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Ester Enolates

In Chapter 18 we introduced the enolates of aldehydes and ketones (review) and looked at their reactions as C nucleophiles (review).  These enolates were formed by treating the aldehyde or ketone with a suitable base :

formation and resonance stabilisation of a ketone enolate

Now we will investigate another group of carbonyl containing compounds, the esters, which behave in a very similar fashion.....

When preparing ester enolates, the base is normally chosen to match the alcohol portion of the ester...
So if you have:
a methyl ester, RCOOCH3 you use methoxide, -OCH3, or,
an ethyl ester, RCOOCH2CH3 you use ethoxide, -OCH2CH3

This avoids problems caused by transesterification (conversion of one ester into another)......

or hydrolysis......

Note that in both cases the problem arises because the base reacts as a "nucleophile"

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© Dr. Ian Hunt, Department of Chemistry, University of Calgary