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How's a ketone made up of a pair of optical isomers?

A compound, Q, gives an orange precipitate with 2,4dinitrophenylhydrazine.
Compound Q is resistant to oxidation.On reduction, Q gives a product made up of a pair of optical isomers.
Which of the following compounds could be compound Q?

A) CH3CH2CH2COCH3

B) CH3CH=CHCH(OH)CH3

C) CH3CH2CH2CH2CHO

D) CH3CH2COCH2CH3

So A is a ketone, B is an alcohol, C is an aldehyde and D is ketone.
Brady's reagent is only for aldehydes and ketones, but because Compound Q is resistant to oxidation, it's a ketone so it's either A or D.

Now my question is that it says that Q gives a product made up of a pair of optical isomers .. but neither A or D consist of 4 different groups, so how's that?

Reply 1

Pigster

When reduced (e.g. with NaBH4) the ketone will convert to an alcohol.

D makes pentan-3-ol, the central carbon is attached to 1xH, 1xOH, 2xC2H5.

A makes pentan-2-ol, the carbon at position 2 is attached to 1xH, 1xOH, 1xCH3, 1xC3H7, i.e. four different groups, so can be chiral. The attack by the H- ion can happen on either side of the ketone, which is planar around the C=O.