Solvent-induced chemical shifts in sterically hindered polynuclear aromatic hydrocarbons

Abstract

Differential ¹H n.m.r. chemical-shifts induced by six solvents are correlated for the hydrocarbons phenanthrene, benzo[c]phenanthrene, dibenzo[c,g]phenanthrene, 4-methylphenanthrene, and 9-methylphenanthrene. Relative to the shifts in cyclohexane, shifts for other solvents are very similar for non-sterically-hindered hydrogens. The solvent-induced chemical shifts of the ‘bay’ hydrogens are progressively decreased, relative to those of the ‘perimeter’ hydrogens, by increase of steric hindrance at the latter sites. The shifts induced by [²H₆] benzene are in opposite directions to those of the other solvents, carbon disulphide, [²H]chloroform, and acetone.