Fig. 3.

a DFT-based normalized chemical shifts for three CF₃ tags conjugated to methanethiol (shown in c). Isotropic NMR shifts for each of the tags were calculated using the B3LYP hybrid functional and the 6-31G(d,p) basis set, under six different solvent conditions and one vapor phase [left to right: vapor phase (Py = 0.4), toluene (Py = 1.04), ethanol (Py = 1.18), methylene chloride (Py = 1.35), acetone (Py = 1.64), water (Py = 1.87), and dimethyl sulfoxide (Py = 1.95)]. b DFT-based normalized average partial charges for ¹⁹F atoms for each of the above three CF₃ tags, as a function of solvent polarity. The partial charges for each of the ¹⁹F atoms in the CF₃ group were averaged assuming isotropic conditions and fast methyl rotations and then normalized to the average ¹⁹F partial charge for the conjugate in H₂O. Dotted lines indicate the polarity region assessed experimentally by NMR via MeOH/H₂O solvent mixtures (Fig. 2). c Structure of the three methanethiol conjugates for which DFT calculations were performed