Structure and Energetics of Simple Carbenes CH2, CHF, CHCl, CHBr, CF2, and CCl2

Abstract

There is very little experimental data concerning the singlet-triplet separations of carbenes. In many cases, it is not even possible to form estimates of this separation from experimental results. CH2 is a distinct exception; here substantial, although contradictory, data are available. The equilibrium geometries of the lowest singlet states of several carbenes have been determined experimentally. However, the geometries of many states are not known and the triplet state geometries are also generally unknown. In order to obtain theoretical information about these quantities for a series of halogenated carbenes, we have studied CH2, CHF, CHCl, CHBr, CF2, and CCl2 using a consistent level of ab initio electronic structure theory. One configuration (triplet state) and two configuration (singlet state) wave functions have been computed. Double ζ basis sets augmented by a d function on the carbon atom, optimized separately for both the singlet and triplet states of each molecule, were used. The theoretical equilibrium geometries agree well with the available experimental data. The trends of the singlet-triplet separations are discussed and correlated with the carbon atom Mulliken gross populations for the singlet and triplet states. © 1977, American Chemical Society. All rights reserved.