Question

31. Rank the following compounds in order of increasing rates of their SN2 reactions.

Rank the following compounds in order of increasing rates of their Sn2 reactions

Answer 1

Concepts and reason

The mentioned problem is based on the concept of ${{\rm{S}}_{\rm{N}}}{\rm{2}}$ substitution reaction which is a biomolecular nucleophilic substitution. This reaction does not involve the formation of intermediates. Nucleophiles are the chemical species which have high electron density. Presence of lone pair of electrons and negative charge indicates the high electron density of that compound.

Fundamentals

Nucleophilic substitution reaction involves the replacement of a weak nucleophile by a strong nucleophile. Carbon which is attached to the weak nucleophile is electrophilic. Thus, a strong nucleophile attacks at this carbon and replaces the weak nucleophile. The rate of ${{\rm{S}}_{\rm{N}}}{\rm{2}}$ reactions depends on both reagent and reactant.

The compounds are secondary, primary and secondary as follows:

The order of reaction rate based on ${{\rm{S}}_{\rm{N}}}{\rm{2}}$ mechanism will be as follows:

${\rm{Primary}} > {\rm{Secondary}} > {\rm{Vinylic}}$

The vinylic halide is not at all stabilized in fact it is very unstable in nature so it does not want to go under ${{\rm{S}}_{\rm{N}}}2$ reaction.

Ans: