Applications of Calculated Local Surface Ionization Energies to Chemical Reactivity. (Reannouncement with New Availability Information).

摘要

The average local ionization energy I(r), is discussed in relation to chemical reactivity. l(r) is defined within the framework of SCF-MO theory and is interpreted as the average energy required to remove an electron from any point r in the space of a molecule. A survey of applications of ab initio SCF I(r) computed on molecular surfaces defined by the 0.002 electron/ bohr3 contour of the electronic density is presented. The positions at which the surface I(r) has its lowest values (IS,min) are indicative of sites most reactive toward electrophiles. An excellent correlation has been found between the ring carbon IS,min of monosubstituted benzenes and the Hammett constants. For a large variety of carbon, oxygen and nitrogen acids, we have shown that good correlations exist between pKa and the conjugate base ISmin. A good relationship is demonstrated to exist between the conjugate base ISmin of substituted acetic acids and the inductive substituent constants (which were derived from pKa's). IS, min found near the C-C bond midpoints of the three-membered ring positions of saturated strained hydrocarbons are interpreted as reflecting the a-aromaticity of these rings. local surface ionization energies, chemical reactivity, Hammett constants, acidities