NMR properties (chemical shift and relaxation rate) of acceptor and hydrogen bridge nuclei in hydrogen-bonded complexes

The NMR properties related to the formation of hydrogen bonds (HB) between phenol or N-methyltrifluoroacetamide and several acceptors (amines, carbonyl compounds, nitriles, amides) in CCl4 or CHCl3 were investigated through the analysis of NMR chemical shifts and relaxation times of the deuteron bridge (H-2), and the chemical shifts of the heteronuclei (N-14 and O-17) directly involved in the HB interaction. Thus, a comparison is made between such delta or T-1 values and nuclear shieldings or electric field gradients calculated by ab initio and DFT methods for the acceptor molecules, both isolated and in 1:1 or 2:1 H-bonded complexes. The H-2 relaxation rates undergo small changes, essentially insensitive to the nature of the acceptor. On the other hand, good relationships are found to hold between calculated and experimental chemical shift changes, both for H-2 and for the acceptor nuclei.