VARIABLE-TEMPERATURE INFRARED-SPECTROSCOPY OF CHLOROCARBONYL ISOCYANATE CL-CO-NCO AND THE EFFECT OF POLARIZABLE SUBSTITUENTS ON THE CONFORMATIONS OF CARBONYL ISOCYANATES AND ISOTHIOCYANATES

Variable temperature studies were performed on the gas phase infrared spectrum of chlorocarbonyl isocyanate. The conformeric band assignment s for several fundamental vibrations are compared with earlier analyse s. The higher stability of the transoid conformation for chloro- and b romocarbonyl isocyanate as well as for chloro- and bromocarbonyl isoth iocyanate is attributed to the high polarizabilities of the halogen at oms and explained as an electrostatic interaction between the heavy ha lides and the isocyanato carbon atom in the transoid conformation. The limitations of ab initio calculations in predicting the relative stab ilities and infrared frequencies of these molecules are discussed.