Isobutylene, peroxyformic acid epoxidation

The numbers in brackets for propylene, isobutylene, iJ-2-butene and 1,3-butadiene entries are at the QCISD(T)//QCISD/6-31G(d) level of theory QCISD(T)/6-31G(d)//B3LYP/6-311- -G(3df,2p) gas-phase intrinsic barriers (AE ) for the epoxidation of -2-butene with dimethyldioxirane (DMDO) and peroxyformic acid are 14.3 and 13.2 kcalmol respectively. 

FIGURE 22. Selected geometrical parameters of the transition stmcture for the epoxidation of isobutylene with peroxyformic acid calculated at the QCISD/6-31G, CISD/6-31G (in parentheses), B3LYP/6-31G (in square brackets), B3LYP/6-311+G(3df,2p) (in italic in square brackets) and MP2/6-31G (in curly brackets) levels... 

The epoxidations of propylene and isobutylene with peroxyformic acid proceed in a concerted way via slightly unsymmetrical Markovnikov-type transition stmctnres where the differences in the bond distances between the donble-bond carbons and the spiro oxygen are only 0.021 and 0.044 A at the QCISD/6-31G level. In contrast, the more polarizable natnre of the carbon-carbon double bond of o ,/ -unsaturated systems results in a highly nnsymmetrical transition structure for the epoxidation of 1,3-butadiene with an order-of-magnitnde difference in the carbon-oxygen bond distances of 0.305 A at the QCISD/6-31G level. A highly unsymmetrical transition structure has been also found for the epoxidation of acrylonitrile. 

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