CHAPTER 19 ORGANIC CHEMISTRY II: POLYMERS AND … · Natural rubber: obtained from latex from the bark of rubber tree Artificial rubber: obtained with Z-N catalyst Æ cis-polyisoprene

2009년도 제2학기 화 학 2 담당교수: 신국조 Textbook: P. Atkins / L. Jones, Chemical Principles, 4th ed., Freeman (2008) Chapter 19

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CHAPTER 19 ORGANIC CHEMISTRY II: POLYMERS AND BIOLOGICAL COMPOUNDS

COMMON FUNCTIONAL GROUPS

19.1 Haloalkanes R–X

◈ Nucleophilic substitution reaction

(친핵치환반응,親核置換反應)

C–X bond is polar

Nucleophile replaces X

Ex: OH– ion (– charge), H2O (lone pair)

Hydrolysis in EtOH(aq) solution

3 3CH Br OH CH OH Br− −+ ⎯⎯→ +

19.2 Alcohols R–OH

◆ –OH group, –ol

Ex: CH3OH: methanol (methyl alcohol)

C2H5OH: ethanol (ethyl alcohol)

CH3CH2CH2OH: 1-propanol

CH3CH(OH)CH3: 2-propanol

CH3CH(OH)CH2CH3:

2-butanol or 2-hydroxybutane

Fig. 19.1 The charge distribution in

an ethanol molecule.

Less volatile than alkanes due to hydrogen bonds:

Ex: ethanol(l) vs. butane(g)


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g

◆ Classification of alcohols according to the number of organic groups attached to the C atom

connected to the –OH group:

Primary alcohol: RCH2–OH ex: ethanol

Secondary alcohol: R2CH–OH ex: 2-butanol

Tertiary alcohol: R3C–OH ex: 2-methyl-2-propanol, (CH3)3COH

or tertiary-butyl alcohol or tert-butanol

◆ Synthesis of alcohols Nuclear substitution of haloalkanes

▶ Methanol

2 3

ocatalyst, 250 C,50-100 atm

synthesis gas

CO( ) 2 H ( ) CH OH( )g g+ ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→

Catalyst: mixture of Cu, ZnO, Cr2O3▶ Ethanol

• Fermentation of carbohydrates. • Hydration of ethane

3 42 2 2 3 2

oH PO , 300 CCH =CH ( ) H O( ) CH CH OHg g+ ⎯⎯⎯⎯⎯⎯→

▶ Ethylene glycol 1,2-ethanediol Diol, two –OH groups Antifreeze component Synthetic fiber

1,2-ethanediol, HOCH2CH2OH

19.3 Ethers R – O – R’

3 2 2CH CH O CH CH− − 3 , diethyl ether Lower boiling points than alcohols due to lack of hydrogen bonds

Fig. 19.2 The lower boiling points of ethers than those of alcohols.


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▶ Crown ethers : cyclic ethers, Pedersen (1960)

18-crown-6

(1,4,7,10,13,16-hexaoxacyclooctadecane)

m–crown–n

m: number of atoms in the cycle

n: number of O atoms

Strong binding with metal cations

‘Trojan horse’ for K+ ions

soluble in nonpolar sovents

Ex. KMnO4(crown ether)

18-crown-6

18-crown-6-K

★ Nobel Laureates in Chemistry (1987)

"for their development and use of molecules with structure-specific interactions of high selectivity"

Donald J. Cram Jean-Marie Lehn (美,1919-2001) (佛,1939 - )

Charles J. Pedersen

(美,1904-1989)

出生地: 釜山父: Norwegian marine engineer Steam-ship to far-east (釜山) Worked at Custom service Worked at Unsan mine (平北雲山金鑛, 미국인 채굴권)

母: Japanese

◆ Phenols

▶ Phenol, C6H5OH or Carbolic acid

Weak acid, but stronger than EtOH

Partial oxidation of benzene, Distillation of coal

Toxic: lethal dosage,1g WWII

Reaction with chlorine in tap water foul smell of C6H5Cl

Contamination of Nakdong river in 1991


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▶ Substituted phenols

Essential oils: concentrated, hydrophobic liquids containing volatile aroma compounds from plants.

Thymol: Oil of thyme

Eugenol: Oil of clove

Distillation of herbal plants

Used for cosmetics, perfumes

▶ Resonance structures of phenoxide ion, C6H5O–

←⎯→ ←⎯→ ←⎯→

Conjugate base of phenol stabilizes the anion


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Weaker conjugate base than ethoxide, CH3CH2O–

Phenol is insoluble in water

but soluble in basic solution.

