Effect of double-bond substituents on the rate of cyclization of α-carbomethoxyhex-5-enyl radicals.

Rate constants have been calculated, and compared with experimental results, for the cyclizations of 1-carbomethoxy-1-methyl-5-hexenyl radicals (2) with various substituents on C6. The calculations have been done by DFT at the B3LYP/6-311++G** level of theory. They show considerable interaction between C5 and the radical centers even in the ground state of all of the radicals 2.

Carbon-cobalt bond distance and bond cleavage in one-electron reduced methylcobalamin: a failure of the conventional DFT method.

Geometry optimizations at the HF, B3LYP, and CASSCF levels of electronic structure theory have been performed for methylcobalamin (MeCbl) model compounds in both the Co(III) (MeCbl(III)) and Co(II) (MeCbl(II)) formal oxidation states. Since the HOMO-LUMO and C-Co sigma-sigma MO gaps are significantly smaller in the MeCbl(II) compounds compared with MeCbl(III), a pseudo-Jahn Teller effect is possible. CASSCF calculations show that there is strong coupling between C-Co sigma-sigma MOs for the MeCbl(II) models leading to strong state mixing with significant total charge density transfer (approximately 0.

Electroreduction of a series of alkylcobalamins: mechanism of stepwise reductive cleavage of the Co-C bond.

The electrochemical (EC) reduction mechanism of methylcobalamin (Me-Cbl) in a mixed DMF/MeOH solvent in 0.2 M tetrabutylammonium fluoroborate electrolyte was studied as a function of temperature and solvent ratio vs a nonaqueous Ag/AgCl/Cl(-) reference electrode. Double-potential-step chronoamperometry allowed the rate constant of the subsequent homogeneous reaction to be measured over the temperature range from 0 to -80 degrees C in 40:60 and 50:50 DMF:MeOH ratios.