Which functional group is present in Butanoic acid?

Question

Accepted Answer

The correct option is (4):

Butanoic acid is an organic compound that belongs to the class of carboxylic acids. The name "butanoic acid" itself provides a strong clue to its functional group. The suffix "-oic acid" is characteristic of carboxylic acids. A carboxylic acid functional group is represented by $\mathrm{-COOH}$, which consists of a carbonyl group ($\mathrm{C=O}$) directly bonded to a hydroxyl group ($\mathrm{-OH}$). The general formula for a carboxylic acid can be written as $\mathrm{R-COOH}$, where R represents an alkyl or aryl group. In the case of butanoic acid, 'but-' indicates a four-carbon chain, and the '-oic acid' indicates the presence of the carboxylic acid group. Therefore, the structure of butanoic acid is $\mathrm{CH_3CH_2CH_2COOH}$. This functional group is responsible for the acidic properties of these compounds, as the hydrogen atom of the hydroxyl group can be donated as a proton ($\mathrm{H^+}$).

The incorrect option is (1): Aldehyde.
Aldehydes contain a carbonyl group ($\mathrm{C=O}$) bonded to at least one hydrogen atom and typically an alkyl or aryl group ($\mathrm{R-CHO}$). While they contain a carbonyl group, they lack the hydroxyl group that defines carboxylic acids.

The incorrect option is (2): Ketone.
Ketones contain a carbonyl group ($\mathrm{C=O}$) bonded to two alkyl or aryl groups ($\mathrm{R-CO-R'}$). Like aldehydes, they have a carbonyl group but do not have a hydroxyl group directly attached to the carbonyl carbon, differentiating them from carboxylic acids.

The incorrect option is (3): Alcohol.
Alcohols are characterized by the presence of a hydroxyl group ($\mathrm{-OH}$) attached to a saturated carbon atom ($\mathrm{R-OH}$). While the carboxylic acid group contains a hydroxyl group, it is specifically attached to a carbonyl carbon, which is not the definition of an alcohol functional group.