Identify the correct decreasing order of reactivity for the following compounds towards an S _ N 2 substitution reaction: (I) (II) (III)

Step-by-step solution

The reactivity of a compound towards an S _ N 2 reaction depends on the steric hindrance around the electrophilic carbon and the electronic stabilization of the transition state. 1. Compound (I) - Vinyl chloride: The chlorine atom is attached to an sp^2 hybridized carbon. The lone pairs on the chlorine atom are in conjugation with the bond, giving the C - Cl bond partial double bond character. This makes the bond difficult to break. Furthermore, sp^2 carbons are highly unreactive towards S _ N 2 reactions due to el