☻ Phenyl methanol, C6H5CH2OH: Benzyl alcohol alcohol, not a phenol

19.4 Aldehydes and Ketones

◆ Aldehyde: –al

▶ Formaldehyde, HCHO methanal

3 2 2o600 C, Ag2 CH OH( ) O ( ) 2 HCHO( ) 2 H O( )g g g+ ⎯⎯⎯⎯⎯→ + g

Destructive effect on bacteria

Wood smoke contains HCHO preservation of smoked foods (훈제,燻製)

“Formalin” : aqueous solution of HCHO preservation of biological specimens

Sick house syndrome (새집증후군,새집症候群)

► Tollens test: ‘Silver mirror’ formation by aldehyde

3 2 Ag (in TolleCH CH C ns rH eO( ) agent)g++

3 2CH CH COOH Ag( )s⎯⎯→ +

Tollens reagent: ammoniacal silver nitrate

[Ag(NH3)2]NO3 (aq)

▶ Acetaldehyde, CH3CHO ethanal

aldehyde ketone Fig.19.3 The results of Tollens test

▶ Aldehydes in essential oils

cherry, almond cinnamon (계피,桂皮) vanilla


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◆ Ketone: –one

▶ Acetone, propanone

Good solvent, miscible with water

Oxidation of secondary alcohol:

CH3CH(OH)CH3(aq) + NaOCl (aq) CH⎯⎯→ 3(CO)CH3 (aq) + NaCl (aq) + H2O (l)

▶ Other ketones:

CH3CH2CH2COCH3, 2-pentanone CH3CH2COCH2CH3, 3-pentanone

☻ No reaction with Tollens reagent

19.6 Carboxylic Acids, R–COOH, -oic acid

▶ Carboxyl group,

◆ Formic acid, HCOOH metanoic acid

◆ Acetic acid, CH3COOH ethanoic acid

▶ Oxidation of primary alcohols and aldehydes with a strong oxidizing agent, acidic KMnO4(aq)

▶ Direct oxidation of alkyl groups to carboxyl group

19.7 Ester, , -oate R C O R || O

− − − '

Product of the reaction between a carboxylic acid and an alcohol

Fragrant odors, flavors of fruits

▶ Ethyl acetate,

ethyl ethanoate


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←⎯→

▶ Benzyl acetate, CH3COOCH2C6H5 Oil of jasmine

▶ Tristearin, C57H110O6 animal fat

Product of the reaction between glycerol and stearic acid, CH3(CH2)16COOH

◆ Condensation reaction

Fig. 19.4 Two molecules are linked in a condensation reaction.

★ Trans fats (트랜스지방脂肪)

► Hydrogenation of oils (ester of cis-unsaturated fatty acids)

saturated fats with higher m. p. : solid, good for baking and extended shelf-life

remaining double bonds converted from cis to trans isomers bad for health!

► Transesterification (에스터교환):

Switching of the long carboxylic acid chains from one alcohol location to another in

a fatty acid by an enzyme. acid catalyst

double bonds remained with high m.p. but no trans fats


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19.8 Amines, Amino Acids, and Amides

◆ Amines: R–NH2 (primary), R–NH–R’ (secondary), |N

/ \(tertiary)

ammonia methylamine dimethylamine trimethylamine

(primary) (secondary) (tertiary)

► Quaternary ammonium ions: tetrahedral structure

Tetramethylammonium ion, (CH3)4N+

Trimethylammonium ion, (CH3)3NH+

► Functional group: amino group, –NH2

► Weakly basic except quaternary ammonium ions

► Foul smell of decaying flesh (along with sulfur compounds)

putrescine, NH2(CH2) 4H2 cadaverine, NH2 (CH2) 5NH2

☻ putrefy : 부패시키다 ☻ cadaver: (해부용)시체(屍體)

◆ Amino Acids NH2 – R – COOH Carboxylic acids containing an amino group (basic) and a carboxyl group (acidic)

▶ Glycine

NH2CH2COOH

α -amino acid

“Zwitterion” in aqueous solution (pH=7): +H3NCH2CO2–

▶ Alanine

CH3CH(NH2)COOH

α -amino acid

+NH3CH(CH2)COOH NH2CH(CH2)COOH (+NH3CH(CH2) CO2–) NH2CH(CH2) CO2–

acidic solution neutral solution basic solution


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Fig. 19.5 The fractional composition of alanine species as a function of pH.

