If stability order of P, Q and R is - P Q R, then correct statement is :

Question

If stability order of P, Q and R is - P > Q > R, then correct statement is :

TestHub · Accepted Answer

Stability: Acid-catalyzed dehydration of 3-methyl-2-butanol proceeds via an E1 mechanism involving a carbocation intermediate and rearrangement to form the most stable alkenes. The possible alkenes are:

P: 2-methylbut-2-ene ( $C H_{3} C (C H_{3}) = C H C H_{3}$ , tetrasubstituted)

Q: 2-methylbut-1-ene ( $C H_{3} C H_{2} C (= C H_{2}) C H_{3}$ , trisubstituted)

R: 3-methylbut-1-ene ( $C H_{2} = C H C H (C H_{3})_{2}$ , monosubstituted)

The stability order is $P > Q > R$ .

(A) Alkene P is achiral, and anti-addition of $B r_{2}$ yields a racemic mixture of 2,3-dibromo-2-methylbutane.

(B) Alkene Q is achiral, and addition of $B r_{2}$ yields a racemic mixture of 1,2-dibromo-2-methylbutane, which is not a meso product.

(C) Alkene R reacts with $H Cl$ via a planar carbocation intermediate. Nucleophilic attack from either face yields a racemic mixture of 2-chloro-3-methylbutane. Thus, racemization occurs. (D) Markovnikov's rule is applicable to alkene R, as it is an unsymmetrical alkene. The correct answer is option (C)

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