Question

Pick out the following factor(s) which promote a $S_{N}1$ reaction :
I. Low temperature
II. Concentraton of nucleophile
III. Concentration of alkyl halide
IV. Aprotic solvents

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

Answer 1

The correct option is D Both I and III

$S_{N}1$ reactions are favored at low temperature whereas at high temperature $E_1$ reaction is favored.
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The nucleophile is not involved in the RDS in $S_{N}1$ reaction, thus it does not affect the rate of $S_{N}1$ reaction.
However, a stronger nucleophile may lead to side reactions. So, weak & moderate nucleophiles are preferred.
Rate of the reaction $\propto [R-X{]}^1[Nu{]}^0$

Polar protic solvent solvates the halide ion formed due to C-X bond breaking. Therefore, polar protic solvent favours the $S_{N}1$ reaction.
Hence correct option is d.