Kinetics and Thermochemistry of the sec-C4H9 + HBr n-C4H10 + Br Equilibrium

Article abstract of DOI:10.1021/j100382a041

The kinetics of the sec-C4H9 + HBr reaction was studied in a tubular reactor coupled to a photoionization mass spectrometer.The sec-C4H9 radicals were produced homogeneously in the reactor by pulsed UV laser photolysis.Radical decays in the presence of different HBr concentrations were monitored in time-resolved experiments.Rate constants were obtained as a function of temperature (229 - 533 K) and were fit to an Arrhenius expression: 1.7(+/-0.6)*10^-12exp<4.8(+/-1.3)kJ mol^-1/RT> cm³ molecule^-1 s^-1.This kinetic information was combined with knowledge of the rate constant of the reverse reaction to obtain both the entropy <343 (+/-9) J mol^-1 K^-1> and heat of formation <66.7 (+/-3.0) kJ mol^-1> of the sec-C4H9 radical at 298 K in a second law determination.The secondary C-H bond energy in n-C4H10 derived from this heat of formation is 411 (+/-3) kJ mol^-1.This value is in excellent agreement with the secondary C-H bond energy in C3H8 determined previously both in an investigation of a comparable equilibrium involving HBr <410(+/-5) kJ mol^-1> and in investigations of dissociation-recombination equilibria involving i-C3H7 <410(+/-3) kJ mol^-1>.This study also provides a reconciliation of the formerly disparate sec-C4H9 heats of formation that were derived from studies of differnet kinds of chemical equilibria.