# Hydrogen isotope effect on methyl shift

Consider this typical 1,2 methanide shift in a carbocation:

Which isotopic form of methanide ($$\ce{CH3, CD3, or CT3}$$) would migrate from secondary carbocation to form more stable tertiary carbocation?

This link explains the mechanism but I could not understand the abstract.

Assuming that the migration of $$\ce{CH3-}$$ takes place, the following facts can be considered:

• The electronegativity of $$\ce{CH3}$$ is highest, thus, the formation of $$\ce{CH3->CH3-}$$ (methanide) is easiest. Consequently, the migration would be fastest in this case.

• The transition state would be most unstable in this case due to highest electronegativity of $$\ce{CH3}$$.

• The tertiary carbocation would be most stable in this case due to order of $$\mathrm{+I}$$ effect: $$\ce{CT3 > CD3 > CH3}$$

There are few exchanged comments below the second answer of this question and the proper explanation can be found in this link, which I can't access.

• @Safdar So, the stability of T.S. is more important than that of final carbocation. In your comment, the numerator and denominator are same. – Apurvium Sep 25 '20 at 8:50