[Conceptual OChem] With reactions of carbonyls and bases, how do you determine i

Question

[Conceptual OChem] With reactions of carbonyls and bases, how do you determine if the base will 1) perform a nucleophilic attack on the carbonyl carbon, followed by protonation of the O-, or 2) immediately protonate the alpha hydrogens?

I've linked a photo of a reaction that I had to draw the mechanism for (having issues with uploading it through chegg), and ended up with two mechanisms due to the two above possibilities. Which one is the correct mechanism? Or are both mechanisms correct, and will the final product be a mixture?

Link to the two mechanisms I drew: https://imgur.com/a/WuLbZ

Explanation / Answer

Organic chemistry

CH3O- is a strong base and therefore if we have an acidic hydrogen in proximity, like the one here having a secondary carbon having a H atom, the base would preferentially pick the hydrogen in the first step to generate an enolate intermediate. The enolate will reform C=O bind and intramolecular cyclization occurs. The formation of hemiketal under basic condition in such an case is the less preferred mechanism.

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