Alcohols and Haloalkanes

Question 1

What happens when you oxidise primary, secondary and tertiary alcohols in different conditions

Answer 1

Primary alcohols: Distillation-Aldehydes, Reflux-Carboxylic acid
Secondary alcohols:
Reflux-Ketone
Tertiary alcohols:
Have no hydrogens so resist oxidation

Question 2

Elimination reaction of alcohol

Answer 2

Eliminates water and requires H3PO4 and heat to form alkenes

Question 3

Substitution with halide ions in presence of acid

Answer 3

NaBr + H2SO4 –> NaHSO4 + HBr

The hydrogen halide is required to react with the alcohol producing water and a haloalkane

Question 4

Esterification

Answer 4

Alcohol and carboxylic acid, together with H2SO4 which acts as a dehydrating agent, moving the equilibrium to the right

Question 5

Name three uses of CFCs

Answer 5

Refrigerators, AC units and aerosol propellants

Question 6

Hydrolysis of haloalkanes in aqueous alkali

Answer 6

Nucleophilic substitution. OH- attacks from opposite side to halogen because of polarity, so repulsion is reduced.

Question 7

Sn2 mechanism

Answer 7

One step mechanism, where nucleophile attacks as the halide leaves. It happens fastest with primary halides because the trigonal bipyramidal transition state is less sterically hindered. The rate of this reaction depends on both haloalkane and nucleophile.

Question 8

Sn1 mechanism

Answer 8

Two step mechanism where halide leaves first, then nucleophile attacks. It happens fastest with tertiary haloalkanes as the planar carbocation intermediate is stabilised by the alkyl groups. In this way the rate of reaction depends only on the haloalkane.

Question 9

Explain the trend in hydrolysis of primary haloalkanes

Answer 9

The further down the group you go, the faster the reaction. This is because the further down you go, the lower the bond enthalpy, so it is more easy to break.