Magnetic circular dichroism studies. Part 55. The aliphatic nitro chromophore

Abstract

The magnetic circular dichroism (m.c.d.) of twelve nitroalkanes is reported. For several of these compounds two distinct m.c.d. bands are observed in the 240–350 nm region. The presence of these bands is interpreted in terms of two electronic transitions, viz. a σ→π* transition at ca. 320 nm and an n→π* transition at ca. 270–280 nm. The magneto-optical B values for the σ→π* transition appear to be small in magnitude throughout the series of compounds; the B values for the n→π* transition are generally much larger in magnitude and are sensitive to alkyl substitution and to solvent effects. A qualitative interpretation of the spectra is given in terms of the effects of static and structural–vibrational perturbations on the m.c.d. associated with symmetry-forbidden transitions. Solvent effects observed in the m.c.d. spectra of the nitroalkanes are also discussed.