Temperature dependence of cyanogen radical reactions with selected alkanes: CN reactivities towards primary, secondary and tertiary CH bonds

David L. Yang, Tao Yu, Niann-Shiah Wang, Ming-Chang Lin*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Scopus citations

Abstract

The absolute rate constants for the reactions of CN with C2H6, C3H8, i-C4H10, neo-C5H12 (neopentane), and C8H18 (hexamethylethane, HME) have been measured between 170 and 740 K using the laser photolysis/laser-induced fluorescence method. These rate constants, expressed in units of cm3/s can be effectively represented by kC2H6 = 1.04 × 10-14 T1.26exp (208/T), kC3H8 = 2.44 × 10-14T1.19exp(378/T), ki-C4H10 = 3.61 × 10-14T1.16exp(392/T), kneo-C5H12 = 1.28 × 10-12T0.61exp(230/T), and kHME = 10(-9.97±0.05)exp(47±15/T). Based on the averaged value of the primary CH rates in ethane and neopantane, we estimate the rate constant for the CN attack on tertiary CH in i-C4H10 to be kt(i-C4H10) = 6.86 × 10-17 T1.89exp(720/T) and the rate for the CN attack on each secondary CH in C3H8 to be kS (C3H8) = 6.25 × 10-15T1.17exp(440/T) A negative temperature dependence of the rate is observed in the low-temperature studies with propane and isobutane which is attributed to steric hindrance of the more reactive secondary and tertiary CH bonds by the less reactive CH3 groups. The lack of a significant negative temperature dependence for CN+ neopentane and HME lends support to this model.

Original languageAmerican English
Pages (from-to)307-315
Number of pages9
JournalChemical Physics
Volume160
Issue number2
DOIs
StatePublished - 1 Mar 1992

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