Average local ionization energies computed on the surfaces of some strained molecules

Abstract

An ab initio self-consistent-field molecular orbital (SCF-MO) procedure has been used to compute the average local ionization energies [Ī(r)] of some strained molecules on three-dimensional surfaces defined by the contour of electronic density equal to 0.002 electrons/bohr3. Ī(r) is rigorously defined within the framework of SCF-MO theory and can be interpreted as the average energy needed to ionize an electron at any point in the space of a molecule. Thus, the positions of the smallest Ī(r) values (ĪSmin) on the surfaces of molecules are the sites expected to be the most reactive to electrophiles. We find ĪSmin, near the CC bond midpoints of saturated three-membered, but not foru-membered, hydrocarbon rings. These ĪS,min are interpreted as reflecting the “σ-aromatic” character of the former. Our Ī(r) data effectively provide a “fingerprint” characterizing saturated three-membered rings, which is useful, for example, in analyzing molecules such as [1.1.1] propellane. Our results for the latter are consistent with the interpretation of it having a biradical character, as has been suggested earlier.