Question

Explain the nature of carbonyl group and carboxylic group.

Hint:

Carbonyl groups are mainly reactive towards nucleophiles (nucleophilic addition), while carboxylic groups show acidic character and hydrogen bonding due to –COOH functionality.

Answer 1

Carbonyl group (C=O):
- The carbonyl group consists of a carbon atom double-bonded to an oxygen atom.
- The C=O bond is polar because oxygen is more electronegative than carbon.
- The carbon atom has a partial positive charge ($\delta^+$) and oxygen a partial negative charge ($\delta^-$).
- This polarity makes the carbonyl carbon susceptible to nucleophilic attack and the oxygen capable of hydrogen bonding.
- Hence, aldehydes and ketones (which contain the carbonyl group) undergo nucleophilic addition reactions.
Carboxylic group (–COOH):
- The carboxyl group is composed of a carbonyl group (C=O) and a hydroxyl group (–OH) attached to the same carbon.
- Due to resonance, the carboxyl group exists as a hybrid of two structures, making the C–O bonds equivalent.
- The O–H bond is highly polar, so carboxylic acids are acidic in nature and readily donate a proton (H$^+$).
- They form dimers through strong intermolecular hydrogen bonding, giving them higher boiling points.