Ring currents are thought to be responsible for unusual magnetic susce
ptibility effects in organic ring systems and represent a method of me
asuring cyclic stabilization/destabilization (aromaticity/antiaromatic
ity). They should, in principle, also affect nuclear shieldings in suc
h systems, especially proton shieldings. By studying a variety of four
-, five-, and six-membered organic ring systems, we investigate the qu
estion here by theoretical means as to whether proton shieldings refle
ct such cyclic stabilization/destabilization effects as measured by ho
momolecular homodesmotic reaction energies. While absolute shieldings
show only a slight hint of correlation, it is found that differences i
n ring proton shieldings between the fully unsaturated species and its
monoene counterpart show a clear correlation with this energy. In par
ticular, mean differential shieldings exhibit a good linear relationsh
ip with the homomolecular homodesmotic reaction energy that is quantit
atively comparable to other measures of aromaticity/antiaromaticity. (
C)1998 Elsevier Science B.V. All rights reserved.