Fundamentals of Organic ChemistryChemistryHaloalkanes and Haloarenes
Identify the S _ N 2 reaction that is favoured (i.e., its rate increases) in a polar protic medium.
Options
- ANH ₃ + Me - I H ₂ N - Me + H - I
- BNaOH + CH ₃- I HO - CH ₃ + NaI
Correct answer
A. NH ₃ + Me - I H ₂ N - Me + H - I
Step-by-step solution
The effect of a solvent on the rate of an S_N2 reaction depends on how it stabilizes the reactants compared to the transition state (Hughes-Ingold rules). In option (A), both reactants ( NH ₃ and Me-I ) are neutral. During the formation of the transition state, a partial positive charge develops on the nitrogen atom and a partial negative charge develops on the leaving iodine atom ( [ H ₃ N ^ + Me I ^ - ]^ ). A polar protic solvent stabilizes this charge-separated transition state much more than the neutral reactan