Rates of OH radical reactions. XII. The reactions of OH with cC₃H₆, cC₅H₁₀, and cC₇H₁₄. Correlation of hydroxyl rate constants with bond dissociation energies

Abstract

Absolute rate constants for H-atom abstraction by OH radicals from cyclopropane, cyclopentane, and cycloheptane have been determined in the gas phase a t 298 K. Hydroxyl radicals were generated by flash photolysis of H,O vapor in the vacuum UV, and monitored by time-resolved resonance absorption a t 308.2 nm [OH(AL87+X'nl. The rate constants in units of cm3 mol-' s a t the 955% confidence limits were as follows: k(c-C3H,) = (3.74 -+ 0.83) x lo'', k(c-C5Hlo) = (3.12 5 0.23) x lo", k(c-C,H,,) = (7.88 5 1.38) x 10". A linear correlation was found to exist between the logarithm of the rate constant per C-H bond and the corresponding bond dissociation energy for several classes of organic compounds with equivalent C-H bonds. The correlation favors a value of D(c-C3H, -H) = (101 -+ 2) kcal mol-'.

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

“…While this discrepancy could be due to the presence of reactive impurities in the cyclopropane sample used by Dóbé et al (1991Dóbé et al ( , 1992, Dóbé et al (1991Dóbé et al ( , 1992 stated that the cyclopropane sample was ≥99.99% pure with 0.01% propene impurity (Dóbé et al, 1992) (which would result in a ∼4% increase in the measured rate constant at 298 K). The room temperature rate constants of Jolly et al (1985), Clarke et al (1998), DeMore and Bayes (1999) and Wilson et al (2001) are in good agreement. However, as evident from the Arrhenius plot (Fig.…”

“…18). Obviously, further data are needed at temperatures <290 K to better assess the temperature dependence of the rate constant in the range 200-300 K. The significantly different temperature dependencies obtained by Clarke et al (1998) and by DeMore and Bayes (1999) and Wilson et al (2001) lead to the recommended rate expression giving an ∼10% higher calculated 298 K rate constant than measured by Jolly et al (1985), Clarke et al (1998), DeMore and Bayes (1999) and Wilson et al (2001).…”

“…Rate constants are available from the absolute rate studies of Jolly et al (1985), Dóbé et al (1991Dóbé et al ( , 1992 and Clarke et al (1998) and from the relative rate studies of DeMore and Bayes (1999) and Wilson et al (2001). Figure 18 shows an Arrhenius plot of the data from these studies (for the study of Wilson et al (2001) only the data obtained relative to the rate constant for ethane are plotted).…”

“…A least-squares analysis of the rate constant data of Jolly et al (1985), Clarke et al (1998), DeMore and Bayes (1999) and Wilson et al (2001) (relative to ethane; while the rate constants obtained by Wilson et al (2001) relative to ethane agree with those obtained relative to CH 3 CHF 2 (to within ∼±10%), due to the larger uncertainty in the rate constant for the reaction of OH radicals with CH 3 CHF 2 only the rate constants relative to ethane are used in the evaluation), using the expression k=AT 2 e −B/T , leads to the recommendation of k(cyclopropane)= 4.21×10 −18 T 2 e −(454±87)/T cm 3 molecule −1 s −1 over the temperature range 200-460 K, where the indicated uncertainty in the value of B is two least-squares standard deviations, and k(cyclopropane)=8.15×10 −14 cm 3 molecule −1 s −1 at 298 K, with an estimated uncertainty at 298 K of +10%, −30%. This recommended expression is shown in the Arrhenius plot as the solid line (Fig.…”

“…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.…”