Question

In order of preference while selecting the principal functional group which compounds are preferable to ketones: (This question has multiple correct options)
A. alcohols
B. anhydrides
C. aldehydes
D. alkenes

Answer 1

Hint: Carboxylic acids and their derivatives have highest priority. The general form of Carboxylic acid is $R - \mathop {\mathop C\limits_{||} }\limits_O - OH$. hen The carbonyl group and its derivatives have the highest priority. Ketone ($R - \mathop {\mathop C\limits^| }\limits^R = O$) is a carbonyl derivative. So find the carboxyl groups and carbonyl groups present in the given options and those will be the required answers.

Complete step by step solution:
We are given to find the compounds with principal functional groups which have higher priority than ketones.
First one is alcohol. Alcohols are compounds containing hydroxyl groups ($ - OH$) as a functional group. It is not a derivative of a carboxylic acid or a carbonyl group.
Second one is anhydrides. Anhydrides are derivatives of carboxylic acids. In anhydrides, two acyl groups are joined by only one oxygen atom. General form of an anhydride is $R - \mathop {\mathop C\limits_{||} }\limits_O - O - \mathop {\mathop C\limits_{||} }\limits_O - R$. It is a carboxylic acid derivative.
Third one is aldehydes. Aldehydes are carbonyl derivatives. The general form of an aldehyde is $R - \mathop {\mathop C\limits^| }\limits^H = O$.
Fourth one is Alkenes. Alkene compounds have carbon-carbon double bonds (C=C). These are not a derivative of a carboxylic acid or a carbonyl group.
Therefore as we can see, anhydride is a carboxylic acid derivative and has the highest priority.
Aldehydes and ketones are carbonyl derivatives. Aldehydes have a higher priority than ketones. Because of the presence of two alkyl groups in a ketone, its priority decreases.
The priority order is Anhydride>Aldehyde>Ketone>Alcohols>Alkenes.
Anhydrides and aldehydes have higher priority than ketones.

Therefore, Option B and Option C are correct.

Note:
Do not confuse between an aldehyde and a ketone. Aldehyde and ketone both incorporate a carbonyl functional group ($C = O$). Aldehyde is a type of ketone where one R-group of ketone is replaced with a hydrogen atom. Presence of a hydrogen atom attached to carbon-oxygen double bond is seen in aldehyde whereas it is not seen in a ketone.