27 Amines, Amino acids and Proteins

primary, secondary, tertiary, quaternary amines

methods of preparing amines

1. haloalkane → amine / secondary amine (only aliphatic)

2. reduction of nitrobenzene

3. reduction of nitriles

haloalkane → amine (only aliphatic) reactants and conditions

• XS NH3 (alcoholic)

• warm (can be reflux)

why can’t NH3 be in water / why does it have to be alcoholic

water is a nucleophile so will react with haloalkane

mechanism for haloalkane → amine

haloalkane → 2° amine reactants and conditions

• XS alcoholic CH3-NH2(alcoholic) (mainly get 2°)

or

• XS R-Br (mainly get 3°/quaternary amine)

can bromo benzene turn into an amine?

no

because the carbon is δ+

reduction of nitrobenzene reactants and conditions

• Sn (s)

• conc H2SO4(aq)

• heat under reflux

equation for reduction of nitrobenzene

reduction of nitriles → 1° amine reactants and conditions

• H2

• Ni catalyst

• (heat under reflux)

reduction of nitriles → 1° amine equation

general formula of an alpha amino acid

RCH(NH₂)COOH

what can amines behave as in reactions

• nucleophiles (e- pair donors, lone pair on N)

• weak base (a proton acceptor: lone pair on N, can donate to a H+)

which is more basic, phenylamine or methylamine

methylamine

basicity from phenylamine to trimethylamine

strongest base:

• positive inducing effect of alkyl groups

• donates e- density to the N

• causing its lone pair of e- to become more available

weakest base

• nitrogen’s lone pair of e- become delocalised in the benzene ring

• therefore less available

structure of phenylamine + effect on reactivity w/ electrophiles

• lone pair in a p-orbital overlaps with C p-orbitals

• so lone pair of N delocalises into π ring

• 8πe- spread over 7 atoms

• more reactive to electrophilic attack

• higher e- density in the ring attracts e-philes more strongly

• polarises electrophiles so don’t need catalyst

approximately how many naturally occurring a-acids are there

22

• all are apha a-acids

isoelectric point def

pH when the overall compound is neutral where the positive and negative charges cancel out

when the zwitterion is formed

what does lysine look like

reactions of a-acids

as an amine

• amide (w/ acyl chloride)

• salt (w/ acid)

• 2° amine (w/ haloalkane)

as a c-acid

• ester (+alcohol + conc. H2SO4 + reflux)

• acid anhydride (dehydrate it)

• acyl chloride (+ SOCl2)

• salt (+Na, NaOH, Na2CO3)

how are amides formed

acyl chlorides + ammonia

ethanamide formation balanced equation

structures of primary, secondary and tertiary amides

stereoisomerism def

Compounds w the same structural formula but a different arrangement of atoms in space

optical isomerism

• found in molecules that contain a chiral centre

• which leads to the existence of two non-superimposable mirror image structures

  • these 2 molecules are known as optical isomers or enantiomers

chiral centre

a (carbon) atom that is attached to four different atoms or groups of atoms

how to draw optical isomers

• must show 3D tetrahedral arrangement of the 4 diff grps around the central chiral C atom

• mirror

how to name primary amides

• add ‘-amide’ to the stem name

• e.g. ethanamide

how to name secondary amides

• the alkyl chain attached to the nitrogen is added at the start of the chemical name

• this alkyl chain is prefixed with N-

• e.g. CH₃CONH(C₃H₇)

  • propyl group on the nitrogen (N-propyl)

  • two carbons with a C-C (ethan-) and an amide group (-amide)

• N-propylethanamide

how to name tertiary amides

• 2 alkyl chains attached to the nitrogen

• same with secondary amides

• chains are listed in alphabetical order w/ ‘di-’ if needed

• e.g. CH₃CONHCH₃(C₃H₇)

  • N-methyl

  • N-propyl

  • ethan-, -amide

• N-methyl-N-propylethanamide

E/Z isomerism

• Arises around double bonds due to restricted rotation due to pi-bonds.

• Therefore groups attached to each carbon atom are fixed relative to each other.

• A molecule has E/Z isomerism if it has both a:

  • A C=C double bond

  • Different groups attached to each carbon atom of the double bond

cis trans isomerism

A special case of E/Z isomerism.

