Question

Which of the following compounds is most reactive towards nucleophilic addition reaction?

• A. $\mathrm{PhCOPh}$
• B. ${\mathrm{CH}}_3\mathrm{CHO}$
• C. ${\mathrm{PhCOCPh}}_3$
• D. ${\mathrm{CH}}_3{\mathrm{COCH}}_3$

Answer 1

The correct option is B

${\mathrm{CH}}_3\mathrm{CHO}$

Explanation for the correct option:

B. ${\mathrm{CH}}_3\mathrm{CHO}$

Nucleophilic addition reaction:

• Carbonyl carbon undergoes nucleophilic addition reactions.
• Nucleophilic addition reaction occurs if the substituent on carbonyl carbon stabilizes the positive charge on carbonyl carbon by withdrawing electrons.
• If an atom attached with carbonyl carbon shows -I effect, then it decreases electron density or carbonyl carbon.
• The phenyl $\left(\mathrm{Ph}\right)$ ring gives +R effect, hence decreasing the reactivity for nucleophilic addition.
• In ${\mathrm{CH}}_3\mathrm{CHO}$, the positive charge is stabilized by the presence of $\mathrm{H}$ in ${\mathrm{CH}}_3\mathrm{CHO}$.

Explanation for incorrect options:

A. $\mathrm{PhCOPh}$

• The presence of two phenyl groups $\left(\mathrm{Ph}\right)$ decreases the reactivity of carbonyl carbon $(\mathrm{C}=\mathrm{O})$.

C. ${\mathrm{PhCOCPh}}_3$

• The presence of phenyl group $\left(\mathrm{Ph}\right)$ decreases the reactivity of carbonyl carbon $(\mathrm{C}=\mathrm{O})$.

D. ${\mathrm{CH}}_3{\mathrm{COCH}}_3$

• The presence of 1 methyl group $(-{\mathrm{CH}}_3)$ decreases the reactivity of carbonyl carbon $(\mathrm{C}=\mathrm{O})$ in comparison to ${\mathrm{CH}}_3\mathrm{CHO}$.

Hence, the correct option is (B) i.e. ${\mathrm{CH}}_3\mathrm{CHO}$.