Question

How would you explain what a 1,2-alkyl shift is?

Answer 1

Well, the name tells you most of the details.

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A 1,2-alkyl shift is a shift of an alkyl group to an adjacent carbon atom (i.e. 1,2 to the original position).

This tends to occur to stabilize a carbocation intermediate in first-order reactions (e.g. `S_N1`, `E1`).

In this case, this is in lieu of a 1,2-hydride shift, since there are no `"H"` atoms on the same carbon from which the alkyl group started (as you should expect from a quaternary carbon!).

A more substituted carbocation is more stable, due to the hyperconjugation from a greater number of electron-donating groups (e.g. holding negative partial charge) surrounding an electropositive atom (i.e. holding positive partial charge).