JEE Advanced 2019 · Paper 1 · Chemistry Q12 · Dronacharya Exams

My attemptsTake a paper

← JEE Advanced 2019 · Paper 1

ChemistryMultiple correct+4 / -1Question 30 of 54

Choose the correct option(s) for the following set of reactions

C₆H₁₀O with (i) MeMgBr, (ii) H₂O gives Q. Q with conc. HCl gives S (major). Q with 20% H₃PO₄ at 360 K gives R (major). R with (i) H₂, Ni, (ii) Br₂, hν gives T (major). R with HBr and benzoyl peroxide, Δ, gives U (major).

A

S: 6-chloro-1-methylcyclohexene (CH₃ on the ring C=C, Cl on the adjacent CH); T: 1-bromo-1-methylcyclohexane.

B

U: 1-bromo-1-methylcyclohexane; S: 1-chloro-2-methylcyclohexane.

C

S: 1-chloro-1-methylcyclohexane; U: 1-bromo-2-methylcyclohexane.

D

U: 1-bromo-2-methylcyclohexane; T: 1-bromo-1-methylcyclohexane.

Answer and worked solution

Official answer: C, D

$\ce{C6H10O}$ is cyclohexanone.

The intermediates.

Q. $\ce{MeMgBr}$ gives 1-methylcyclohexanol.
S. Conc. HCl substitutes by $\ce{S_N1}$ at the tertiary carbon, giving 1-chloro-1-methylcyclohexane.
R. $\ce{H3PO4}$ dehydrates Q to the more substituted alkene (Saytzeff), 1-methylcyclohexene.
T. $\ce{H2/Ni}$ gives methylcyclohexane, and $\ce{Br2}/h\nu$ brominates the tertiary C-H, giving 1-bromo-1-methylcyclohexane.
U. HBr with peroxide adds anti-Markovnikov, giving 1-bromo-2-methylcyclohexane.

The options.

(A) has the wrong S.
(B) has the wrong S and U.
(C) S and U are both correct.
(D) U and T are both correct.

(C), (D)

Topics:Alcohols Nucleophilic addition Alkenes Alkanes

← Previous question Next question →