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Arrange the following compounds in an increasing order or their reactivity in nucleophilic addition reactions: ethanal, propanal, propanone, butanone.

Arrange the following compounds in an increasing order or their reactivity in nucleophilic addition reactions: ethanal, propanal, propanone, butanone.

Grade:12

1 Answers

Aarti Gupta
askIITians Faculty 300 Points
9 years ago
The increasing order of reactivity towards nucleophilic addition reactions between the above mentioned carbonyl compounds will be-
Butanone<propanone<propanal<ethanal
The reason of above mentioned order can be explained as-- For maximum reactivity towards nucleophiles, the carbonyl carbon atom should be positive and also not sterically hindered by adjacent groups.Now in case of ketones there are two alkyl groups on carbonyl carbon while aldehydes have one alkyl group only. Each alkyl group being electron-releasing(+I effect) will decreases the positivity of carbon atom and on account of its bulk offers steric hindrance to approaching reagents. For both these reasons, the nucleophilic attack on the carbonyl carbon retarded. Thus the carbonyl group in ketones being influenced by two alkyl groups is less reactive than in aldehydes where the carbonyl group is under the influence of one alkyl group only.And as the number of alkyl groups increases both the +I effect and the stearic hinderance get increased preventing the attack of nucleophile.So ethanal will show highest reactivity towards the nucleophilic addition reactions because of minimum no. of alkyl group.

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