THE IR MATRIX-ISOLATION SPECTRA AND CONFORMATIONAL ENERGIES OF 8 HALOACETYLHALIDES (CH2X-COY - X,Y=F,CL,BR)

The nine possible haloacetylhalides (CH2X-COY; X, Y = F, Cl, Br) except fluoroacetylfluoride were studied by matrix isolation spectroscopy in the IR region 4000-200 cm-1 (1:500 ratio) in argon and nitrogen matrices. With an electrically heated quartz nozzle, vapour mixtures at different temperatures between 300 and 900 K were deposited on the window at 14 K. Assuming the thermodynamic equilibrium between the conformers to be maintained in the matrix at the window, ΔHo(gauche-anti) were calculated from van't Hoff plots of several pairs of anti and gauche bands. By annealing the matrices to 30-36 K, the gauche bands nearly vanished, indicating barriers of the order 6-7 kJ mol-1, except for fluoroacetylchloride and fluoroacetylbromide for which the barrier must be above 11-12 kJ mol-1 since the thermodynamic equilibrium was not achieved at the annealing temperature. The ΔHo values were determined independently in the liquid state from Raman measurements. © 1990.