Paramagnetic ring currents in the carbanion of 5H-dibenzo [a,d] cycloheptene and the nitranion of 5H-dibenz[b,f] azepine

The proton NMR spectra of the carbanion of 5H-dibenzo[a, d] cycloheptene (DbcH^?) and the nitranion of 5H-dibenz[b, f] azepine (Dba?) have been recorded and interpreted. Numerical values for the ring current in each ring have been estimated by a least squares analysis of the observed chemical shifts, after applying corrections for the excess charges and local electric dipoles. The results point to a strong paramagnetic ring current in the seven-membered ring, the one in DbcH? being larger than in Dba?.