The site of protonation of several types of amide bases (carboxylic amides and thioamides, sulfenamides, sulfinamides, sulfonamides, nitrosamides, nitramides, cyanamides, and phosphorous and phosphoric acid triamides) has been investigated through a combination of quantum chemical calculations and heteronuclear NMR measurements. Relative energies of tautomeric ions deriving from protonation at the various sites were determined both in the gas phase (by MP2 calculations) and in water (by the IPCM continuum solvation method). Relevant NMR properties of the involved heteronuclei (nuclear shielding and electric field gradient) were calculated at the GIAO-HF level, and compared with chemical shifts and relaxation rates experimentally measured in 14 N, 17 O, and 31 P spectra. It is shown that such a combination of theoretical and experimental tools allows a dependable prediction of spectral parameters and ultimately of the protonation site of amides. The reliability of common assumptions, like the comparison of spectral parameters of polyfunctional bases and monofunctional models, is also scrutinized and tested.

Mid-infrared vibrational unpolarised absorption and vibrational circular dichroism (VCD) spectra of CCl4 solutions of tert-butyl methyl sulfoxide (1) are reported. The spectra are compared to ab initio density functional theory (DFT) calculations carried out using two functionals, B3PW91 and B3LYP, and two basis sets, 6-31G* and TZ2P. The VCD spectra are calculated using Gauge-invariant atomic orbitals (GIAOs). The analysis of the VCD spectrum confirms the R(-)/S(+) absolute configuration of 1. The advantages and disadvantages of VCD spectroscopy in determining the absolute configurations of chiral sulfoxides are discussed.

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