Each of the following optically active ketones/aldehydes is kept in aqueous NaOH at room temperature. Select those that lose their optical activity by racemisation through an enolate.

Racemisation by enolisation needs the stereocentre to be the alpha carbon carrying an H, since removal of that H gives a planar enolate. (S)-3-Methylpentan-2-one (C3 alpha, has H) and (S)-2-phenylpropanal (C2 alpha, has H) racemise. In 4-methylhexan-2-one the stereocentre is beta to C=O, and in 2-methyl-2-phenylbutanal the alpha carbon is quaternary (no alpha H), so these retain their configuration.