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Why are sulfate ion and p‐toluenesulfonate (tosylate ion) good leaving groups?

Answer 1

The methyl sulfate and p‐toluenesulfonate ions are good leaving groups because they are weak bases and are stabilized by resonance.

Good leaving groups are weak bases. They don't want to share their electrons.

For example, the #"p"K_"a"# of p‐toluenesulfonic acid is -2.8. The #"p"K_"b"# of its conjugate base, p‐toluenesulfonate ion, is 16.8 — a very weak base.

These ions are stabilized by resonance, and that also makes them good leaving groups.

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Answer 2

Zoe Alexander

Sulfate ion and p-toluenesulfonate (tosylate ion) are good leaving groups due to their stability after departure, facilitated by resonance stabilization and the ability to disperse the negative charge.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.