The correct answer is option 4. 2,2-Dimethylpropanal.
The least reactive aldehyde towards \(HCN\) would be 2,2-Dimethylpropanal. Here's why:
The reactivity of aldehydes towards nucleophilic addition reactions, like the reaction with HCN, depends on two main factors:
- Steric hindrance: Bulky groups around the carbonyl carbon \((C=O)\) hinder the approach of the nucleophile, making the reaction slower.
- Electronic effect: Electron-donating groups near the carbonyl carbon increase the negative charge density on the oxygen, making it more attractive to the electrophilic carbon of \(HCN\), leading to a faster reaction.
In the given options:
- Methanal \((HCHO)\): It has no steric hindrance and the hydrogen group has a slight electron-withdrawing effect, making it relatively reactive.
- Ethanal \((CH_3CHO)\): The methyl group introduces some steric hindrance, but it's still less hindered than the options with two bulky groups.
- Propanal \((CH_3CH_2CHO)\): Similar to Ethanal, the propyl group creates some steric hindrance, but less than the most hindered option.
- 2,2-Dimethylpropanal \((CH_3)_3C-CHO\): This molecule has two bulky methyl groups directly attached to the carbon next to the carbonyl carbon, creating significant steric hindrance that interferes with the approach of \(HCN\). This steric effect outweighs any electronic effect from the methyl groups, making it the least reactive option.
Therefore, due to the significant steric hindrance from its two bulky methyl groups, 2,2-Dimethylpropanal is the least reactive aldehyde towards \(HCN\) among the given options. |
