Why is Cl a better leaving group than an anhydride?

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SUMMARY

Chloride (Cl-) is a superior leaving group compared to anhydrides (R-COOCO-R') when adjacent to a carbonyl group. This is due to the stability of the chloride ion and its ability to stabilize the transition state during nucleophilic substitution reactions. While anhydrides benefit from resonance stabilization, the overall molecular interactions and the reaction environment favor chloride as the more effective leaving group in these scenarios.

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nobahar
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Hello!
I just read that chloride is a better leaving group than an anhydride (when adjacent to a carbonyl, hence the anhydride). (i.e. R-COCl, an Acyl chloride and R-COOCO-R', an anhydride).
I do not understand why this is so. A good leaving group is characterized by being electron withdrawing and a stable anion. Oxygen is more electronegative and a carboxyl group has resonance, which chloride doesn't.
I'd then conclude that the anhydride is a better leaving group; but apparently not!
Any help appreciated.
 
Physics news on Phys.org
Instead of just thinking about the leaving group as a discrete entity, think about the molecule as a whole, and about what interactions can be taking place between the LG and the reaction center.
 

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