3.8 Aldehydes and Ketones

Question 1

What shape is the carbonyl group in aldehydes and ketones?

Answer 1

It is planar

Question 2

What is the mechanism for the reduction of aldehydes and ketones?

Answer 2

Nucleophilic addition

Question 3

What is a source of hydride and hydrogen ions?

Answer 3

Sodium borohydride

NaBH4

Question 4

Describe the reduction of propanone through nucleophilic addition to form propan-2-ol.

Answer 4

1) An arrow is drawn from the lone pair on a hydride ion is to the delta+ on a carbon in the carbonyl group. An arrow is drawn from the double C=O bond to the O
2) A negative intermediate is formed with the hydrogen now bonded to the carbon and the O having a lone pair and negative charge. An arrow is drawn from this lone pair to the hydrogen ion.
3) Propan-2-ol is formed.

Question 5

What is the proportion on enantiomers formed from nucleophilic addition and why?

Answer 5

A racemic mixture is formed, as the carbonyl group can be attacked from either behind or in front, meaning that naturally a 50-50 split is made. This means that 50% are +enantiomers and 50% are -enantiomers