Master Organic Chemistry Reaction Guide

Addition of Grignard reagents to aldehydes to give secondary alcohols

Description: Addition of a Grignard reagent to an aldehyde results in a new C–C bond an a secondary alcohol after addition of acid.
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8 thoughts on “Addition of Grignard reagents to aldehydes to give secondary alcohols

    1. The Mg adds by oxidative insertion to the Br to form the Grignard. Then, that reacts with the carbonyl carbon – yes.

  1. With a formaldehyde instead of an aldehyde, I assume the main product will lose one of its R’s and instead have an H, right?

  2. I wonder:
    Why grignard reagent does not act as a nucleophile when an alkyl halide is the electrophile.
    Why acetylide ion attacks alkyl halides well, but not acyl groups?

    1. Acetylide ions will attack acyl groups.

      Re: grignard reagents, they tend to be clusters in solution and also equilibrate between various forms (Schlenk equilibrium). What often happens is that you see them acting as a base (breaking C-H) or pumping electrons into the alkyl halide via single electron transfer. Substitution reactions to break C-X are more sterically demanding (have to overlap with C-X sigma-star orbital) and this process is slower than the other pathways.
      Much better to use copper reagents (organocuprates) which don’t suffer from these problems as much.

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