Hydrogen-atom abstraction from alkanes by hydroxyl radical. 6. Cyclopentane and cyclohexane

Abstract

H20 + 02 reaction. However, it is unlikely that a hydrogen-bonded intermediate can produce a negative temperature dependence for the atom + H02 reactions in Figure 10 as atoms possess no permanent dipole moment. Alternatively, it does not appear necessary to invoke a long-range attraction for these atom + H02 reactions since only the Cl + H02 -HC1 + 02 reaction exhibits a negative temperature dependence, and indeed only a negligible one within experimental error.31 More likely, the explanation for the somewhat large A factors for the X + H02 -<• HX + 02 series lies in the Hammond postulate, which in essence states that the transition state of a direct reaction increasingly resembles reactants as the exothermicity of the reaction increases.32 The X + H02 -»-HX + 02 reactions, with unusually large exothermicities (40 kcal mol"1 greater than the X + H202 counterparts), would thus be expected to have somewhat large A factors as the transition states would occur early along the reaction coordinate.The following picture then emerges for the reactions of H02 with radicals. Formation of the (XOOH)* complex is a rapid process, occurring at or near the gas kinetic rate. At high pressure, this intermediate can undergo collisional stabilization, but at low pressure the lifetime of the excited Complex is long enough for the excess energy to induce bond breakage of either the H-O bond (reformation of reactants) or the 0-0 bond (formation of XO and OH products). Much slower is the direct attack on the hydrogen atom to form the HX and 02 products; however, this

Kinetics of the gas-phase reactions of OH radicals with alkanes and cycloalkanes

“…Rate constants are available from the absolute rate studies of Jolly et al (1985), Droege and Tully (1987), Bott and Cohen (1989) and Donahue et al (1998) and from the relative rate studies of Volman (1975), Darnall et al (1978), Atkinson et al (1982a), Kramp and Paulson (1998) and DeMore and Bayes (1999). The study of Atkinson et al (1982a) is judged to supersede the earlier study of Darnall et al (1978), and Fig.…”

“…The study of Atkinson et al (1982a) is judged to supersede the earlier study of Darnall et al (1978), and Fig. 20 shows an Arrhenius plot of the data of Atkinson et al (1982a), Jolly et al (1985), Droege and Tully (1987), Bott and Cohen (1989), Kramp and Paulson (1998), Donahue et al (1998) and DeMore and Bayes (1999). There is an appreciable amount of scatter in the measured room temperature rate constants, with the rate constant of Kramp and Paulson (1998) relative to 1,3-butadiene being lower than the other rate data, and the absolute rate constants of Donahue et al (1998) are both quite scattered and generally higher than the rate constants of Atkinson et al (1982a), Jolly et al (1985), Droege and Tully (1987), Kramp and Paulson (1998) (including those relative to n-nonane, propene and trans-2-butene), and DeMore and Bayes (1999).…”

“…20 shows an Arrhenius plot of the data of Atkinson et al (1982a), Jolly et al (1985), Droege and Tully (1987), Bott and Cohen (1989), Kramp and Paulson (1998), Donahue et al (1998) and DeMore and Bayes (1999). There is an appreciable amount of scatter in the measured room temperature rate constants, with the rate constant of Kramp and Paulson (1998) relative to 1,3-butadiene being lower than the other rate data, and the absolute rate constants of Donahue et al (1998) are both quite scattered and generally higher than the rate constants of Atkinson et al (1982a), Jolly et al (1985), Droege and Tully (1987), Kramp and Paulson (1998) (including those relative to n-nonane, propene and trans-2-butene), and DeMore and Bayes (1999). A least-squares analysis of the rate constants of Atkinson et al (1982a), Jolly et al (1985), Droege and Tully (1987), Bott and Cohen (1989), Kramp and Paulson (1998), Donahue et al (1998) and DeMore and Bayes (1999), using the expression k=AT 2 e −B/T , leads to the recommendation of…”

“…20). A least-squares analysis of the rate constants of Atkinson et al (1982a), Jolly et al (1985), Droege and Tully (1987), Bott and Cohen (1989), Kramp and Paulson (1998) (only the rate constants relative to n-nonane, propene and trans-2-butene, because of the possibility that 1,3-butadiene reacted significantly with NO 2 and/or O( 3 P) atoms, Kramp and Paulson, 1998) and DeMore and Bayes (1999), using the expression k=AT 2 e −B/T , leads to k(cyclopentane)=2.64×10 −17 T 2 e (219±21)/T cm 3 molecule −1 s −1 over the temperature range 270-1200 K, where the indicated uncertainty in the value of B is two least-squares standard deviations, and k(cyclopentane)=4. 298 K (i.e.…”

“…As shown in Table 54, rate constants for cyclopentane-d 10 are available only from the absolute rate study of Droege and Tully (1987 (1988) ratios k H /k D (CH 2 /CD 2 groups) obtained by Droege and Tully (1986a) for the propane reactions (k H /k D (CH 2 /CD 2 groups)=(1.13±0.19)e (262±78)/T over the temperature range 295-854 K, k H /k D (CH 2 /CD 2 groups)=2.62±0.49 at 295 K), by Droege and Tully (1986b) for the n-butane reactions (k H /k D (CH 2 /CD 2 groups)=(1.31±0.12)e (196±33)/T over the temperature range 294-509 K, k H /k D (CH 2 /CD 2 groups)=2.52±0.17 at 294 K) and by Droege and Tully (1987) for the cyclohexane reactions (k H /k D (CH 2 /CD 2 groups)=(1.16±0.06)e (237±10)/T over the temperature range 292-491 K, k H /k D (CH 2 /CD 2 groups)=2.59±0.16 at 292 K).…”