Amines, amides, amino acids, & proteins - Organic Chem III

Question 1

What are amines derivatives off?

Answer 1

Ammonia - NH3

Question 2

What do aromatic amines look like?

Answer 2

The N atom directly attached to the benzene ring
Eg/ phenylamine

Question 3

Why do primary and secondary amines have relatively high melting and boiling points?

Answer 3

A lot of energy is needed to overcome the hydrogen bonds, dipole-dipole forces and London forces between the molecules
N.B. tertiary amines cannot form hydrogen bonds as they don’t have a hydrogen directly attached to the nitrogen

Question 3

Why are amines soluble in water?

Answer 3

All amines can hydrogen bond with H2O molecules, as the lone pairs of electron on the N atom can hydrogen bond with the positive dipole Hs of H2O

Question 4

Why does solubility in water decrease as the size of the alkyl chain increase?

Answer 4

Alkyl groups are non-polar/hydrophobic
Solubility decreases as the proportion of the molecule that can form hydrogen bonds decreases

Question 5

What smell do amines have?

Answer 5

Fishy smell
Vapours turn damp red litmus paper blue

Question 6

What is the order of basicity?

Answer 6

Most basic: 3° > 2° > 1° > NH3 > aromatic least basic

Question 7

Can this order of basicity be explained?

Answer 7

Alkyl groups are electron releasing. The greater the number of alkyl groups attached to the N atom, the greater the electron density on the N atom, so the lone pair can more readily accept a H+

The lone pair of electron on the N atom is at the correct orientation to overlap with the delocalised π system of the benzene ring. The lone pair of electrons is therefore not localised on the N atom, and is less able to accept a H+

Question 8

Which is the stronger base, methylamine or diethylamine?

Answer 8

Diethylamine
- More alkyl groups attached to the N atom, the greater the electron density on the N atom, so the lone pair can more readily accept a H+

Question 9

Which is the stronger base, ammonia or phenylmethylamine?

Answer 9

Phenylmethylamine
- Alkyl groups are electron releasing. The greater the number of alkyl groups attached to the N atom, the greater the electron density on the N atom, so the lone pair can more readily accept a H+

Question 10

What is the reaction between ethylamine and hydrochloric acid

Answer 10

C2H5NH2 + HCl -> C2H5NH3Cl

Question 11

How could you liberate the free amine from the salt?

Answer 11

Add NaOH

Question 12

What is the test for NH4+?

Answer 12

NH4+ + OH- –> (warm) NH3 + H2O
- pungent smell, damp red litmus paper blue

Question 13

What does the SN1 mechanism look like?

Answer 13

Favoured by tertiary halogenoalkanes
1. The first NH3 acts as a nucleophile
2. The second NH3 acts as a base (a proton acceptor)

Question 14

What does the SN2 mechanism look like?

Answer 14

Favoured by primary halogenoalkanes

Question 15

Why is there a problem with this reaction?

Answer 15

The amine produced can also act as a nucleophile
- You end up with a mixture of liquid products - so you’d separate them by fractional distillation

Question 16

What is a more controlled method of preparation of a primary aliphatic amines to reduce a nitrile?

Answer 16

Eg/ CH3C≡N + 2H2 –> (Ni catalyst, 150) CH3CH2NH2
Eg/ CH3C≡N + 4[H] –> (LiAlH4 in dry ether, room temp.) CH3CH2NH2

Question 17

Why can’t the above methods be used to prepare an aromatic amine?

Answer 17

The ammonia, with its lone pair of electron will be repelled by the electron rich benzene ring

Question 18

How could you produce an aromatic amine?

Answer 18

To produce an aromatic amine - use tin in conc. HCl, heat under reflux
Nitrobenzene + 6[H] –> phenylamine + 2H2O

Question 19

What is the reaction between ethanoyl chloride and butylamine:

Answer 19

Eg/ butylamine + CH3COCl –> N-butylethanamide + HCl

Question 20

What is the reaction between phenylamine and ethanoyl chloride:

Answer 20

Eg/ phenylamine + CH3COCl –> N-phenylethanamide + HCl

Question 21

What are polyamides formed by?

Answer 21

Results from the condensation of diacylchlorides (or dicarboxylic acids) and diamines to form the substituted amine group

Question 22

What is a copolymer?

Answer 22

A copolymer results when a diacyl chloride reacts with a diamine to form repeating substituted amide groups. The monomers each have two functional groups (bifunctional)

Question 23

What are amino acids?

Answer 23

Compounds that contain both a basic -NH2 group and an acidic -COOH group. Amino acids are the chief constituents of proteins.
NH2CH(R)COOH

Question 24

Why are amino acids chiral?

Answer 24

Attached to 4 groups. With the exception of the simplest amino acid, glycine, all amino acids show optical activity. Therefore each amino acid can exist in two forms that are non-superimposable mirror images of each other.

Question 25

What are the physical properties of amino acids?

Answer 25

• Solids with relatively high melting points
• Soluble in water but have low solubility in non-polar solvents
• Exists as zwitterions (internal salts): a lot of energy is needed to overcome the strong electrostatic forces of attraction between the oppositely charged ions in neighbouring zwitterions

Question 26

What is the reaction of amino acid with acid (H+):

Answer 26

NH2CH2COOH + H+ –> NH3+CH2COOH

Question 27

What is the reaction of amino acid with base (OH-):

Answer 27

NH2CH2COOH + OH- –> NH2CH2COO- + H2O

Question 28

What is the reaction of amino acid undergoing esterification with ethanol (and conc. H2SO4)

Answer 28

NH2CH2COOH + CH3CH2OH ⇌ NH2CH2COOCH2CH3 + H2O

Question 29

What is the reaction of amino acid undergoing acylation with ethanoyl chloride

Answer 29

NH2CH2COOH + CH3COCl –> CH3CONHCH2COOH + HCl

Question 30

How can a dipeptide be formed?

Answer 30

A didpeptide is a dimer formed from two amino acids
CONH - peptide bond

Question 31

How do you hydrolyse a peptide?

Answer 31

This is done by refluxing with hydrochloric acid to break down the peptide bonds

Question 32

How can peptides and proteins be hydrolysed into their constituent amino acids?

Answer 32

By adding conc. HCl
Then individual amino acids can then be separated using either paper chromatography or TLC

Question 33

What does the rate at which a compound moves up the TLC plate depend on?

Answer 33

Its solubility in the chosen solvent. Each compound within a mixture would have a different solubility so they separate as the solvent moves up the plate