DIRECT OBSERVATION, REACTIONS UNDER MATRIX-ISOLATION CONDITIONS, AND ABINITIO CALCULATIONS FOR HALO(TRIFLUOROMETHYL)CARBENES - EVIDENCE FOR THE PHOTOCHEMICAL ADDITION OF A CARBENE TO DINITROGEN

Photolysis of 3-halo-3-(trifluoromethyl)diazirines (X = F (4), Cl (5), Br (6)) in an argon matrix at 12 K generates the respective singlet halo(trifluoromethyl)carbenes 1-3 which were characterized by infrared and ultraviolet spectroscopies and chemical trapping with HCl. Ab initio calculations indicate that all three carbenes should have singlet ground states, consistent with the experimental results. The vibrational spectrum for each carbene was determined using ab initio molecular orbital calculations and after appropriate scaling was in reasonable agreement with the experimentally determined one. The UV spectra calculated for the singlet carbenes using the configuration interaction with single excitations method gave excellent agreement with the experimental results. Extended photolysis (lambda > 280 nm) converts the carbenes to the respective alkenes. A nitrogen matrix gives identical results for 1 and 2, but 3 was found to add nitrogen photochemically to form the corresponding diazo compound.