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In the above mechanism's first step, what motivates the use of the carbanion resonance structure of the enolate ion if the negative charge is better localized on the more electronegative oxygen?

Edit: I might not have been clear in what motivates my confusion. Maybe I should rephrase what I'm asking. Basically, why would the carbon on the enolate attack the carbonyl carbon as opposed to the oxygen on the enolate attacking the carbonyl carbon? I assume there's a mixture of both products, but why is the aldol the major product?

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The negative charge is placed on the carbon atom to signify that it is the nucleophilic center which can attack the aldehyde. Indeed the negative charge is better placed on the oxygen atom, but after performing a nucleophilic attack on the aldehyde, an unstable acetal is formed reversibly.

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  • $\begingroup$ I understand that. I was looking for a deeper motivation as to why the carbanion resonance structure was the primary structure being shown. Is it possible the solvent choice would have it tending more towards carbanion character? $\endgroup$ – Shocked Feb 8 at 3:58
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    $\begingroup$ @orthocresol you're right, sorry for the mistake. I have edited my answer. $\endgroup$ – mck Feb 9 at 2:30
  • $\begingroup$ Maybe I should rephrase what I'm asking. Why would the carbon on the enolate attack the carbonyl carbon as opposed to the oxygen on the enolate attacking the carbonyl carbon? I assume there's a mixture of both products, but why is the major product? $\endgroup$ – Shocked Feb 9 at 15:31
  • $\begingroup$ Who is to say that the oxygen of the enolate doesn't add to the carbonyl group? If so, it is a non-productive step that forms a hemiketal which reverses to the reactants in base. So you are back where you started. $\endgroup$ – user55119 Feb 13 at 20:33

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