▶ GABA (gamma-aminobutyric acid): 2 2 2 2NH C H C H C H COOHγ β α

γ -amino acid

One of Neurotransmitters (신경전달물질): GABA, Dopamine, Acetylcholine, …

◆ Amide Condensation product of an amine with a carboxylic acid

R – (CO) – NHR’ from a primary amine

⎯⎯→

▶ Mechanism of amide formation

(1) An amine (base) accepts a proton from a carboxylic acid, forming quaternary ammonium salt.

3 3 2 3 2 3CH COOH CH NH CH CO CH NH3− ++ ⎯⎯→ +

(2) Upon heating to 200oC,

Attacking of amine (nucleophile) to the carboxyl carbon Reverse proton transfer

⎯⎯→ ⎯⎯→ ⎯⎯→


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Caprolactam Nylon-6 polyamide

Ex. 19.1 Naming compounds with functional groups

3-methyl-2-butanol 4-chloro-2-pentanone diethylpropylamine

CH3CH(CH3)CH(OH)CH3 CH3CHClCH2COCH3 (CH3CH2) 2NCH2CH2CH3

THE IMPACT ON MATERIALS

◈ Macromolecules

◆ Polymers: chains or networks of small repeating units forming giant molecules

Made by addition reaction and condensation reaction

19.9 Addition Polymerization

◆ Alkenes:

Ex: Ethene (monomer, repeating unit) Polyethylene, – (CH2CH2)n –

◆ Substituted ethene monomer, CHX=CH2

X=Cl : CHCl=CH2, vinyl Polyvinyl chloride (PVC), – (CHClCH2)n –

X=CH3 : CH3CH=CH2, propene Polypropylene, – (CH(CH3)CH2)n –


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◆ Radical polymerization

● Initiation: ● Propagations:

● Termination: no more monomers, linkage of two radical chains

★ Problem ! : Random orientation and side-chain growth of polypropylene Poor packing

▶ Ziegler-Natta catalyst : TiCl4 + (CH3CH2)3Al

Fig. 19.6 Substituents in a polymer with (a) random and (b) stereoregular (with Z-N catalyst) orientations.


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★ Nobel Laureate in Chemistry (1963) "for their discoveries in the field of the chemistry and technology of high polymers"

Karl Ziegler Giulio Natta

(獨,1898-1973) (伊,1903-1979)

● Ziegler: organoaluminum compound catalyst

control polymerizations and to obtain molecular chains of the required length

● Natta:

a certain Ziegler catalyst leads to a steroregular isotactic polymer High-density polymer

The floating PE, produced from

high pressure polymerization.

The bottom one, produced with a Z-N catalyst.

Fig. 19.7 The two samples of polyethylene in a test tube.

▶ Rubber: a polymer of isoprene

Isoprene

Fig. 19.8 Collecting latex from a rubber tree.

► Natural rubber: obtained from latex from the bark of rubber tree ► Artificial rubber: obtained with Z-N catalyst cis-polyisoprene

Naturally occurring material, “gutta-percha” (a plant’s name in Malay, “getah perca”) trans-polyisoprene (golf ball, filling dental canals)


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Fig. 19.9 (a) Natural rubber (all cis) (b) “Gutta percha” (all trans)

19.10 Condensation Polymerization ◈ Condensation polymers ◆ Polyester: Condensation of monomers with carboxyl group and those with hydroxyl group ▶ Dacron (or Terylene) : polyethylene terephthalate

esterification of terephthalic acid with ethylene glycol (1) first step

(2) second step: further condensations

a new ethylene glycol carboxyl group of the product another phthalic acid hydroxyl group of the product

…………………………………… (3) Final product

☻ Condensation polymerization : growth of chain occurs only at functional groups

chain branching less likely ! good synthetic fibers

Fig. 19.10. Synthetic fibers through Fig.19.11 A scanning electron micrograph of a spider’s spinneret (방적돌기,紡績突起) Dacron polyester and cotton fibers.


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◆ Polyamides : Condensation polymerization of amines with carboxylic acids

▶ Nylon-66 : Wallace Carothers (DuPont, 1935)

a polymer of 1,6-diaminohexane, H2N(CH2)6NH2, and adipic acid, HOOC(CH2) 4COOH

(1) Formation of “nylon salt”

HOOC(CH2) 4COOH + H2N(CH2)6NH2 –O2C(CH2) 4CO2– + +H3N(CH2)6NH3+

(2) Condensation upon heating “nylon salt”

+

⎯⎯→ + H2O

Fig.19.12 A crude nylon fiber.

