COMPUTATIONAL STUDY ON NATURE OF TRANSITION STRUCTURE FOR OXYGEN-TRANSFER FROM DIOXIRANE AND CARBONYLOXIDE

The relative reactivity of a series of nucleophiles that includes ethy lene, sulfides, sulfoxides, amines, and phosphines toward dioxirane, d imethyldioxirane, carbonyloxide and dimethylcarbonyloxide has been exa mined at the MP4/6-31G//MP2/6-31G*, QCISD(T)/6-31G*//MP2/6-31G*, and B3-LYP/6-31G levels of theory. The barriers for the oxidations with d imethyldioxirane are higher (up to 2.5 kcal/mol for the oxidation of H 2S) than those for the oxidations with the parent dioxirane. The oxida tion barriers for dioxirane are larger than those for the oxidations w ith peroxyformic acid, except the barriers for the oxidation of sulfox ides. The reactivity of dimethylsulfide toward dimethyldioxirane was f ound to be comparable to that of dimethylsulfoxide both in the gas pha se and in solution (chloroform). The classical gas phase barrier for t he oxidation of trimethylamine to trimethylamine oxide was higher (6.3 kcal/mol at the MP4//MP2/6-31G level) than that for oxygen atom tran sfer to trimethylphosphine. When the transition states were examined b y self-consistent reaction field (SCRF) methods, the predicted barrier s for the oxidation of amines and phosphines were found to be in good agreement with experiment. The general trend in reactivity for oxidati on by dioxirane was R2S approximate to R2SO, R3P > R3N in the gas phas e, and R2S approximate to R2SO, R3N approximate to R3P (R = Me) in sol ution. The oxidation barriers calculated using the B3-LYP functional w ere lower than those computed at the MP4 and QCISD(T) levels. (C) 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1353-1369, 1998.