The order of reactivity of the given haloalkanes towards...

The order of reactivity of the given haloalkanes towards nucleophile is :
(a) $\mathrm{RI}>\mathrm{RBr}>\mathrm{KCl}$
(b) $\mathrm{RCl}>\mathrm{RBr}>\mathrm{RI}$
(c) $\mathrm{RBr}>\mathrm{RCl}>\mathrm{RI}$
(d) $\mathrm{RBr}>\mathrm{RI}>\mathrm{RCl}$

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Key Concepts

Halogen Reactivity Trends

The order of reactivity for haloalkanes in nucleophilic substitution reactions typically mirrors the ability of the attached halogen to act as a leaving group. Due to its larger size and better polarizability, iodide is a superior leaving group compared to bromide and chloride, resulting in a higher reactivity for iodide-containing haloalkanes compared to those with bromide or chloride.

Leaving Group Ability

In nucleophilic substitution reactions, the reactivity of a haloalkane is largely determined by the quality of the leaving group. A better leaving group can stabilize the negative charge it acquires after departure, thus facilitating the reaction. Generally, leaving groups that are more polarizable and less basic, such as iodide, are superior to those that are smaller and more basic, such as chloride.

SN2 Reaction Mechanism

The SN2 mechanism is a single-step nucleophilic substitution process where the rate of reaction depends on both the nucleophile and the substrate. In this concerted mechanism, the nucleophile attacks the carbon atom simultaneously as the leaving group begins to depart, which is influenced by the leaving group’s ability to stabilize the negative charge and by steric hindrance at the reaction site.

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