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I added 2 equiv of p-tolualdehyde to 1 equiv of acetone to make (1E, 4E)-1,5-di-p-tolylpenta-1,4-dien-3-one (NMR backed it up). Why is this the only isomer formed? Just sterics or something more?

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    – Community Bot
    Commented Nov 23, 2022 at 22:36

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If your Claisen condensation was run with lots of heat (reflux?), as is typical, then you will obtain the thermodynamic product. For the alkenes, the (E)-isomer is more thermodynamically stable (because of sterics) so predominates under these conditions.

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