Question

The correct sequence of decreasing order of reactivity of hydrolysis of acid chlorides is
A. $PhCOCl > p - {O_2}N{C_{_6}}{H_5}COCl > p - C{H_3}{C_6}{H_5}COCl$
B. $PhCOCl > p - C{H_3}{C_6}{H_5}COCl > p - {O_2}N{C_6}{H_5}COC{l^{}}$
C. $p - {O_2}N{C_6}{H_5}COCl > PhCOCl > p - C{H_3}{C_6}{H_5}COCl$
D. $p - {O_2}N{C_6}{H_5}COCl > p - C{H_3}{C_6}{H_5}COCl > PhCOCl$

Answer 1

Hint: Hydrolysis of acid chloride defined as nucleophilic attack of lone pairs of oxygen present in water, on carbon atoms to form carboxylic acid. Greater positive charge on a carbon atom attached to a functional group, greater its reactivity towards hydrolysis.

Complete step by step answer:
Acid chlorides also known as acyl chlorides, are formed when the $ - COCl$ group is attached to an organic compound. They are commonly written as $ROCl$ .
Now, it undergoes nucleophilic substitution reaction when reacted with hydroxyl group, and tends to result in formation of carboxylic group. It is known as hydrolysis of acid chloride.
Reactivity of acid chloride to undergo hydrolysis depends on the carbon atom attached to the carbonyl group, greater positive charge on carbon greater its reactivity towards hydrolysis.
Now, in question we have three variants of acid chloride;
1. $PhCOCl - $ Benzoyl chloride
2. $p - {O_2}N{C_6}{H_5}COCl$- para-nitro benzoyl chloride
3. $p - C{H_3}{C_6}{H_5}COCl$ - para-methyl benzoyl chloride
Now, the second and third option has different function groups attached to it as substitutes, considering the effect of this functional group on carbon atoms we can conclude the reactivity series.
Both $N{O_2}$ and $C{H_3}$ tend to show mesomeric effect, it can be understood as tendency of electron withdrawing and electron releasing of substitutes due to resonance., denoted by $M$.
4. $PhCOCl - $ there is no extra functional group attached, so it does not show $M$.
5. $p - {O_2}N{C_6}{H_5}COCl$-. there is an electron withdrawing$N{O_2}$ attached at para position, showing $ - M$,increasing positive charge on carbon.
6. $p - C{H_3}{C_6}{H_5}COCl$- there is an electron releasing $C{H_3}$ attached at para position, showing $ + M$,decreasing positive charge on carbon.
So the order of reactivity is;
$p - {O_2}N{C_6}{H_5}COCl > PhCOCl > p - C{H_3}{C_6}{H_5}COCl$
Hence, the correct answer is, ‘C. $p - {O_2}N{C_6}{H_5}COCl > PhCOCl > p - C{H_3}{C_6}{H_5}COCl$’.

Note: In such questions always remember to find how removal of addition of a group affects the reactivity of compounds. Once it's found, the order of the reactivity or series becomes easy to determine.