Question

Arrange the following nucleophiles in the decreasing order of nucleophilicity:
A.

B. $CH_{3}O^{-}$
C. $CN^{-}$
D.

I. C, B, A, D
II. A, B, C, D
III. D, C, B, A
IV. D, A, C, B

Answer 1

The nucleophilicity of different nucleophiles depends on many things. And one amongst them is increasing base strength indicates decreasing nucleophilic strength.

Complete step-by-step answer: - Nucleophilicity of the nucleophile strength is referring to a substance’s nucleophilic character and is often used to compare the affinity of atoms.
- It describes the affinity of a nucleophile to the positively charged atomic nuclei of atoms.
- We know that nucleophiles are electron rich species in search of nucleus or positive center (Nucleus – nucleus, phile – loving). Therefore, these can be either negatively charged or even neutral.
- Now, in order to solve the question, we need to consider the conjugate bases of the given options and then obtain the order of acidic nature.
- The conjugate bases are shown below:

$CH_{3}O^{-}\rightarrow CH_{3}OH$
$CN^{-}\rightarrow HCN$
$p-H_{3}C-C_{6}H_{4}-\ SO_{2}-O^{-}\rightarrow p-H_{3}C-C_{6}H_{4}-SO_{2}-OH$
- The order of acidic nature is D > A > C > B
- So, the increasing order of nucleophilicity will be B > C > A > D

Therefore, the correct answer is (D).

Note: The important thing to keep in mind is that the order of nucleophilicity is the reverse: the order of basicity and nucleophilicity increases down the group in the periodic table. Lesser the electronegativity of donor atoms more is its tendency to give a lone pair of electrons, and thus more is its nucleophilic strength.