Question

Which of the following is a nucleophilic addition reaction?
This question has multiple correct options
$C{H_3}COCl\,\,\xrightarrow{{C{H_3}MgBr\,\,(1eq.)}}\,\,C{H_3}COC{H_3}$
$C{H_3}COC{H_3}\,\xrightarrow{{{I_2}/O{H^ - }/\Delta }}\,\,C{H_3}CO{O^ - }\,\, + \,\,CH{I_3}$
$PhCHO\,\,\xrightarrow{{KCN/{H^ + }}}\,\,PhCH(OH)(CN)$
$C{H_3}C \equiv CMgBr\,\,\xrightarrow{{C{H_3}Br}}\,\,C{H_3}C \equiv CC{H_3}$

Answer 1

To solve this question, we must first understand the basic concepts about nucleophilic addition reaction. Then we need to assess the important points of the concept and check all the provided options that follow the mechanism of nucleophilic addition reaction or not and then only we can conclude the correct answer(s)..

Complete solution:
Before we move forward with the solution of this given question, let us first understand some basic concepts:
Nucleophilic Addition Reaction: is a chemical addition reaction in which a nucleophile forms a sigma bond with an electron deficient species. These reactions are considered very important in organic chemistry since they enable the conversion of carbonyl groups into a variety of functional groups. Generally, nucleophilic addition reactions of carbonyl compounds can be broken down into the following three steps:
The electrophilic carbonyl carbon forms a sigma bond with the nucleophile.
The carbon-oxygen pi bond is now broken, forming an alkoxide intermediate (the bond pair of electrons are transferred to the oxygen atom).
The subsequent protonation of the alkoxide yields the alcohol derivative.
Step 1: We will consider each option one by one:
The first option is: $C{H_3}COCl\,\,\xrightarrow{{C{H_3}MgBr\,\,(1eq.)}}\,\,C{H_3}COC{H_3}$
In this option clearly, Grignard reagent $C{H_3}MgBr$ which acts as nucleophile and adds across $- C = O$ bond hence it is a Nucleophilic Addition Reaction.
The second option is: $C{H_3}COC{H_3}\,\xrightarrow{{{I_2}/O{H^ - }/\Delta }}\,\,C{H_3}CO{O^ - }\,\, + \,\,CH{I_3}$
In this option clearly, we can see that the reagent is not adding any nucleophile to the reactant. And therefore it is not a Nucleophilic Addition Reaction.
The third option is: $PhCHO\,\,\xrightarrow{{KCN/{H^ + }}}\,\,PhCH(OH)(CN)$
Here in the reaction, $KCN$ adds to the carbonyl group of benzaldehyde. Cyanide ions act as nucleophiles. This is followed by acid hydrolysis to form cyanohydrin.
Hence, the reaction is a nucleophilic addition reaction.
The last option is: $C{H_3}C \equiv CMgBr\,\,\xrightarrow{{C{H_3}Br}}\,\,C{H_3}C \equiv CC{H_3}$
Here in the reaction, clearly we can see that the species which is being added to the reagent is not a nucleophile, it’s an electrophile. And therefore it is not a Nucleophilic Addition Reaction.
So, clearly we can conclude that the correct answers are _Option A and C._

Note: Aldehydes are more reactive and readily undergo nucleophilic addition reactions in comparison to ketones. Aldehydes demonstrate more favourable equilibrium constants for addition reactions than ketones because of electronic and steric effect. In the case of ketones, two large substituents are present in the structure of ketones which causes steric hindrance when the nucleophile approaches the carbonyl carbon.