Aldehydes and Ketones
Carbonyl compounds have a C=O bond. They do not hydrogen bond instead having permanent
dipole forces. The C=O bond is polarised because O is more electronegative than C. The
positive carbon atom attracts nucleophiles. C=O is stronger than C=C therefore addition
reactions occur less easily. Smaller carbonyl compounds are more soluble in water as they can
form hydrogen bonds.
Oxidation of Aldehydes --> Carboxylic Acid
Aldehydes can be oxidised due to their H bonded to the carbon with the carbonyl group.
Ketones do not have this.
Potassium dichromate (vi) and sulphuric acid - heated under reflux. Colour change orange -->
green.
To stop the oxidation of an aldehyde past when it is needed:
Distillation should occur removing the aldehyde when it is produced preventing it being
oxidised further.
Use an excess of the alcohol so there is not enough oxidising agent for the stages to
proceed further.
Reducing Aldehydes and Ketones
Reducing agents such as NaBH4 (sodium tetrahydraborate) and LiAlH4 (lithium
tetrahydraluminate) reduce carbonyls to alcohols.
Aldehydes are reduced to primary alcohols and ketones to secondary alcohols.
Carbonyl compounds have a C=O bond. They do not hydrogen bond instead having permanent
dipole forces. The C=O bond is polarised because O is more electronegative than C. The
positive carbon atom attracts nucleophiles. C=O is stronger than C=C therefore addition
reactions occur less easily. Smaller carbonyl compounds are more soluble in water as they can
form hydrogen bonds.
Oxidation of Aldehydes --> Carboxylic Acid
Aldehydes can be oxidised due to their H bonded to the carbon with the carbonyl group.
Ketones do not have this.
Potassium dichromate (vi) and sulphuric acid - heated under reflux. Colour change orange -->
green.
To stop the oxidation of an aldehyde past when it is needed:
Distillation should occur removing the aldehyde when it is produced preventing it being
oxidised further.
Use an excess of the alcohol so there is not enough oxidising agent for the stages to
proceed further.
Reducing Aldehydes and Ketones
Reducing agents such as NaBH4 (sodium tetrahydraborate) and LiAlH4 (lithium
tetrahydraluminate) reduce carbonyls to alcohols.
Aldehydes are reduced to primary alcohols and ketones to secondary alcohols.
