Question

Arrange the following in the correct order of their nucleophilicity:
I) \[C{H_3} - O - C{H_2} - {O^ - }\]
II) \[Ph - C{H_2} - {O^ - }\]
III) \[C{H_3} - {O^ - }\]
IV) \[C{H_3} - C{H_2} - {O^ - }\]
A.IV > III > II > I
B.I > II > III > IV
C.II > IV > III > I
D.II > I > IV > III

Answer 1

Hint: Nucleophilicity is the ability of a nucleophile to displace a leaving group in a substitution reaction. The electron withdrawing groups (EWG) decrease the nucleophilicity of an atom while the electron donating groups (EDG) increase the nucleophilicity of an atom.

Complete step by step answer: A nucleophile is a chemical species that can donate an electron pair to form a chemical bond in relation to a reaction. All molecules or ions with a free pair of electrons or at least one pi bond can act as nucleophiles.
In the given question, we will need to investigate each molecule individually.
* \[C{H_3} - O - C{H_2} - {O^ - }\] (I)
In this compound, there is no conjugation for the electrons of -O- group through which the electron density on the negatively charged oxygen can increase. However, the -I (EWG) effect of the neutral oxygen decreases the nucleophilicity of the negatively charged oxygen.

* \[Ph - C{H_2} - {O^ - }\] (II)
In this compound, there is no conjugation for the pi electrons of the benzene ring through which the electron density on the negatively charged oxygen can increase. However, the -I (EWG) effect of the \[s{p^2}\] carbons decreases the nucleophilicity of the negatively charged oxygen. The -I effect of oxygen is greater than the -I effect of \[s{p^2}\] carbons.

* \[C{H_3} - {O^ - }\] (III)
The +I (EDG) effect of methyl group increases the nucleophilicity of the negatively charged oxygen.

* \[C{H_3} - C{H_2} - {O^ - }\] (IV)
The +I (EDG) effect of ethyl methyl group increases the nucleophilicity of the negatively charged oxygen. The +I effect of ethyl group is greater than the +I effect of methyl group.

Hence, the correct answer is (A) IV > III > II > I

Note: Remember that the -I effect decreases the electron donating tendency of the nucleophile as it attracts the electrons towards itself. Thus, the tendency to donate to outer electrophiles decreases and vice – versa for +I effect.