The IR matrix isolation spectra and conformation energies of eight haloacetylhalides (CH2X-COY; X, Y = F, Cl, Br)

Abstract The nine possible haloacetylhalides (CH 2 X-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, ΔH o ( 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 ΔH o values were determined independently in the liquid state from Raman measurements.