Why do tertiary halides react faster in SN1 mechanism but are slow to reactivity in an SN2 mechanism?

Answer 1

Well, #S_N2# processes are essentially bond-making reactions,......

.......whereas #S_N1# processes are essentially bond-breaking reactions., and of course, are only dependent on the concentration of the electrophile.

A bond making process at a tertiary carbon centre, for instance, is unlikely to be kinetically favoured, given the shrubbery around the #3^@# carbon.

On the other hand, this same shrubbery is likely to favour bond-breaking kinetically, and tend to stabilize a #3^@# carbocation, which is conceived to be an intermediate in an #S_N1# process :

#R_1R_2R_3C-X rarr R_1R_2R_3C^(+) +X^-#

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Answer 2

Easton Jones

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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.