13C Nuclear Magnetic Resonance Studies of Methylated Anthracenes

Abstract

The 13C n.m.r. spectra of anthracene and 11 methylated anthracenes have been examined. Analysis of the 1H spectra allowed unequivocal assignments for most of the protonated carbons by selective proton decoupling. Parameters describing the methyl substituent effects on the aryl carbon shieldings were defined and refined by regression analysis so that the 13C shieldings were predicted for 67 independent aryl positions in anthracenes without peri-methyls with a standard deviation of 0.12 p.p.m. Peri methyl-methyl interactions cause considerable deviations from the predicted substituent effects. The relationships of the 13C shieldings to charge densities calculated by the CNDO/2 method were briefly examined. Syntheses of 2,7,9-trimethyl-, 1,4,5,8- and 1,4,5,9-tetramethyl-, and 1,4,5,8,9-pentamethylanthracene are described.