A large number of para-substituted benzene thiols and the corresponding disulfides were synthesized and characterized by 1H NMR, 13C NMR, and IR spectroscopies. Geometries of all sixteen thiols and fourteen disulfide compounds were optimized at the B3LYP/6-31G(d) level, while the electronic structure and the 13C isotropic shifts were calculated by ab initio Hartree-Fock method coupled with the Gauge-Independent Atomic Orbital (GIAO) algorithm and a 6-31+G(d,p) basis set. The calculated 13C NMR isotropic shifts exhibit admirable agreement (δ rmsd ∼4.6 ppm) with the experimental data. The chemical shift of para-substituted carbon showed a linear correlation with Hammett constants (σp and σp+). Using this methodology the σp+ constants for the dendritic ligands have been estimated to be 0.25 and 0.24 for 2(n) and 2(o), respectively. In addition, the NBO charges on the sulfur atoms shows a latent response with the σp+ parameter. The atomic charge on the thiophenolato sulfur is invariant with the electron withdrawing ability of the substituents, however, the charge increases with increasing electron-withdrawing power.
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