IIT-JEE 2010 · Paper 1 · Chemistry Q10

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ChemistryMultiple correct+3Question 10 of 84

In the reaction phenol $\xrightarrow{\ce{NaOH(aq)/Br2}}$ the intermediate(s) is(are)

2,4-Dibromophenoxide ion: a phenoxide with Br ortho and para to O⁻.

4,4-Dibromocyclohexa-2,5-dien-1-one: a ring C=O with two Br on the para carbon.

4-Bromophenoxide ion: a phenoxide with Br para to O⁻.

3-Bromophenoxide ion: a phenoxide with Br meta to O⁻.

Answer and worked solution

Official answer: A, C

Bromination of phenoxide. In aqueous NaOH the phenoxide ion is very strongly activated, and bromine substitutes all ortho and para positions, finally giving 2,4,6-tribromophenol(ate).

Intermediates on the way:

(C) 4-bromophenoxide (first substitution, at the para position). Yes.
(A) 2,4-dibromophenoxide (second substitution, ortho). Yes.
(B) 4,4-dibromocyclohexadienone would need a second Br on the already substituted para carbon. No.
(D) The meta position is not activated. No.

(A), (C)

Topics:Phenols Aromatic hydrocarbons and electrophilic substitution

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IIT-JEE 2010 · Paper 1, Chemistry question 10