JEE Main 2022 · 25 Jun · Shift 2 · Chemistry Q75

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ChemistrySingle correct+4 / -1Question 75 of 90

Amongst the following, the major product of the given chemical reaction is

3,4-Dihydro-2H-pyran treated with Br2 in CH3OH gives the major product.

trans-3-bromo-2-methoxytetrahydropyran (Br hashed at C-3,

\mathrm{OCH_3}

wedged at C-2)

cis-3-bromo-2-methoxytetrahydropyran (Br and

\mathrm{OCH_3}

both wedged)

trans-2-bromo-3-methoxytetrahydropyran (

\mathrm{OCH_3}

hashed at C-3, Br wedged at C-2)

trans-2-bromo-3-methoxytetrahydropyran (

\mathrm{OCH_3}

wedged at C-3, Br hashed at C-2)

Answer and worked solution

Official answer: A

Mechanism. $\mathrm{Br_2}$ forms a bromonium ion on the enol-ether C=C; methanol opens it at C-2, the carbon next to ring oxygen (oxocarbenium-stabilised), from the side opposite to Br.

Product. trans-3-bromo-2-methoxytetrahydropyran, structure (A).

(A)

Topics:Alkenes Geometrical isomerism Ethers

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JEE Main 2022 · 25 Jun · Shift 2, Chemistry question 75