A comparative study of the aromatic character of furan, thiophen, selenophen, and tellurophen
The ground state aromaticities of furan, thiophen, selenophen, and telurophen have been compared using seven different criteria: the n.m.r. dilution shift, the difference in chemical shifts of the β- and α-protons, the effect of a 2-methyl substituent on the ring proton chemical shifts, the diamagnetic susceptibility exaltation, the sum of the bond orders, the Julg parameter, and the mesomeric dipole moment. The agreement among the results obtained using the various approaches is remarkably good. The following order of decreasing aromaticity has been establised: benzene > thiophen > selenophen > tellurophen > furan.