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.
Hint: Consider steric effect and electronic effect.

Explanation

( i) As we more from ethanal to propanone to butanone the +I inductive effect of alkyl group increases as a result the + ve charge on the carbon atom of the carbonyl group progressively decreases and hence attack by
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Thus the reactivity increases in the order :
Butanone < propanone < propanol < ethanal
(ii ) Among these compounds acetophenone is a ketons while all others are aldehydes acetophenone is least reactive In P- tolualdehyde there is a methyl `(CH_3)` group at the para postion w.r.t the carbonyl group which increases electron density or decreases +ve charge on the carbon on the carbon of the carbonyl group by hyperconjugation effect making

On the other hand . in p - nitrobenzaldehyde the `-NO_2` is an electron withdrawing group .It withdraws electrons , both by inductive and reasonance effect thereby decreasing electron density ( or increasing +Ve charge ) on the carbon atom of the carbonyl group .this facilitates the attack of the nucleophile and hence makes it more reactive than benzaldehyde .

THerefore , teh correct order of reactivity is
` Acetophenone < P- tolualdehyde < benzaldehyde < p - nitrobenzaldehyde.