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Will 2-methylbutanal undergo aldol condensation?

We are taught that it will not because the +I effect makes the carbanion unstable, but if we make an enolate ion, isn't it resonance stabilized by the C=O group?

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There is no reason why the aldehyde cannot undergo an aldol reaction with itself. Enolates are not rendered unstable by the presence of additional alkyl substituents; in fact they are considered to be more stable. (See: formation of silyl enol ethers with $\ce{Et3N}$/$\ce{Me3SiCl}$.)

However, there is no way it can eliminate $\ce{H2O}$ to form the α,β-unsaturated ketone, since the aldol product does not have any α-hydrogens. Strictly you cannot call it an aldol condensation, although often no distinction is made in the literature between an aldol addition and a condensation.

Aldol product

The formation of the β-hydroxyketone above was reported as long ago as 1924, the reagent being potassium carbonate. More recently, in an attempt to make a 1,3-dioxolane from 2-methylbutanal with potassium t-butoxide and 2-chloroethanol, it was found that the enolisable aldehyde underwent "self-condensation" instead: Org. Lett., 2006, 8, 3745.

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