A structure-activity relationship for the estimation of rate constants for the gas-phase reactions of OH radicals with organic compounds

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Abstract

A previous technique for the calculation of rate constants for the gas-phase reactions of the OH radical with organic compounds has been updated and extended to include sulfur- and nitrogen-containing compounds. The overall OH radical reaction rate constants are separated into individual processes involving (a) H-atom abstraction from C[BOND]H and O[BOND]H bonds in saturated organics, (b) OH radical addition to >C[DOUBLE BOND]C< and [BOND]C[TRIPLE BOND]C[BOND] unsaturated bonds, (c) OH radical addition to aromatic rings, and (d) OH radical interaction with [BOND]NH2, >NH, >N[BOND], [BOND]SH, and [BOND]S[BOND] groups. During its development, this estimation technique has been tested against the available database, and only for 18 out of a total of ca. 300 organic compounds do the calculated and experimental room temperature rate constants disagree by more than a factor of 2. This suggests that this technique has utility in estimating OH radical reaction rate constants at room temperature and atmospheric pressure of air, and hence atmospheric lifetimes due to OH radical reaction, for organic compounds for which experimental data are not available. In addition, OH radical reaction rate constants can be estimated over the temperature range ca. 250–1000 K for those organic compounds which react via H-atom abstraction from C[BOND]H and O[BOND]H bonds, and over the temperature range ca. 250–500 K for compounds containing >C[DOUBLE BOND]C< bond systems.

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