH3 bt buc phi hng v vng v gy ra s tng tc vi hai nhm CH2 v tr 3 v 5 c tr s ln hn 5 Kcal/mol. Nng lng ny qu cao nn tertbutyl khng th v tr trc trong cu trng gh nn n ch tn ti v tr xch o.

Nhm tertbutyl trc Nhm tertbutyl xch o

Cu trng ca tertbutyl ciclohexan

b) Ciclohexanol Ciclohexanol tn ti di cu trng vi nhm OH xch o

(6290%)

Cu trng ca ciclohexanol

c) Halogenociclohexan


CH3

CH3

Theo nhiu x in t v nhiu x tia X hay php o momen lng cc, cu trng u i ca clorociclohexan trng thi kh c nguyn t Clor v tr xch o (55%60%). Hiu s nng lng gia hai cu trng l 0,3 0,4 Kcal/mol, chng minh c khong 40% cu trng trc trong hn hp cn bng.

trng thi lng, c hai cu trng trc v xch o u c mt i vi clorociclohexan v bromociclohexan, ph hng ngoi cho bit thm c 40% cu trng trc tn ti trong hn hp cn bng, hiu s nng lng gia cu trng xch o v cu trng trc c c lng l 0,3 0,5 Kcal/mol bi ph cng hng t ht nhn.

Nhm Go Nhm Go CLVT Br I OH OCH3 OCOCH3 OTs SH SPh

0,40 0,50 0,4

0,60,9 0,7 0,7 0,7 0,9 0,8

NH2 COOH COOCH3 CN CH3 C2H5 Pri Bu But Ph

1,21,8 1,2 1,1 0,2 1,7 1,8 2,1 2,1 5,6 3,1

Hiu s nng lng t do cu trng trong ciclohexan mang nhm th ((Go : Kcal/mol)

i vi nhm OH, NH2: tr s nh ng vi dung mi khng cha H+; tr s ln ng vi dung mi c proton.

5.3.3.2. Ciclohexan mang hai nhm th 5.3.3.2.1. Diankylciclohexan

a) Dimetylciclohexan 1,1dimetylciclohexan (ch c mt cu trng)

1,2dimetylciclohexan c ba ng phn cu trng


CH3CH3

CH3

CH3

CH3

CH3 CH3H3C

CH3CH3

CH3CH3

CH3

CH3

CH3

CH3

CH3CH3

CH3

CH3

Trans ee Trans aa

_ Trans ee c mt tng tc butan bn lch ng vi 0,85 Kcal/mol.

_ Trans aa c bn tng tc butan bn lch ng vi 3,4 Kcal/mol

cis ea cis ae Cu trng cis ea c ba tng tc butan bn lch ng vi 2,55

Kcal/mol. nhit thng, 1,2dimetylciclohexan tn ti gn nh

hon ton (99%) di cu trng ee. 1,3dimetylciclohexan c ba ng phn cu trng.

Cis ee Cis aa Trans ea Trans ae

- Cu trng cis ee khng c tng tc butan bn lch. - Cu trng cis aa c mt tng tc nh trc (3,7

Kcal/mol) v hai tng tc butan bn lch (1,7 Kcal/mol) Gaa = 3,7 + 1,7 = 5,4 Kcal/mol

- Cu trng trans ea c hai tng tc butan bn lch ng vi 1,7 Kcal/mol.

1,4dimetylciclohexan c ba ng phn cu trng

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