AVERAGE LOCAL IONIZATION ENERGIES COMPUTED ON THE SURFACES OF SOME STRAINED MOLECULES
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An ab initio selfconsistentfield molecular orbital (SCFMO) procedure has been used to compute the average local ionization energies [(r)] of some strained molecules on threedimensional surfaces defined by the contour of electronic density equal to 0.002 electrons/bohr3. (r) is rigorously defined within the framework of SCFMO 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 (r) values (Smin) on the surfaces of molecules are the sites expected to be the most reactive to electrophiles. We find Smin, near the CC bond midpoints of saturated threemembered, but not forumembered, hydrocarbon rings. These S,min are interpreted as reflecting the aromatic character of the former. Our (r) data effectively provide a fingerprint characterizing saturated threemembered 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. Copyright 1990 John Wiley & Sons, Inc.
