1H and 13C NMR chemical shifts of methyl-substituted benz[ a]anthracenes

Abstract

High-resolution 1H NMR spectra are described for 1-, 2-, 3-, 4-, 5-, 6-, 8-, 11-, and 12-methyl-and 1,12-, 3,9-, and 3,10-dimethylbenz[ a]anthracenes recorded at 220 MHz in carbon disulphide solution. 1H shifts reflect ortho and para substituent effects as well as molecular distortions, especially in the bay regions of the 1-, 12-, and 1,12- compounds. 13C NMR resonances are reported for 4-,5-, and 12-methyl-, and 1,12-, 3,9-, and 3,10-dimethylbenz[ a]lanthracenes. The protonated aromatic 13C shifts show γ- and δ-steric effects; γ shieldings also cause higher field (20 ppm) CH 3-resonances in 4- and 5-methylbenz[ a]anthracenes than for unhindered methyl groups (∼ 21.6 ppm) in 3,9- and 3,10-dimethylbenz[ a]anthracenes.