Question

Assertion: Chlorination of allylic hydrogen is more difficult than vinylic hydrogen.
Reason: Allyl radical is stabilized by resonance.
A. Both assertion and reason are correct and reason is the correct explanation for assertion.
B. Both assertion and reason are correct and reason is the correct but the reason is not the correct explanation for the assertion.
C. Assertion is correct, reason is incorrect.
D. Assertion is incorrect, reason is correct.
E. Both assertion and reason are incorrect.

Answer 1

Understand the difference between the allylic and vinylic carbon. The allylic carbon is that carbon which is located adjacent to the double bond. Whereas the vinylic carbon shares the double bond with another carbon.

Complete step by step answer:
Allylic halogenation is easier than vinylic halogenation since there is a resonance of the bond which stabilizes the compound. And as we discussed earlier that allylic carbon is located adjacent to the double bond. And vinylic carbon has a double bond between the two carbons. Now let’s understand the mechanism, when the hydrogen atom of the allylic carbon is replaced by a halogen like bromine, chlorine, fluorine etc. that process is known as the allylic or vinylic halogenation. So here the hydrogen atom is replaced by the chlorine atom therefore this reaction is known as chlorination of allylic or vinylic hydrogen. To understand the reaction we should know the reagent, condition and substrate with which the reaction took place.
The correct answer is D the assertion is incorrect and the reason is correct.

Additional information:
If we want to do an allylic chlorination we must take an alkene for example propene when this alkene reacts with chlorine the product obtained is 3-chloropropene and the by product is HCL. We can also use sulphuric chloride in place of chlorine, the only difference will be that with chlorine we will need the temperature of $773k$ and with sulphuric chloride being more reactive we would need only $475k$ and a peroxide like benzoyl peroxide.

Note: This reaction as mentioned above is known as halogenation. There are different types of halogenation free radical, ketone, etc. This reaction mechanism comes under the name of electrophilic addition. Unsaturated compounds like alkene or alkynes, in case of alkenes there’s an intermediate used like halonium ion.