Question

Choose the correct answer among the alternatives given :
Consider the following $S_{N}2$ reactions
I. $RX+Y^{-}\to R-Y+X^{-}$
II. $RX+Y\to R-Y^{+}+X^{-}$
III. $R{X}^{+}+Y^{-}\to RY+X$
IV. $R{X}^{+}+Y\to R{Y}^{+}+X$
In which reactions there is large increase and large decrease in rate of reaction respectively with increase in polarity of the solvent.

• A. II and III
• B. II and IV
• C. I and IV
• D. IV and I

Answer 1

The correct option is A II and III

The highest increase in the rate of the reaction can be seen in case (II) because the transition state of SN2 reaction is more stable.
In (III) case, even though increase in polarity of solvent will lead to reduce the rate of the reaction due to the opposite polarity of the solvent.
Hence, option A is correct.