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Why do primary alkyl halides typically undergo SN2 substitution reactions more rapidly?

Answer 1

Consider the shrubbery around #H_3C-CH_2-X# versus #(H_3C)_2CHX# with respect to the ipso carbon.

The bond strength of a #2""^@# alkyl halide must be comparable to a #1""^@# alkyl halide. Enthalpy is thus not really a determinant. In terms of kinetics, the #1""^@# halide is a lot less sterically hindered, and thus substitution reactions should be a lot more favourable (and faster!) with this substrate.

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Answer 2

Paisley Boney

Primary alkyl halides typically undergo SN2 substitution reactions more rapidly due to the lower steric hindrance, allowing nucleophiles to approach and react more easily.

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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.