CBSE Class 12 · 2016 · Delhi · Haloalkanes and HaloarenesVery Short Answer

Of the two chlorides shown in the figure (2-chlorobutane and 1-chloro-2-methylpropane), which is more reactive towards the S

_{N}

1 reaction, and why?

Answer: 2-Chlorobutane — ionisation gives a 2° carbocation, more stable than the 1° carbocation from 1-chloro-2-methylpropane.

Solution

_{N}

1 rate is set by the stability of the carbocation formed in the slow ionisation step.
2-Chlorobutane → CH

_{3}

\overset{+}{C}HCH

_{2}

_{3}

(secondary carbocation).
1-Chloro-2-methylpropane → (CH

_{3}

)

_{2}

CHCH

_{2}^{+}

(primary carbocation).
2° > 1° in stability, so \textbf{2-chlorobutane reacts faster by S

_{N}

1}.

CBSE Class 12 Board · 2016 · Delhi · Subjective