Upper layer: an acid dissolved in hexaneBottom layer: an aniline salt dissolved in water

Interface: formation of polymer pulled out in a long string

(3) Further condensation leads to…

Fig. 13 The strength of nylon fibers comes from the hydrogen bonds between neighboring polyamide chains

Ex. 19.2 Determining the formulas of polymers and monomers

Write the formula of (a) the monomer of Kevlar, a strong fiber for bullet-proof vests:


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(b) two repeating units of the polymer that is formed when peroxides are added to

CH3CH2CH=CH2 at high temperature and pressure.

[Solution]

(a) Two amide groups face in opposite directions

Polyamide formed from two different monomers:

One with two acid groups and the other with two amine groups

(b) The monomer is an alkene. forming an addition polymer

Self-Test 19.4A

(a) Write the formula for the monomer of Teflon, – (CF2CF2)n – . CF2=CF2

(b) Write the formula for the polymer of lactic acid, CH2CH(OH)COOH

[Solution] (a) CF2=CF2

(b) – (OCH(CH3)CO)n –, biodegradable polymer, surgical sutures (봉합사,縫合絲)

Self-Test 19.4B

(a) Write the formula for the monomer of Poly(methyl methacrylate), PMMA.

(b) Write the formula for the two repeating units of polyalanine,

the polymer of the amino acid alanine, CH3CH(NH2)COOH


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[Solution] (a) Monomer: CH2=C(CH3)COOCH3

(b) Monomer: CH3CH(NH2)COOH

Polyalanine

19.11 Copolymers and Composites ◆ Copolymers (공중합체,共重合體): Polymers made up of more than one type of repeating units

Fig.19.14 The classification of cop[olymers

▶ Alternating copolymer

Nylon-66: 1,6-diaminohexane, H2N(CH2)6NH2 / adipic acid, HOOC(CH2)4COOH

▶ Block copolymer

Polystyrene: transparent, brittle

Polybutadiene: synthetic rubber, resilient, soft, opaque

● Poly(styrene/butadiene): high-impact polystyrene, strong, transparent

Styrene-butadiene rubber (SBR): tires, shoes, chewing gums

▶ Random copolymer: random linkage of different monomers

► Graft copolymer: Long chain of one monomer with shorter chains of the other monomer

attached as side groups

Hard contact lens: nonpolar hydrocarbon repelling water

Soft contact lens: backbone of nonpolar monomers with side groups of different

water-absorbing monomers (50% volume of lens)


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◆ Composite materials (복합재료) ► Bone tissue: low density, strength

Crystals of phosphate salts embedded in fibers of a natural polymer, collagen ► Mollusk (연체동물) shell:

Flat crystals of CaCO3 embedded in a tough, flexible organic matrix.

Fig.19.15. The mollusk shell of the mother-of-pearl. Fig.19.16. A mollusk shell design for an F1 car.

19.12 Physical Properties of Polymers ► Average molar mass, Average chain length ► No definite m.p.

Gradual softening with temperature Glass transition temperature, Tg► Viscosity of molten polymer chain length ∝► Mechanical strength

Longer chain length Properties of functional groups

Affect the strength of intermolecular forces Chain packing arrangements

Unbranched chain polymers are strong ▶ Elasticity

Natural rubber: low elasticity “Vulcanization(가황,加黃)” increases elasticity Too many cross-linking hard “ebonite”

Fig.19.17 The cross-links between polyisoprene chains.

BOX 19.1 FRONTIERS OF CHEMISTRY: CONDUCTING POLYMERS

★ Nobel Laureates in Chemistry (2000) "for the discovery and development of conductive polymers"

Alan J. Heeger (美,1936 – )

Alan G. MacDiarmid (美/新西蘭,1927-2007)

Hideki Shirakawa 변형직(邊衡直)박사 (日,1936 – )


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▶ Polyacetylene

Flexible polyacetylene film

Oxidation of polyacetylene with iodine increases the conductivity by 10 million times.

sp2 hybrid C atoms, alternation of double and single bonds

delocalization of electrons along the entire chain

▶ Polypyrrole:

Smart windows: transparent yellow-green

light⎯⎯⎯→ opaque blue-black

Radar camouflage cloth: absorbing microwaves

▶ Polyaniline:

Flexible coaxial cable

Rechargeable, flat, button-like batteries

Laminated, rolled films for TV screens

▶ Poly-p-phenylenevinylene (PPV)

