Predicting arene rate coe ffi cients with respect to hydroxyl and other free radicals in the gas-phase : a simple and e ff ective method using a single
Predicting arene rate coefficients with respect to hydroxyl and other free radicals in the gas-phase: a simple and effective method using a single topological descriptor M. R. McGillen, C. J. Percival, G. Pieterse, L. A. Watson, and D. E. Shallcross School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, The Sackville Building, Sackville Street, P.O. Box 88, Manchester M60 1QD, UK Department of Air Quality and Climate Change, Energy Research Centre for the Netherlands, P.O. Box 1, 1755 ZG Petten, The Netherlands Biogeochemistry Research Centre, School of Chemistry, The University of Bristol, Cantock’s Close BS8 1TS, UK Received: 13 November 2006 – Accepted: 2 February 2007 – Published: 26 February 2007 Correspondence to: C. J. Percival (c.percival@manchster.ac.uk)
Kinetics and mechanism of reactions between aromatic olefins and hydroxyl radicals
The rates of the reactions of hydroxyl radicals (OH) with styrene, α-methylstyrene, and β-methylstyrene have been measured by irradiating mixtures of these aromatic olefins and NO in an environmental chamber at 298 K. Experimental conditions were used whereby the competition of ozone with OH in oxidizing the hydrocarbons could be considered negligible. The rate constant values, obtained by a relative method using isooctane as reference hydrocarbon, are: styrene (5.3 ± 0.5) × 10−11 cm3/molec·s, α-methylstyrene (5.3 ± 0.6) × 10−11 cm3/molec·s, and β-methylstyrene (6.0 ± 0.6) × 10−11 cm3/molec·s. A simplified kinetic treatment of the experimental data shows that styrene and β-methylstyrene are stoichiometrically converted to benzaldehyde, suggesting that OH attack occurs only on the aliphatic moiety of the aromatic olefins. Benzaldehyde was observed to undergo consecutive oxidation by OH, and its maximum formation yield was about 60%. A reaction mechanism is proposed where the primary rate-determining OH attack leads to the formation of 1-hydroxy-2-phenyl-2-ethenyl radicals, from which benzaldehyde is formed through fast intermediate reactions.
The Variable Molecular Descriptors Based on Distance Related Matrices
Recently variable molecular connectivity index and variable paths have been tested as molecular descriptors in several structure-property regressions. Here we outline the construction of several variable molecular descriptors, derived from the distance matrix and the "reversed" distance matrix. This includes the variable Balaban J index and the "reversed" Balaban index 1/J as well as a novel index 1/JJ derived from J and 1/J. All the variable descriptors mentioned were constructed by augmenting the distance matrix by replacing the diagonal zeroes with the variables x, y, z,.