Question

Indicate whether the following reaction involves C-O or O-H bond cleavage of the alcohol molecule. C-O bond cleavage O-H bond cleavage Both C-O and O-H bond cleavage.

Answer 1

Concepts and reason

Proton abstraction: In many of organic compounds, protons are abstracted by using a strong base like ${\rm{NaN}}{{\rm{H}}_{\rm{2}}}{\rm{,}}\,{\rm{NaOH,}}$ etc.

Nucleophilic substitution: Nucleophile is an electron-rich species, which attack on the electron poor part by replacing a leaving group of the organic compound; this process is known as nucleophile substitution process.

Fundamentals

Proton abstraction by a base is shown below.

Nucleophile substitution reactions are of two types;

1. ${{\rm{S}}_{\rm{N}}}{\rm{1}}$ reaction

Reaction rate depends only on the concentration of the substrate

2. ${{\rm{S}}_{\rm{N}}}{\rm{2}}$ reaction

Reaction rate depends on both substrates as well as reagents.

Given transformation is drawn below.

It is clear that the first step in the reaction is abstraction of proton by a base and the second step is a nucleophilic substitution reaction.

Given transformation is drawn below.

Mechanism of the reaction is drawn below.

Clear from the above mechanism that ${\rm{ - O - H}}$ bond breaks to give oxide ion as nucleophile in the reaction.

Ans: