question_answer

Arrange the compounds \[C{{H}_{3}}F,\,\,C{{H}_{3}}I,\,\,C{{H}_{3}}Br,\,C{{H}_{3}}Cl\] in order of increasing reactivity in bimolecular nucleophilic substitution \[({{S}_{N}}^{2})\] reactions.

Answer:

                \[C{{H}_{3}}F<C{{H}_{3}}Cl<C{{H}_{3}}Br<C{{H}_{3}}I\] In these nucleophilic substitution reactions, the nucleophile is to displace the halide ion \[({{X}^{-}})\]. Greater the bond dissociation enthalpy of the C-X bond, difficult is its cleavage and lesser will be the reactivity. The order of bond dissociation enthalpy of different C-X bonds is: \[C-F>C-Cl>C-Br>C-I\] The order of reactivity towards \[{{S}_{{{N}^{2}}}}\] reactions is the reverse.