organic chemistry-jee

8/13/2019 organic chemistry-jee

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SECTION IV Subjective Questions

LEVEL I

1. An organic compound (A) C6H10on reduction, first give (B) 6 12C H and finally (c) 6 14C H

. (A) on reaction with ozone followed by hydrolysis in presence of Zn gives two

aldehydes 2 2 2C H O (E). Oxidation of (B) with acidified 4KMnO gives acid (F) 3 6 2C H O .

Determine structures of (A) to (F) with proper reasoning.

2. Identify (a) the chiral compound C, 10 14C H , that is oxidized with alk. 4KMnO to

PhCOOH, and (b) the achiral compound D, 10 14C H , inert to oxidation under the same

condition.

3. An alkyl halide, (X), of formula 6 13C H Cl on treatment with potassium tertiary butoxide

gives two isomeric alkenes Y and Z 6 12(C H ) . Both alkenes on hydrogenation gives 2, 3-

dimethylbutane. Predict the structures of X, Y and Z.

4. a)2

Br (A)

CH3

HPh

H

HBr/peroxide

(B)

Identify A and Bb) Write the product(s) of the following reactions:

Peroxide

3 2 3CH CH CH BrCCl ?

5. Write the major products of the hydroboration and oxidation of:

a) 1-Ethyl cyclopentene

b) Methylene cyclopentene.

6. Give the missing compounds in the following:

a)3 3BH .THF CH COOH? ?

b) 3 3BH .THF CH COOH? ? c) 3 3BH .THF CH COOH? ?

d)

3

3

( i)BH .THF

(ii)CH COOH?

7. Complete the following equation:

a) 2 2H H

3 3 3 2 2 3Pt PtCH C CCH (A) CH CH CH CH

b) 2 5Na C H OH

3 3 2 5CH C CCH (B) NaOC H

8. a) Starting with any alkyne, prepare ethyl cyclohexyl ethyne.b) Starting with cyclohexyl ethyne, prepare acetyl cyclohexane.


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is reductively ozonized to 2Me C O . Give the structures of (l) and (J) and explain the

formation of the latter.

5. a) Identify X, Y and Z in the following sequence of reactions giving stereo chemical

structures wherever possible.

3 32

4 2

( i) CH CO H(i )H(i) Na(ii) Br Pd BaSO (ii) H / H OC CH (X) (Y) (Z)

b) Complete the following sequences

i)3AlCl

3 2 2C H C H C H C l

ii) 2 2

3

Br i) NaNH (3 equi.)

6 5 2 ii )CH IC H CH CH A B

6. Hydrocarbon (A) C6H10 on treatment with H2/Ni, H2/Pd BaSO4 and Na/liquid NH3

forms three different reaction products (B), (C) and (D) respectively. (A) does not form

any salt with ammoniacal AgNO3 solution but forms a salt (E) on heating with NaNH2in

an inert solvent. Compound E reacts with CH3I to give (F). Compound (D) on oxidativeoznolysis gives n-butanoic acid along with another product. Give structures of (A) to (F)

with proper reasoning.

7. A hydrocarbon (A) containing 90% carbon reacts with dil. H2SO4in presence of HgSO4

to give (B). Compound (B) is reduced by LiAlH4 to (C) which on heating with H2SO4

gives (D) directly by hydrogenation in presence of deactivated Pd-CaCO3 catalyst.

Outline the reactions.

8. Identify the missing compound in the following sequence of reaction:i) 2 2 2 2H O H Br NaNHKOH( alc.)

2 Lindlar's catalystHCaC (A) (B) (C) (D) (E)

ii)

22 4 2 4 2

2

2

4H O LiAlH Conc. H SO Br H / Hg

2 3 H O

NaNH

Mg C (A) (B) (C) (D)

(E) (F)

iii) 2 2 4 4Br / h Br / CCl KMnOalcoholic KOH alcoholic KOH

3 2 2 3 1 mol HCH CH CH CH A B C D E

9. An hydrocarbon (A), C8H14, decolourises Br2/CCl4and cold dil. neutral KMnO4solution,

but does not react with ammonical AgNO3 and Cu2Cl2 solutions. It on ozonolysis

produced two molecules of the same acid (B), C4H8O2, which on heating with sodalimegave propane. What are (A) and (B) ?

