THE CONFORMATIONAL EQUILIBRIA AND INFRARED MATRIX-ISOLATION SPECTRA OF CHLOROACETYL FLUORIDE AND BROMOACETYL FLUORIDE

Infrared spectra of chloroacetyl fluoride and bromoacetyl fluoride were investigated in argon and nitrogen matrices at 14 K with nozzle temperatures from 313 to 700 K. After annealing to 30-34 K the spectra changed considerably and the high energy conformer (gauche) nearly vanished. Raman spectra of the liquids were recorded at var-ious temperatures and as amorphous and crystalline solids. The enthalpy differences were found to be DELTAH0 (gauche - anti) = 6.5 +/- 0.4 kJ mol-1 in chloroacetyl fluoride and 4.9 +/- 0.4 kJ mol-I for bromoacetyl fluoride. The matrix spectra recorded at different nozzle temperatures gave lower DELTAH0 values than reported from isothermal vapour cells, indicating that the high energy conformer (gauche) was partly converted to anti during deposition due to the low gauche-anti barrier.