Topological Effect on MO Energies

In the previous publicat ions [ 1 , 2 ] the theoret ical background of the topological effect on molecular orbital energies (TEMO) was worked out and illustrated with a number of ^-electronic carbocyclic and nitrogen heterocyclic molecules. The T E M O concept provides a general relation for the M O energy patterns of the S and T isomers. The S and T isomers are topologically related molecules generated by different linkages between bior mult i valent partial structures. In the case of bivalent i somorphic part ial structures with nonequivalent centers of residual valencies denoted by u and v. the S isomer is obtained linking u with w, and v with v. T h e T isomer results on connecting u with i\ and v with u. It was shown by analytical me thods [1] that in this case the difference A (.v) of the characterist ic polynomials of the T and S isomers is posit ive in the whole range of .Y which denotes the energy variable . Consequently, the Hückel M O energies of the S (i.e., e f ) and T (i.e., ej) isomer necessarily obey the following interlacing rule: