What Does the Change in Direction of Alkyl Group Inductive Effects Mean?

In late 2024, we published the following paper, in which we suggested that the conventional position of alkyl groups as inductive electron-releasing groups (relative to hydrogen) is incorrect, and the actual effect is electron-withdrawing.

https://pubs.rsc.org/en/content/articlelanding/2024/ob/d4ob01572j

This paper has been very well received, and has led to the A level exam boards in the UK issuing communications that announce an upcoming review of the way alkyl groups electronic effects are taught in the A level curriculum.

I’ve recorded a 15 minute video giving my take on what this all means. The short answer, as we noted in the original paper, is that alkyl group electronic effects are much larger in charged species than in neutral molecules. In those cases, they are not strictly inductive effects, as polarizability becomes important. At that point, an alkyl group can be electron-withdrawing or electron-releasing by this mechanism. It’s just not an inductive effect!