High-Resolution NMR Spectra of Polycyclic Hydrocarbons. II. Pentacyclic Compounds

The McWeeny theory has been used to calculate chemical shielding parameters for all even, alternant, pentacyclic hydrocarbons, and comparison with experiment was made where data were available. The spectra of two pentacyclic molecules, 1,2,3,4-dibenzanthracene and picene, not reported previously, were obtained and analyzed, and a complete analysis of the 1,2-benzpyrene spectrum is given. Agreement between theory and experiment is satisfactory for protons not subject to large van der Waals contact, and it is found that steric effects contribute an extra downfield shift of 0.54 ppm to angular phenanthrenic type protons. Additions and new interpretations are made for previously reported results of similar data on three- and four-ring molecules.