Is it possible to use the 31P chemical shifts of phosphines to measure hydrogen bond acidities (HBA)? A comparative study with the use of the 15N chemical shifts of amines for measuring HBA

Abstract

The geometries, energies, and nuclear magnetic resonance (NMR) chemical shifts of 3 bases (trimethylphosphine, trimethylamine, and trimethylphosphine oxide), their 3 protonated cations, and 15 hydrogen-bonded complexes (corresponding to the HF, HNC, HCN, HCCH, HO, and CHOH Brønsted acids) have been calculated at the B3LYP/6-311++G(d,p) level. The determination of hydrogen bond acidities by NMR is classically performed using the P chemical shifts MePO. This method is more reliable than the use of the N NMR chemical shifts of MeN. This work shows that the P NMR chemical shifts of MeP cannot be used. The raison of the difference between MeP on one hand and MePO and MeN on the other will be discussed.