How many different enolate ions can 3-methylpentan-2-one, CH3-CO-CH(CH3)-CH2CH3, form by removal of one alpha proton, if the E and Z isomers of an enolate are counted as different species?

JEE Advanced levelSingle correct optionDifficulty 3 of 3g3073

How many different enolate ions can 3-methylpentan-2-one, $CH X_{3} - CO - CH (CH X_{3}) - CH X_{2} CH X_{3}$ , form by removal of one alpha proton, if the E and Z isomers of an enolate are counted as different species?

The alpha carbons are C-1 (the

CH X_{3}

) and C-3 (the

CH

). Removing a C-1 proton gives one enolate,

CH X_{2} = C (O X^{-}) - CH (CH X_{3}) CH X_{2} CH X_{3}

, which has no E/Z isomerism because the terminal carbon carries two H. Removing the C-3 proton gives

CH X_{3} - C (O X^{-}) = C (CH X_{3}) CH X_{2} CH X_{3}

, whose C=C has different groups on both carbons, so E and Z forms exist. Total

1 + 2 = 3