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leaving groups.

In an acyl substitution reaction, which of the following would be expected to be the best leaving group?PhosphateChlorideHydroxyl.
I know chloride is the answer its just why which is doing my head in.
So lecture content says that a weak base is considered a 'good' leaving group. and that the weak base is the conjugate base of a strong acid.

my textbook states that the most electronegative group is the best leaving group

which reason am I supposed to use to back up the answer because they are both stating different things. hope this makes sense
(edited 1 year ago)
The best leaving group is likely to be the one which can best stabilise a negative charge. If the leaving group is able to form resonance hybrids then this will help it leave as it will stablise the negative charge.

Phosphoric acid is a weak acid, so its conjugate base PO43-will be a strong base. The hydroxide ion , as it would be if the hydroxyl group was to leave would form the hydroxide ion, which is a poor leaving group since it is a strong base.

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