Question

Which of the following is correct?

• A. Vinyl chloride is more reactive than ethyl chloride in $S_{N}2$
• B. Vinyl chloride is more reactive than ethyl chloride in $S_{N}1$
• C. allyl chloride is less reactive than n-propyl chloride in $S_{N}1$
• D. allyl chloride is more reactive than n-propyl chloride in $S_{N}2$

Answer 1

Answer: (D)

As the electronegativity order of hybridized carbons is $sp>s{p}^2>s{p}^3$ so in an allylic halide, such as $C{H}_2=CH-C{H}_2-Cl$ , the alpha carbon is much more partially positive than the alpha carbon in(n-propyl chloride) ${\text{CH}}_{\text{3}}-{\text{CH}}_{\text{2}}-{\text{ CH}}_{\text{2}}-\text{Cl}$ . Therefore, the attacking nucleophile will be attracted to the alpha carbon more in the allylic halide compound than in the primary halide. It means allylic halides tend to follow $S_{N2}$ pathways more than primary halides.