부산대학교 도서관

A high-levelquantum chemistry investigation has been carried outfor the addition and abstraction reactions by the radicals •OH and •OOH to and from the model alkenes 3-methylpyrroleand benzene. These models were chosen to reflect the functionalitiescontained in the side chain of the amino acid tryptophan. The W1BDprocedure was used to calculate benchmark barriers and reaction energiesfor the smaller model system of •OOH addition toethylene. It was found that the CBS-QB3 methodology compares bestwith the W1BD benchmark, demonstrating a mean absolute deviation (MAD)from W1BD of 3.9 kJ mol–1. For the reactions involvingthe •OH radical and benzene or 3-methylpyrrole,addition is favored over abstraction in all cases. In particular theCBS-QB3 calculations suggest a barrierless addition reaction of the •OH radical to position two of 3-methylpyrrole. Forthe analogous addition and abstraction reactions involving the •OOH radical, the same order of reactivity was found,albeit with higher barriers. A number of other processes involvingthe addition of the •OOH radical were also investigated.The main findings of these studies determined that the initial •OOH barrier of stepwise addition to 3-methylpyrrole(+18.8 kJ mol–1) is significantly smaller than theconcerted addition barrier (+71.5 kJ mol–1). Thisconclusion contrasts starkly with the situation for ethylene in whichit is well established that the concerted process has the smallerbarrier. A considerable variety of contemporary density functionaltheory procedures have been tested to examine their accuracy in predictingthe CBS-QB3 results. It was found that the best overall performingmethod was UBMK with an MAD of 7.3 kJ mol–1. A numberof other functionals additionally performed well. They included UM06,RM06, UXYG3 and RXYG3, all of which have MADs of less than 8 kJ mol–1. [ABSTRACT FROM AUTHOR]