Solvent effects on the electronic state of monolignol radicals as predicted by molecular orbital calculations

Abstract

The spin and charge densities in three monolignol radicals were computed using the UB3LYP/6-31G*method of molecular orbital calculation. As well, the effects of solvents were simulated by using an SCI-PCM model. It was confirmed that an unpaired electron was localized at C1, C 3, C5, C8, and O4 for all monolignol radicals. In solvents, the spin density decreased at O4 with increasing solvent polarity, but increased at C8. The atomic charges at all reactive atoms had a negative value and were obviously strengthened at O4 with increasing solvent polarity. These tendencies support the experimental results for radical coupling reactions of monolignols in various solvents; that is, that 8-O4′ linkages are produced much more often than 8-8′ linkages in nonpolar solvents. © 2008 The Japan Wood Research Society.