Chapter 27

Question 1

What are amines?

Answer 1

• Compounds derived from ammonia, where one or more of the H atoms are replaced by a carbon chain

Question 2

In what 2 ways can amines be classified?

Answer 2

• Primary, secondary and tertiary
• Aliphatic or aromatic

Question 3

What are aliphatic and aromatic amines?

Answer 3

• In aliphatic amines the N atom is attached to at least one straight or branched carbon chain
• In aromatic amines the N atom is attached to an aromatic ring

Question 4

What are primary, secondary and tertiary amines?

Answer 4

• A primary amine is bonded to 1 alkyl or aryl groups
• A secondary amine is bonded to 2
• A tertiary amine is bonded to 3

Question 5

How are primary amines named? Give examples.

Answer 5

• If the amine is at the end of the chain, you add the suffix -amine (e.g. ethylamine)
• If the amine is not on carbon 1, you use the prefix amino- (e.g. 2-aminobutane)

Question 6

How are secondary and tertiary amines named?

Answer 6

• If they’re attached to multiples of the same alkyl chain, you use the prefix di- or tri- (e.g. dimethylamine)
• If they’re attached to different alkyl chains, use the short one as a prefix (if there are 2 other chains, put them in alphabetical order) and add an N to show that the other chain is also bonded to the nitrogen atom (e.g. N-methylpropylamine, N-ethyl-N-methylpropylamine, N,N-dimethylethylamine)

Question 7

What can amines can act as in chemical reactions?

Answer 7

• Weak bases, as the lone pair on the N atom can accept a proton and form a dative covalent bond
• Nucleophiles, as there is a lone pair of electrons on the N atom

Question 8

How do amines react with acids? Give an example.

Answer 8

• They form an ammonium salt
• Hydrochloric acid + propylamine -> propylammonium chloride

Question 9

How can primary amines be prepared?

Answer 9

• Salt formation: reacting a haloalkane with ammonia to form an ammonium salt
• Amine formation: reacting the ammonium salt with sodium hydroxide to form the primary amine

Question 10

How are secondary and tertiary amines formed?

Answer 10

• To form secondary amines, the process to form primary amines repeats, but with a primary amine taking the role of ammonia (the N still has a lone pair)
• To form tertiary amines, secondary amines are reacted with a haloalkane

Question 11

Give the equations for the formation of propylamine. Give the conditions, and mechanism if applicable.

Answer 11

• Step 1: nucleophilic substitution
• Excess ethanolic ammonia
• 1-chloropropane + ammonia -> propylammonium chloride
• Step 2: check mechanism
• propylammonium chloride + sodium hydroxide -> amine + sodium chloride + water

Question 12

Why is excess ethanolic ammonia used in the formation of primary amines?

Answer 12

• Ethanol is used as a solvent instead of water, as otherwise the haloalkane would react with water via nucleophilic substitution to form an alcohol
• Excess ammonia is used to reduce (although it’s not possible to entirely avoid) further substitution of the amine to form secondary and tertiary amines

Question 13

How are aromatic amines prepared?

Answer 13

• Nitrobenzene is reduced using tin and concentrated hydrochloric acid

Question 14

Give the reaction and conditions for the formation of phenylamine.

Answer 14

• Nitrobenzene + 6[H] -> phenylamine + 2H2O
• Conditions: Sn and concentrated HCl

Question 15

What are amino acids?

Answer 15

• Compounds with an amine group on one end, and a carboxyl group on the other

Question 16

What is the main way that amino acids differ?

Answer 16

• They can be alpha, beta or gamma; this refers to the number of carbon atoms in the central chain between the amine and carboxyl groups
• In α-amino acids, there is only 1 central carbon atom, in β-amino acids, there are 2, and in γ-amino acids, there are 3

Question 17

How are α-amino acids different?

Answer 17

• All of the central carbon atoms have a H group, and an R group
• The R group is what differs between them

Question 18

How do amino acids react with acids?

Answer 18

• The amine group reacts to form an ammonium salt (NH3+X)

Question 19

How do amino acids react with aqueous alkalis?

Answer 19

• The carboxyl group reacts to form a carboxylate salt and water

Question 20

How do amino acids react with alcohols?

Answer 20

• If an amino acid is heated under reflux with an acid catalyst, it forms an ester and water
• The amine group is also protonated due to the acidic conditions

Question 21

What is optical isomerism?

Answer 21

• A type of stereoisomerism

Question 22

What are optical isomers?

Answer 22

• Stereoisomers that are non-superimposable mirror images of each other (think hands)
• (Superimposable: can perfectly overlap if they were in the same place)
• The pair are called enantiomers

Question 23

What causes optical isomerism?

Answer 23

• One or more chiral centres in a molecule

Question 24

What are chiral centres?

Answer 24

• Chiral centres are usually carbon atoms that are bonded to 4 other groups; this makes them asymmetric (if it was bonded to 4 other groups or 2 or more of the same group, you can split the molecule in half and it would look the same)

Question 25

How is the number of chiral centres linked to the number of enantiomers?

Answer 25

• Number of enantiomers: 2^n
• n: number of chiral centres

Question 26

What is condensation polymerisation?

Answer 26

• The joining of monomers with the loss of a small molecule

Question 27

Give 2 examples of types of polymers formed through condensation polymerisation.

Answer 27

• Polyesters
• Polyamides

Question 28

What is required for condensation polymerisation to take place?

Answer 28

• 2 different functional groups

Question 29

What are the 2 ways of making polyesters? What small molecule is made in each reaction, and how much is formed?

Answer 29

• Making them from one monomer that has both a hydroxyl and a carboxyl group
• n-1 water molecules are formed
• Making them from 2 different monomers where one is a dicarboxylic acid and the other is a diol
• 2n-1 water molecules are formed

Question 30

How else can polyesters be formed? What difference is there in the reaction?

Answer 30

• Using acyl and diacyl chlorides instead of carboxylic and dicarboxylic acids
• HCl is formed instead of water

Question 31

What are the 4 ways of making polyamides? What small molecule is made in each reaction, and how much is formed?

Answer 31

• Making them from one monomer that has both an amine and a carboxyl group
• n-1 water molecules are formed
• Making them from one monomer that has both an amine and an acyl chloride group
• n-1 HCl molecules are formed
• Making them from 2 different monomers where one is a dicarboxylic acid and the other is a diamine
• 2n-1 water molecules are formed
• Making them from 2 different monomers where one is a diacyl chloride and the other is a diamine
• 2n-1 HCl molecules are formed

Question 32

What are the 2 main differences between addition and condensation polymerisation?

Answer 32

• Addition polymerisation uses a monomer with a C=C, while condensation polymerisation uses either one monomer with 2 functional groups, or 2 monomers where each has 2 of the same functional group
• In addition polymers, there is a constant carbon chain, while in condensation polymers there are ester and amide linkages

Question 33

In what way do polyesters behave in the same way as esters?

Answer 33

• They can both be hydrolysed by aqueous acid or alkali

Question 34

What does the hydrolysis of polyesters by acid produce?

Answer 34

• Carboxylic acid and alcohol

Question 35

What does the hydrolysis of polyesters by aqueous alkali produce?

Answer 35

• Carboxylate salt and alcohol

Question 36

What does the hydrolysis of polyamides by acid produce?

Answer 36

• Alkylammonium ion and carboxylic acid

Question 37

What does the hydrolysis of polyamides by aqueous alkali produce?

Answer 37

• Carboxylate salt and amine

Question 38

Why are some polyesters biodegradable?

Answer 38

• They can be hydrolysed