Experimental and computational study of the kinetics of OH plus pyridine and its methyl- and ethyl-substituted derivatives

The overall rate constants for the reaction of OH with pyridine, its three monosubstituted methyl derivative isomers (the picolines), its six disubstituted methyl derivative isomers (the lutidines), and its three monosubstituted ethyl derivative isomers have been measured using the turbulent flow technique with high-pressure chemical ionization mass spectrometry at 100 Torr pressure and 298 K. A structure-reactivity relationship model for parametrizing the OH rate constants based on the type and position of the methyl and ethyl substituents on the pyridine ring has been constructed, and similar accuracy to that previously obtained for benzene derivative rate data is achieved. Transition state theory calculations have been performed to explore the substituent effect on the observed OH rate constants. The atmospheric implications of the findings are discussed in terms of the role of pyridinated compounds in the ionic composition of the troposphere.