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

Semi-empirical calculations of chemical shifts in partially paratropic anions

“…The ring-current model implies that in polycyclic systems the total electronic motions should break down into currents flowing around each individual ring. Several authors have considered the feasibility of such a breakdown, both from a theoretical [7,12,14,21,22] and from an experimental [2,3] …”

“…The chemical shifts are presented in table 1. The large differences between shifts of corresponding protons have been attributed to ring-current effects ; in the series TxH-, XH-, Dba-and DbcH-an increasing paramagnetic ring current in the central ring has been postulated [2,3]. In this paper a theoretical study of the proton chemical shifts of the anions is given.…”

“…Other contributions to a n are ignored, e.g. those arising from the magnetic anisotropies and lone-pair dipoles of the heteroatoms ; these effects are small, as can be inferred from calculations [2,3] and from the variation of (a 1-a,). It is assumed furthermore that the shifts of F1H-in 1,2-dimethoxyethane (DME) are comparable with those of the other systems in liquid NHa, Downloaded by [University of California, San Diego] at 12:48 29 June 2016 (The numbering of DbcH-and Dba-is not standard, and also differs from that used in reference [3]).…”

“…It is assumed furthermore that the shifts of F1H-in 1,2-dimethoxyethane (DME) are comparable with those of the other systems in liquid NHa, Downloaded by [University of California, San Diego] at 12:48 29 June 2016 (The numbering of DbcH-and Dba-is not standard, and also differs from that used in reference [3]). [3] i.e. that the solvent effect is small; for AH-, the N.M.R.…”

“…spectra of a series of tricyclic conjugated anions have been published [1][2][3], i.e. of the conjugate bases of fluorene (F1H2) , 9,10-dihydroanthracene (AH~), xanthene (XH2) , thioxanthene (TxH~), dibenzo-[a,d]cycloheptene (DbcH2) and dibenz[b,f]azepine (iminostilbene, DbaH) (figure 1).…”