Electroluminescent

Multicolor light-emitting LED

THE IMPACT ON BIOLOGY 19.13 Proteins : Condensation copolymers of ~20 different naturally occurring amino acids

◈ 9 Essential amino acids: to be ingested to our body by diet

histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine


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◆ Peptide:

Condensation product of two or more amino acids

Peptide bond: –CO–NH–

Residue: each monomer used to form a peptide Ex: Gly-Ala

► Oligopeptide: a few amino acids residues present

Ex: Aspartame: artificial sweetener, dipeptide (with 2 residues)

◈ Structure of proteins

▶ Primary structure: sequence of residues in the protein chain

► Aspartame: Phe-Asp (phenylalanine and aspartic acid)

► Human hemoglobin:

Leu-Ser-Pro-Ala-Asp-Lys-Thr-Asn-Val-Lys-… …-Val-Lys-Gly-Trp-Ala-Ala-… …-Ser-Thr-Val-Leu-Thr-Ser-Lys-Ser-Lys-Tyr-Arg ☻ Modification of the primary structure congenital desease

Fig. 19.18 Sickle-shaped red blood cells due to Glu Val.


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▶ Secondary structure: shape adopted by the polypeptide chain (how it coils or forms sheets) ► α -helix : helical conformation held in place by hydrogen bonds

Fig. 19.19 A representation of an α -helix

► β -sheet: side-by-side arrangement to form nearly flat sheets, ex: silk ► Alternating α -helix and β -sheet:

Fig. 19.20 One of the four polypeptide chains that make up the human hemoglobin molecule.

α -helix and β -sheet. The chains consist of alternating regions of

▶ Tertiary structure:

► Folded shape of secondary structure due to interactions between residues (e.g. –S–S– link)

► Globular form of each chain in hemoglobin

► Incorrect folding: Alzheimer’s disease,

“Prion disease” – Mad cow disease (variant Creutzfeld-Jakob disease)

Fig.19.21 Formation of α -helix and β -sheet and folding of coils and sheets to form the shape of protein.

(a) Newly formed polypeptide; (b) intermediate; (c) subunit; (d) mature (dimeric) protein.


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▶ Quaternary structure:

► Stacking together of neighboring polypeptide chains in a specific arrangement

► Quaternary structure of four polypeptide chains of hemoglobin

Fig. 19.22 The spider web. Fig. 19.23 The artificial spider silk.

19.14 Carbohydrates (탄수화물,炭水化物)

▶Usual empirical formula, CH2O

▶Sugars (glucose/aldehyde, fructose/ketone)

▶Contain many –OH groups

alcohols, hydrogen bonds

◆ Polysaccharides: Polymers of glucose

▶ Starch

► consists of two components: amylose and amylopectin

► amylase: makes up 20~30% of starch, several thousand glucose units

► amylopectin: branched large structure, million glucose units

Fig. 19.24 The amylase molecule, one component of starch, is a polysaccharide.


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Fig. 19.25 The highly branched large amylopectin molecule

▶ Cellulose : ► the same glucose monomer units but with linked differently

► flat, ribbonlike strands hydrogen bonds

Fig. 19.26 (a) Cellulose, a polysaccharide of glucose units linked together to form long, flat ribbons that can produce a fibrous material through hydrogen bonding. (b) Long tubes of cellulose form the structural material of an aspen tree.

19.15 Nucleic Acids

◈ DNA (Deoxyribonucleic acid)

► Production of protein

► Carry genetic information to the next generation

► Ribose

Fig. 19.27 A DNA molecule (~2m) spilled out of a damaged cell of a bacterium.


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▶ Deoxyribose

▶ Bases (amines): A, G, C, and T (DNA) or U(RNA)

▶ Nucleoside: sugar (deoxyribose) + base attached to C1

▶ Nucleotide: sugar (deoxyribose) + base attached to C1 + phosphate at C5


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▶ Nucleic acid : Product of condensation of nucleotides

Fig. 19.28 The condensation of nucleotides leading to the formation of a nucleic acid.

◈ Double helical structure of DNA: hydrogen bonds between A=T and G≡C

Fig. 19.29 The base pairings by hydrogen bonds(A=T and G≡C) leads to double helical structure of DNA.

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CHAPTER 19 ORGANIC CHEMISTRY II: POLYMERS AND … · Natural rubber: obtained from latex from the bark of rubber tree Artificial rubber: obtained with Z-N catalyst Æ cis-polyisoprene