Nitrogen Compounds, Polymers and Synthesis

Question 1

Why do amines act as bases?

Answer 1

There is a lone pair of electrons on the nitrogen atom of an amine that’s able to accept protons (H⁺).

Question 2

What is formed when amines react with acids?

Answer 2

ammonium salts

e.g. ethylamine, CH₃CH₂NH₂ + HCl → CH₃CH₂NH₃⁺Cl^- (ethylammonium chloride)

Question 3

How do you make amines from haloalkanes and what is the reaction mechanism?

Answer 3

Heat with an excess of ethanolic ammonia (ammonia dissolved in ethanol, so that polar and non-polar reactants both dissolve and mix). Nucleophilic substitution takes place, with the halogen being replaced by an NH₂ group. You can get secondary and tertiary amines by reacting haloalkanes with the primary amine, causing one of the hydrogens in the NH₂ group to be replaced with an alkyl group.

Question 4

Write an equation for the reaction between bromoethane and ammonia, and between ethanamine and bromoethane.

Answer 4

1. 2 NH₃ + CH₃CH₂Br → CH₃CH₂NH₂ + NH₄Br
2. NH₃ + CH₃CH₂NH₂ + CH₃CH₂Br → CH₃CH₂NHCH₂CH₃ + NH₄Br

Question 5

How do you separate the primary, secondary and tertiary amines formed when haloalkanes react with ammonia?

Answer 5

Fractional distillation

Question 6

How do you make an aromatic amine?

Answer 6

Reduce an aromatic compound with a nitro group:

• Reflux the nitro compound with conc. HCl and tin to make a salt
• Add NaOH get the aromatic amine

Question 7

Draw the structure of a primary and a secondary amide.

Answer 7

Question 8

Why do amides undergo different chemical reactions compared to amines?

Answer 8

The carbonyl group pulls electron density away from the nitrogen, so it is less basic.

Question 9

What is an α-amnio acid (give general structural formula)?

Answer 9

• Compound with a carboxylic acid group (COOH) and a primary amino acid group connected to the same carbon.
• The carbon is also bonded to a hydrogen and an R group (which can just be another H).
• RCH(NH₂)COOH

Question 10

Give the structural formulae of the molecules produced when an α-amnio acid reacts with HCl and when it reacts with NaOH.

Answer 10

1. forms a conjugate acid which combines w/ an anion to form a salt:
   
   • RCH(Cl^-N⁺H₃)COOH
2. forms a conjugate base, which combines w/ a cation to form a salt:
   
   • RCH(NH₂)COO^-Na⁺ (+ water)

Question 11

What is formed when an amino acid reacts with an alcohol?

Answer 11

Carboxylic acid group undergoes esterification in presence of a strong acid catalyst, to form an ester.

Question 12

What is a chiral carbon atom?

Answer 12

A carbon atom with 4 different groups attached to it.

Question 13

How do optical isomers interact with light?

Answer 13

They rotate plane polarised light: one enantiomer rotates in the clockwise direction and one rotates in the anti-clockwise direction by the same amount.

Question 14

How can you tell is a carbon on a ring is chiral?

Answer 14

If the order of atoms going around the ring in one direction is different to going around the other direction, they count as different ‘groups’.

Question 15

What are optical isomers?

Answer 15

Molecules with the same structural formula but with non-superimposable mirror images about a chiral centre.

Question 16

Draw the structure of the links in:

1. Polyesters
2. Polyamides

Answer 16

1. -C(=O)O-
2. -N(H)C(O)-

Question 17

What bond breaks during:

1. Polyester base hydrolysis
2. Polyamide acid hydrolysis

and what molecules are formed as a result?

Answer 17

1. C - O (single bond not double)
   
   • dicarboxylic acid salt + diol
2. C - N
   
   • dicarboxylic acid + diamine

Question 18

What monomers can combine to make a polyamide and what part is removed from each?

Answer 18

1. carboxylic acid/acyl chloride and amine on same molecule
2. dicarboxylic acid/diacyl chloride + diamine

H from amine group, OH/Cl from carboxylic acid/acyl chloride

Question 19

What monomers can combine to make a polyester and what is removed from each part?

Answer 19

1. alcohol and carboxylic acid/acyl chlroide on same molecule
2. diol + dicarboxylic acid/diacyl chloride

H from alcohol, OH/Cl from carboxylic acid/acyl chloride