Which is the #alpha-"carbon"# in a ketone, or ester?

1 Answer
anor277
Aug 24, 2017

The #sp^3# hybridized carbon is regarded as the #alpha-"carbon"#

Explanation:

Why? Because in esters, this is the carbon that can be enolized.....

#H_3C-C(=O)OCH_3 stackrel("base")rarrH_2C=C(O^(-))OCH_3#

The enolate of course undergoes #"keto-enol tautomerism"#, and remains the premier means of #C-C# bond formation. Because the negative charge is delocalized over three centres, it is somewhat stabilized.

#H_2C=C(O^(-))OCH_3harr""^(-)H_2C-C(=O)OCH_3#

And for diacids, and diesters, such as malonic acid, and ethyl acetoacetate, the hydrogens of the #alpha-C# are readily enolizable.

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