Question

Assertion: In comparison to ${C_2}{H_5}Br$, it is difficult to carry out the ${S_N}1$ reaction on vinyl bromide.
Reason: Vinyl group is an electron donating group
(A) Both assertion and reason are correct and the reason is the correct explanation for the assertion.
(B) Both assertion and reason are correct but reason is not the correct explanation for the assertion.
(C) Assertion is correct but the reason is incorrect.
(D) Assertion is incorrect but the reason is incorrect.

Answer 1

In order to find whether the assertion and reason are correct or incorrect, we must be first aware of what an alkyl and vinyl halide is. Alkyl halide is a chemical compound in which the halogen group will be attached to one of the carbons in the alkane group. While vinyl halide is a chemical compound in which the halogen group is attached to one of the carbons present in the alkene group.

Complete Solution :
Let us first understand about alkyl halide and vinyl halide and then see why alkyl halide like ${C_2}{H_5}Br$ undergo ${S_N}1$ reaction while why it is difficult to carry out ${S_N}1$ reaction in vinyl halide. First is alkyl halide.
- Alkyl halide is a chemical compound in which the halogen group will be attached to one of the carbons in the alkane group. The carbon atom attached to the halogen group in alkyl halide will be having $s{p^3}$hybridisation. It does not undergo any delocalisation. Therefore, it will not be having any resonance structure. So, we can say that alkyl halide is highly reactive. It will be easier to carry out unimolecular nucleophilic substitution reactions in alkyl halides like ${C_2}{H_5}Br$.
- Vinyl halide is a chemical compound in which the halogen group is attached to one of the carbons present in the alkene group. The carbon atom to which the halogen group is attached will be having $s{p^2}$hybridisation. Due to the presence of double bonds it can undergo delocalisation. It will be having resonance structure and hence, the vinyl halide is less reactive. Therefore, it will be difficult to carry out the ${S_N}1$ reaction.
Hence the Assertion is correct but the reason is wrong.
So, the correct answer is “Option C”.

Note: Let us see some of the properties and uses of alkyl halides. They are:
Properties:
- Alkyl halides are colorless
- odorless
- It is hydrophobic in nature.
Uses:
- Alkyl halides are uses in fire extinguishers
- in refrigerants
- Pharmaceuticals
- Flame retardants.