Kinetics and thermochemistry of the reactions of alkyl radicals (methyl, ethyl, isopropyl, sec-butyl, tert-butyl) with hydrogen iodide: a reconciliation of the alkyl radical heats of formation

摘要: The kinetics of the reactions CH{sub 3}, C{sub 2}H{sub 5}, i-C{sub 3}H{sub 7}, s-C{sub 4}H{sub 9}, and t-C{sub 9} with HI were studied in a tubular reactor coupled to photoionization mass spectrometer. Rate constants measured as function temperature (typically between 295 648 K) determine Arrhenius parameters. These results combined determinations rate reverse (I + hydrocarbon) determined previously by others obtain equilibrium for following reaction: R {leftrightarrow} R-H I. Second Third Law based analyses using these yielded heats formation five alkyl radicals whose studied. (obtained calculated entropies) are extremely accurate, within {plus minus} 2 kJ mol{sup {minus}1} current best values. cause long-standing disparity that has existed derived from studies I equilibria those obtained investigation dissociation-recombination been identified. It is difference assumed generic activation energy (4 kJmore » {minus}1}) had used all prior thermochemical calculations actual values energies. A complex mechanism consistent observed kinetic behavior discussed.« less