Bromination of Hydrocarbons. IV. Photochemical and Thermal Bromination of Neopentane in the Gas Phase. The C–H Bond Strength in Neopentane

Abstract

The homogeneous photochemical bromination of neopentane was studied in the temperature range 98° to 152°C and found to proceed through an atom and radical chain mechanism analogous to the bromination of methane and ethane. Hydrogen bromide inhibits photobromination of neopentane much more than it does in the case of methane, increasing in its effect with rising temperature. Thermal bromination was studied at 197°C and found to take place by a mechanism analogous to the photochemical reaction, the bromine atoms being produced thermally rather than photochemically. The corrected activation energy of the overall reaction was determined from the temperature coefficient of the photochemical reaction and found to be 17.8 kcal/mole. Questions of the efficiencies of various molecules as third bodies in the homogeneous recombination of bromine atoms and problems relating to steric effects in atom and radical reactions have been discussed. The C–H bond strength in neopentane has been estimated to be 95.5 kcal/mole at room temperature.