why do esters undergo nucleophilic acyl substitution?

[samstown]

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I don't quite get how esters are able to undergo nucleophilic acyl substitution reactions when the O-R adjacent to the carbonyl carbon is such a poor leaving group. The O in the leaving group is already quite electronegative and the R group which is electron donating makes the leaving group even more unstable.

 

[samstown]

oh, i think i found out why. the esters would have to be in an H+ solution such that the leaving group would be neutralized, correct?

 

[Rabolisk]

Or basic.

 

[orgohacks]

I don't quite get how esters are able to undergo nucleophilic acyl substitution reactions when the O-R adjacent to the carbonyl carbon is such a poor leaving group. The O in the leaving group is already quite electronegative and the R group which is electron donating makes the leaving group even more unstable.

You're right, under basic conditions a lot of nucleophiles wouldn't be powerful enough to displace it (e.g. Cl(-), AcO(-).

However, if your nucleophile is R2N(–) the reaction will go, because R2N(-) is an even worse leaving group than RO(-).

Under basic conditions, the O-R of the ester can also be replaced by O-H or another O-R, depending on conditions.