NUCLEAR MAGNETIC RESONANCE EFFECTS IN SYSTEMS WITH STERICALLY INTERFERING PROTONS

Author Institution: Department of Chemistry, The University of British ColumbiaThe nuclear magnetic resonance spectra of about 40 polynuclear aromatic hydrocarbons have been examined. It has been found that the largest chemical shifts are due to direct proton-proton interference between suitably placed neighbours. These may be in identical or non-identical environments and are consequently not electron coupled spin-spin effects, but ""repulsive"" chemical shifts. Using ring systems of different shapes and sizes, a correlation between proton-proton distance and shifts has been found. Some new ideas about steric hindrance are suggested