10. A hydrocarbon (A) is treated with excess of HCl to give a dihalogen

compound (B), Subjective

Problem 1: 2-Butyne undergoes following reactions in steps as indicated. Identify A to H.


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2 2

2

H D / Pt

3 3 Ni B(P2)CH C CCH A B

2D / PtNa/ EtOH C D

2 2

2

H Br

Ni B(P 2)E F

2 2Br H

NiG H

Solution:A is obtained by syn addition A =

CH3

H H

CH3

cis

B is also obtained by syn addition B =

meso

CH3

H

D D

H

CH3

C is obtained by anti addition C =

H

CH3 H

CH3

D is mix of d- and l- (reacemic mixture) D =

d- and l-(racemic)

CH3

H

D H

D

CH3

E is obtained by syn addition E = as A

Addition of 2Br is anti F =

racemic

CH3

H

Br H

Br

CH3

G =

CH3

Br CH3

Br

H = as F

Problem 2: 3(l)Li, NHn BuC CMe A 4 2dil .KMnO /H O

3 2HCO H / H O2H

Lindlar's catalystB

C

Identify A, B and C with proper explanation.


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Solution:

n - BuC C H

H CH3

n - BuC C H

CH3 HA-trans

B-cis

3HCO H

Li,

3NH

2H

Lindlar's catalyst

(by anti addition) (by syn addition)

OH

CH3

H

H OH

n-Bu(C) - and its enantiomer (racemic)

n BuC CMe

4KMnO

Problem 3: One mole of a hydrocarbon (A) reacts with one mole of bromine giving a dibromo

compound 5 10 2C H Br . Substance (A) on treatment with cold, dilute alkaline

4KMnO solution forms a compound 5 12 2C H O . On ozonolysis (A) gives

equimolar quantities of propanone and ethanal. Deduce the structural formulaof (A).

Solution: 32

i) O

ii) HA Propanone + ethanal

So, A is

CH3

CH3

CH32-methylbut-2-ene

CH3

CH3


2Br CH3

CH3

Br

Br

CH3

2,3-dibromo-2-methylbutane

CH3

CH3


4alk. KMnO CH3

CH3

OH

CH3

OH

2-methylbutane-2,3-diol


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Problem 4: An unsaturated hydrocarbon A 6 10(C H ) readily gives B on treatment with

2NaNH in liquid 3NH . When B is allowed to react with 1-chloropropane a

compound C is obtained. On partial hydrogenation in the presence of Lindlar

catalyst, compound C gives D 9 10(C H ) . On ozonolysis D gives 2, 2-dimethyl

propanal and 1-butanal. With proper reasoning give the structures ofA, B, C and D.

Solution:

A = CH3

CH3

CH3

H

B = CH3

CH3

CH3

C Na

C = CH3CH3

CH3

CH3

D = CH3

CH3

CH3

CH3

Problem 5: A compound (X) when passed through dil 2 4H SO containing 4HgSO gives a

compound (Y) which on reaction HI and red phosphorous gives 2 6C H . The

compound (X) is?

Solution: The compound (X) is likely to be alkyne which reacts with water in presence of

2 4H SO and 4HgSO as catalyst to form a carbonyl compound. HI and red

phosphorous can reduce a carboxyl compound to alkane having same number of

carbon atoms.

Therefore (Y) is likely to be acetaldehyde which is the hydration product of

ethyne2 4

4

H SO

2 2 3HgSOX (Y)

HC CH H O [CH CH OH] CH CHO

red P

3 3 3 2 2CH CHO 4HI CH CH 2I H O

Problem 6: What is the major product by the addition of HCl to 2, 2, 2-trichloropropene?

Solution: 3CCl is a strongly electron withdrawing group. The addition of HCl to >C=C

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