THE S-0 AND S-1 METHYL-GROUP TORSIONAL BARRIERS IN 2-METHYL-1-NAPHTHOL DEPEND UPON THE ORIENTATION OF THE OH GROUP

The two OH rotamers of 2-methyl-1-naphthol, syn-2M1HN and anti-2M1HN, have different CH3 torsional barriers in both their ground and first e xcited electronic states, as revealed by high-resolution laser studies of their S1<--S0 fluorescence excitation spectra in a molecular beam. A comparison of the measured barriers with the results of ab initio c alculations suggests that a primary factor responsible for these diffe rences is a difference in the magnitudes of the repulsive steric inter actions of the hydrogen and oxygen atoms of the OH group with the ecli psed hydrogen of the CH3 group.