Which of the following statements about the enolate ion CH2=C(CH3)-O^- derived from propanone are correct?

Alkylation with CH3I occurs mainly at carbon and gives butan-2-one.

Protonation on oxygen gives prop-1-en-2-ol, which tautomerises to propanone.

The negative charge is delocalised over oxygen and the alpha carbon, with the larger share on oxygen.

Alkylation with CH3I occurs mainly at carbon and gives butan-2-one.

Protonation on oxygen gives prop-1-en-2-ol, which tautomerises to propanone.

The alpha carbon is sp^3 hybridised and pyramidal.

The negative charge is delocalised over oxygen and the alpha carbon, with the larger share on oxygen.

JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g3080

Which of the following statements about the enolate ion $CH X_{2} = C (CH X_{3}) - O X^{-}$ derived from propanone are correct?

AAlkylation with $CH X_{3} I$ occurs mainly at carbon and gives butan-2-one.
BProtonation on oxygen gives prop-1-en-2-ol, which tautomerises to propanone.
CThe alpha carbon is $s p^{3}$ hybridised and pyramidal.
DThe negative charge is delocalised over oxygen and the alpha carbon, with the larger share on oxygen.

The enolate is an allyl-like system

C = C - O X^{-} \leftrightarrow X_{-} X_{2}^{2 -} C - C = O

with more charge on the electronegative oxygen. The alpha carbon is part of the pi system, so it is

s p^{2}

and planar, which rules out the last statement. With soft electrophiles such as

CH X_{3} I

it reacts at carbon. O-protonation gives the enol, which rapidly tautomerises to the more stable ketone.