Q.Aldehydes are more reactive toward nucleophilic addition reactions than ketones. Explain.

Step 1. Electronic effect (section 12.7.1, point 1). Alkyl groups have an electron-DONATING inductive effect (+I). A ketone's carbonyl carbon carries TWO such alkyl groups, so their combined +I donation more strongly reduces the carbonyl carbon's positive polarity (and hence its electrophilicity). An aldehyde's carbonyl carbon carries only ONE alkyl group (plus a hydrogen, which has no comparable +I effect), so it retains MORE electrophilicity, and is correspondingly more attractive to an incoming nucleophile.

Step 2. Steric effect (section 12.7.1, point 2). A ketone's two bulky alkyl groups physically crowd the space around the carbonyl carbon, hindering a nucleophile trying to approach it -- 'steric hindrance to nucleophilic attack'. An aldehyde, with just one alkyl group and one small hydrogen atom on its carbonyl carbon, is much less crowded, so a nucleophile can approach and attack it more easily. …

Recalling and explaining both combined factors given in section 12.7.1 -- the electronic (+I inductive) effect and the steric-hindrance effect -- that tog …

• Giving only ONE of the two reasons (electronic OR steric) when the section explicitly identifies both as jointly responsible.
• Reversing the electronic argument and claiming the alkyl groups' +I effect INCREASES electrophilicity, when in fact electron-DONAT …