Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions.

(i) Ethanal, Propanal, Propanone, Butanone.

(ii) Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Acetophenone. 

<p><strong> (i)</strong> <strong>Ethanal, Propanal, Propanone, Butanone</strong></p><p>The +I effect increases in the order as:</p><p>Ethanal&lt;propanal&lt;propanone&lt;butanone.&lt; p=""&gt; &lt;/propanal&lt;propanone&lt;butanone.&lt;&gt;</p><p>Therefore, the electron density of the carbonyl carbon increases as the +I effect due to the alkyl group increases. As a result, the chances of attack by a nucleophile (which are rich in electrons and carry a negative charge, not necessarily usually have a lone pair of an electrons) decrease because the carbonyl carbon has electron density on it. Hence, the increasing order of the reactivity of the given compounds in nucleophilic addition reaction is:</p><p>Ethanal &gt; Propanal&gt; Propanone &gt; Butanone.</p><p><strong> (ii)</strong> <strong>Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Acetophenone:</strong></p><p>The +I effect is more in ketone than in aldehyde because in ketone, there are 2 alkyl groups contributing in the +I effect whereas in aldehydes, there is only one alkyl group. Hence, acetophenone (being a ketone group attached to it) is the least reactive in nucleophilic addition reactions.</p><p>Among aldehydes, the +I effect is the highest in <em>p-</em>tolualdehyde because of the presence of the electron- donating –CH₃ group (which increase the electron density on the carbonyl carbon via resonance through the benzene ring) and the lowest in <em>p</em>-nitrobenzaldehyde because of the presence of the electron- withdrawing –NO₂ group (which decreases the electron density on the carbonyl carbon via resonance through the benzene ring). Hence, the increasing order of the reactivity of the given compounds is:</p><p>Acetophenone&lt;<em>p</em>-tolualdehyde&lt;benzaldehyde&lt;<em>p-Nitrobenzaldehyde&lt;/benzaldehyde&lt;</em></p>

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