Examination of Transannular Participation via SCF-MO Calculations and Far Ultraviolet Spectroscopy

Since the advent of the computer the chemist bas taken great strides in bringing the mathematical aspects of chemical systems up to date Before this time physical data on a tremendous number of different chemical systems had constantly been accumulating without theoretical backing. However, now with the tools available the chemist can at last begin the tedious and difficult task of explaining the data he has been receiving. One particular area of mathematical interest in chemistry is that which deals with the energy of a particular chemical system. In order to study this area of chemistry, theoretical or semiempirical energy calculations of these systems are necessary. Theoretical calculations are indeed very tedious and tend to discourage most chemists. However, working from Roothaan’s formulas for LCAO-SCF calculations Pariser and Parr and Pople came up with a semiempirica1 SCF-MO method. This method allows predictions of the ℼ-energy of molecules and the singlet transition energies. The P-P-P SCF method for determining ℼ-electron orbital energies and transition energies is quite analogous to the Hȕckel MO procedure except that it takes into account electron repulsions and •• attractions that the Hȕckel MO theory neglects. Indeed, the theory usually starts with the Hȕckel equations to get the starting LCAO wave functions. The purpose of this work was to study the possibility and magnitude of transannular ℼ-interaction in dimethylketen dimer, (1), tetramethylcyclobutane-1,3-biscyclohexylimine, (2), and tetramethylcyclobutane-1, 3dithione, (3). The approach was to use semiempirical SCF-MO calculations to determine ℼ-ℼ singlet transition energies and attempt to verify these by far ultraviolet spectroscopy