Theoretical study on rotational barriers of 1,3‐dipoles and mechanisms of 1,3‐dipolar reactions

Abstract

SUMMARYThe different orbitals for different spins molecular orbital and complete active space (CAS) SCF MO descriptions of azomethyne ylides, carbonyl ylides and related oxygenated dipoles were performed as a continuation of earlier papers. Rotational energy barriers for the C-C double bond of ethylene at the equilibrium and dissociated geometries, and the 1,3-dipolar species were calculated by UHF, APUHF, UMP, APUMPn, CASSCF and CASSCF MP2 procedures, and were discussed in relation to their biradical characters and stereospecificity of 1,3-dipolar reactions. It was found that the biradical characters of carbonyl ylides and related species are quenched by the symmetry-allowed orbital interactions with olefins, in accord with the symmetry-allowed concerted property. The rotational energy barriers for 1,5 biradicals were also examined in relation to the non-concerted mechanism of 1,3-dipolar reactions. The implications of these results are discussed in relation to the concerted and biradical mechanisms of 1,3-dipolar additions such as ozonolysis reactions.

Theoretical study on electronic structures of FeOO, FeOOH, FeO(H2O), and FeO in hemes: As intermediate models of dioxygen reduction in cytochrome c oxidase

“…The shapes of SOMO À 1 and SOMO + 1 are perfectly same as those of the B1 state, in harmony with that the electron occupations, 1.328e and 0.672e, for the SOMO À 1 and SOMO + 1 of the C2 state are same as 1.317e and 0.683e for the B1 state, respectively, as can be found from Table 4. The biradical character of the C2 state is estimated to be 0.408 from the electron occupations [35,[38][39][40], showing the weak antiferromagnetic spin coupling. It can be seen that the SOMO is a p * orbital of the porphyring ring and has the b 3g symmetry of the D 2h point group.…”

“…The charge and spin distributions are estimated by the natural bond analysis [36,37]. For the energy, the spin contaminations of the next higher sates could be approximately removed for the open state with the spin multiplicity of 2S + 1, as follows [38][39][40]:…”

A computational study of the 1,3-dipolar cycloaddition reaction mechanism for nitrilimines

“…Interaction energies (∆E, eV) between the "frontier" molecular orbitals of nitrilimine and ethene (lowest interaction energies are in boldface type). majority of 1,3-dipolar cycloaddition reactions are believed to proceed via a concerted mechanism (23), although there are now several reports of reactions with a biradical mechanism (1,(61)(62)(63)(64)(65).…”

Applications of B3LYP Method for Enzyme Reactions: O[sub 2] Reduction by Cytochrome c Oxidase and Ubiquinol Oxidation by Cytochrome bc[sub 1] Complex

“…Then, the energetics is discussed based on the energy obtained by the broken symmetry. However, in the case of single antiferromagnetic spin couphng such as CcO, the spin contamination from next higher spin state was approximately removed [40][41][42].…”