Substituent effects in C6H5X center dot center dot center dot M+ (M+ = Li+, Na+, K+, and NH4+) systems have been characterized using isotropic nuclear magnetic shielding constants (sigma). Good linear relationship between sigma and the Hammett substituent constant sigma(p) is established which suggests that the substituent effects can be quantified by NMR experiments. Irrespective of the electronic nature of X, meta carbons, and all the hydrogens are always deshielded and this property is useful for detecting cation-pi interaction. The sigma-scan plots revealed that the deshielding effect of the cation on the aromatic ring is significant even at large cation-pi distance (similar to 4.5 angstrom). (C) 2011 Elsevier B.V. All rights reserved.