# Is the concept of frontier orbital interactions chiefly a kinetic concept?

Frontier molecular orbital theory has proved to be an immensely useful concept. The concept of HOMO-LUMO interactions are frequently employed in detailing the mechanistic descriptions of reactions in organic chemistry. It seems to me that there are numerous examples of HOMO-LUMO interactions seem to be responsible for kinetic phenomena.

For example, secondary orbital interactions allow the preference for the endo product in the Diels-Alder reaction under kinetic control.

Nucleophilicity, which is often linked to the energy of the HOMO of the nucleophile, is also often regarded as a kinetic phenomenon. In fact, Lewis basicity itself may even be seen as a kinetic concept. For example, we make the assertion that phosphine is a better nucleophile (and also better Lewis base) compared to ammonia because $$\ce {P}$$ is less electronegative than $$\ce {N}$$ and thus, the HOMO of $$\ce {PH3}$$ is thus higher in energy, compared to that of $$\ce {NH3}$$.

Should we thus classify frontier orbital interactions as a kinetic concept?

• This apply in thermochemistry as well once you are under kinetic control. – Alchimista Dec 27 '18 at 9:10