Electronic properties of para-substituted thiophenols and disulfides from 13C NMR spectroscopy and ab initio calculations: relations to the Hammett parameters and atomic chargesElectronic supplementary information (ESI) available: all characterization data are tabulated in Table S1. A figure showing the dependence of the natural charge of the C1 atom of the disulfides on the 13C NMR chemical shift is also provided. See http://www.rsc.org/suppdata/nj/b3/b300048f/