[thetada]

What does it really mean when we say that the inductive effect "stabilizes the positive charge" of a carbocation? I don't want to over-complicate the explanation for my students (A-level), so I'm thinking I should focus on the inductive effect, although I know hyperconjugation is also a factor.

I've been telling my students that the greater inductive effect of alkyl groups compared to H atoms slightly reduces the positive charge on the charged carbon atom, but suddenly I don't think that's accurate. The process makes sense to me in terms of charge segregation. Separating oppositely charged species requires energy and in primary carbocations the positively and negatively charged species are, in a sense, being held further apart than in a tertiary carbocation. So in fact it's not that the closer proximity of the electrons reduces the positive charge, but rather that less energy is required to produce an intermediate in which electrons are "allowed" to get closer to the positive carbon atom. Does that make any sense?

[Babcock_Hall]

I am not a physical organic chemist; however, here is how I look at induction.  The carbon atom bearing a positive charge in a methyl cation, for example, can only receive electron density from the three C-H bonds.  The carbon atom in a tert-butyl carbocation can receive electron density from three C-C bonds, and each of these three carbon atoms can receive electron density from three hydrogen atoms, which is nine hydrogen atoms altogether.

[thetada]

I agree that's a good way to rationalise the greater stabilizing effect of alkyl groups compared to hydrogen atoms, but I still don't understand how the availability of electrons affects the stability. If we think of lower stability intermediates requiring more energy, what is it about a reduced availability of "stabilizing electrons" that increases the energy demand?

[Archer]

I think it is due to the p-orbitals from the adjacent carbon. Due to the planar nature of the species the lobes are closer in proximity to the +ve charge.

If you could obtain a crystalline carbocation you would probably see the C⁺-C bond is shorter than a normal sigma bond.

Protons lack p-orbitals so have nothing to help stabilise the charge.

[thetada]

So would that lower the energy level of the electrons in the adjacent p-orbitals?