The use of transition‐state theory to extrapolate rate coefficients for reactions of oh with alkanes

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A method is described for extrapolating existing experimental data on the reactions of OH radicals with alkanes to higher temperatures using conventional transition‐state theory. Expressions are developed for the estimation of the structural properties of the activated complex necessary for calculating Δ S ± and Δ H ± . The vibrational frequencies and internal rotations of the activated complex are given by those of the reacting alkane or the analogous alcohol and a set of additional internal modes that is the same for all OH + alkane reactions considered. Differences between primary, secondary, and tertiary hydrogen attack are discussed, and the validity of representing the activated complexes of all OH + alkane reactions by a fixed set of vibrational frequencies and other internal modes is evaluated. Calculations are presented for the reaction of OH with CH 4 , C 2 H 6 , C 3 H 8 , n ‐C 4 H 10 , i ‐C 4 H 10 , c ‐C 4 H 8 , c ‐C 5 H 10 , c ‐C 6 H 12 , (CH 3 ) 2 CHCH(CH 3 ) 2 , (CH 3 ) 3 CCH(CH 3 ) 2 , (CH 3 ) 4 C, and (CH 3 ) 3 CC(CH 3 ) 3 , and the results are compared with experiments.