The relationship between partial bond fixation induced by through-bond and/or through-space perturbations in nonplanar benzene derivatives and proton spin-spin coupling constants

4 J Me-C-C-H = 4 J OB , the spin-spin coupling constant over four formal bonds between methyl protons and a proton bonded to an sp carbon, previously established 9-17 was a probe for bond order, was determined for 6-methyl-1,4-dihydro-1,4-methanonaphthalene (1) and for a number of reference compounds 2-5. Self-consistent field (SCF) calculations at the 3-21G level for 1-4 predict partial bond fixation in the benzene ring for all molecules in the sense predicted by interpretation of previously-reported photoelectron spectra of closely-related molecules