JEE Main · 2021 · 17 Mar 2021 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

Mesityl oxide is a common name of:

(A)2,4- Dimethyl pentan-3-one
(B)3-Methyl cyclohexane carbaldehyde
(C)2-Methyl cyclohexanone
(D)4-Methyl pent-3-en-2-one✓ Correct

Answer: (D)

Solution

Mesityl oxide is the dehydration product of diacetone alcohol, the aldol of acetone. Loss of water from

(C H_{3})_{2} C (OH) C H_{2} COC H_{3}

gives the conjugated enone

(C H_{3})_{2} C = CHCOC H_{3}

. Numbering the five-carbon chain from the carbonyl end puts the ketone at C-2, the double bond between C-3 and C-4 and a methyl branch at C-4, so mesityl oxide is 4-methylpent-3-en-2-one.

JEE Main · 2021 · 17 Mar 2021 · Shift 1 · Single correct option

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