• Must have a C=C double bond

• Each carbon in the double bond must be attached to two different groups

• One of the attached groups on each carbon atom of the double bond must also be the same.

acid hydrolysis of amides

• heat under reflux

• 2moldm-3 HCl(aq)

base hydrolysis of amides

• heat under reflux

• 2moldm-3 NaOH(aq)

• then acidify (+HCl)

difference/similarities between enantiomers (L or D)

• chemically they are the same

• only difference is they rotate plane polarised light in different directions

  • other than enzyme reactions, all naturally occuring a-acids are L enantiomers (only enzymes accept L in active site)

what is a racemic mixture

• an equal mixture of 2 enantiomers

• doesn’t rotate plane polarised light

how to prevent a racemic mixture forming

• using enzyme reactions

• making sure molecule is only attacked by 1 side

Sometimes it is difficult to manufacture a drug containing only the one pharmocologically active stereoisomer. Describe two possible disadvantages of producing a drug containing a mixture of several stereoisomers. (2)

1. drug effectiveness: sometimes only one enantiomer is responsible for the drug’s beneficial effects whereas the other one is either less effective/has no effect

2. drug safety: the other enantiomer can have harmful/the opposite effect of the enantiomer meant to be working

condensation polymerisation def

the joining of lots of small monomers with the loss of a small molecule, (usually water or hydrogen chloride).

Two different functional groups are needed.

what can condensation polymers be formed by

• Dicarboxylic acids and diols

• Dicarboxylic acids and diamines

• Amino acids

  

hydrolysis def

breaking down of a compound using water

what is nylon used for

clothing - jumpers/tights

guitar strings

what is polyester used for

fleeces

addition vs condensation polymerisation

addition

• alkenes

• C=C

• breaking π bond

• making 2x C-C between monomers

condensation

• 2 diff functional groups

• ester/amide links are biodegradable

• 2 products

Type	Characteristics	Example of monomer(s)
Addition polymerisation	Monomer contains a C=C double bond Backbone of polymer is a continuous chain of carbon atoms	ClCH=CHCH3
Condensation polymerisation	Two monomers, each with two functional groups One monomer with two different functional groups Polymer contains ester or amide linkages	HOOCCH2COOH and HOCH2CH2OH H2NCH2COOH

what’s another name for terylene

• dacron

• poly(ethylene terephthalate)/ PET

what’s terylene used for

cushions and other soft products

what are polyamides

monomers for polyamides

• • 

how is a dipeptide formed

• polymerising 2 amino acids together

• The amine group (-NH2) and acid group (-COOH) of each amino acid is used to polymerise with another amino acid

hydrolysis of condensation polymers

hydrolysis of polyamides

what is Nomex

a synthetic heat and fire-retardant polyamide used in oven gloves

why is the fact polyesters and polyamides can be broken down using hydrolysis an advantage over addition polymers?

This is because when they're taken to landfill sites, they can be broken down easily and their products used for other applications.

show how ethylamine, C₂H₅NH₂, acts as a base (4)

describe and explain the effect on the basicity when the primary amine group is attached to a benzene ring, using phenylamine as an example (3)

• lone pair on N atom delocalises into the delocalised πe- ring

• so e- density on N decreases

• weaker base, less likely to donate e- to H+

explain the relative basicities of ethylamine and phenylamine

ethylamine

• lone pair of e- on N atom

• has an alkyl group attached which is slightly e- donating

• so e- density increases on N atom

• more likely to donate e- to H+

• so a proton acceptor, more basic

phenylamine

• lone pair of e- on the N atom delocalises into benzene ring

• so e- density decreases

• less likely to donate e- to H+

• so less basic than ethylamine

a sample of benzocaine was warmed in dilute HCl for an hour

draw the structures of the two organic products formed in these acidic conditions

explain the term ‘secondary amine’ (1)

(an organic compound w/) a N atom bonded to 2 alkyl groups

why is lysine described as an alpha amino acid (2)

• the amine group is attached to the 2nd carbon atom next to the carboxyl group

describe the structural feature in the lysine molecule that results in the property of optical isomerism

4 diff groups around a carbon

identify the new functional group formed in rxn 2 (1)

• secondary amide group

state, with a reason, the type of polymerisation that would be used to form polymer A

condensation because there’s the loss of a small molecule

reactions w/ water:

• aliphatic amines are very soluble (1) forming alkaline solutions

• RNH2 + H2O → RNH3+OH-

• aromatic amines are only slightly soluble

reactions w/ acids/bases

• all amines react readily (1) forming salts

• RNH2 + HCl → RNH3+Cl-

• aliphatic amines react as nucleophiles (1) w/ e.g. haloalkanes

• RNH2 + CH3Cl → RNHCH3 + HCl

suggest a reason why many polyesters and polyamides are degradable while poly(alkenes) are not (3)

substances w ester/amide linkages can be metabolised and broken down by microorganisms, unlike poly(alkenes) which have a C-C back bone

(just the purification)

Tartatric acid, shown below, is an organic acid present in fruit juice. Write the systematic name

2,3 - di hydroxy butane di oic acid