Chapter 28 - Amines

Question 1

Describe the shape of amines

Answer 1

• Ammonia is a pyramidal molecule with a bond angle of 107

Question 2

Describe the boiling point of amines

Answer 2

• Hydrogen bond using -NH2 group
• But as N is less electronegative than O, hydrogen bonds are not as strong as in alcohols

Question 3

Describe the smell of amines

Answer 3

Fishy

Question 4

Describe the solubility of amines

Answer 4

• Up to 4C are soluble in water and alcohol due to hydrogen bonding
• Most amines are also soluble in less polar solvents

Question 5

Define aliphatic amines

Answer 5

Amines with alkyl groups attached to the N

Question 6

Define aromatic amines

Answer 6

Amines with the N joined directly to a benzene ring

Question 7

Describe the basic nature of amines

Answer 7

• Bronsted-Lowry bases
• Lone pair on the N atom can readily accept a proton

Question 8

List the base strength of amines

Answer 8

Aliphatic amines > NH3 > aromatic amines

Question 9

Describe why aliphatic amines are so basic

Answer 9

• Alkyl groups push electrons towards the N (a positive inductive effect)
• Increases the availability of the N lone pair
• Increases ability to accept H+

Question 10

Describe why aromatic amines are not so basic

Answer 10

• The N lone pair is partially delocalised into the benzene ring
• Reduces availability of the N lone pair
• Reduces ability to accept H+

Question 11

Describe the uses of amines

Answer 11

• Manufacture of synthetic materials
• Quaternary ammonium compounds are used to make hair and fabric conditioner

Question 12

Describe why quaternary ammonium compounds make good fabric and hair conditioners

Answer 12

• They form positive cations
• Attracted to the negative charges on wet fabric and hair
• Form a coating that prevents the build-up of static electricity