Electronic structure of trans-alkyl nitroso-dimers

Calculations of the energy of the π-electron system of trans-(RNO)2, based on MO, VB, and NPSO wavefunctions have been carried out. Of these, the wavefunction most closely reproducing the results of a full Slater configuration interaction treatment was found to be one of the NPSO wavefunctions. This wavefunction explained well the dimerisation of nitrosoalkanes and the bond lengths of the dimer. A one-parameter wavefunction in which all configurations were included and were weighted exponentially according to their energies yielded a good zero-order approximation to the Slater configuration interaction ground state. A configuration interaction treatment based on Pariser–Parr-type approximations gave poor results.