The exact knowledge of hydrogen atomic positions of O-H···O hydrogen bonds in solution and in the solid state has been a major challenge in structural and physical organic chemistry. The objective of this review article is to summarize recent developments in the refinement of labile hydrogen positions with the use of: (i) density functional theory (DFT) calculations after a structure has been d...

The history and development of microwave spectroscopy and nuclear magnetic resonance (NMR) spectroscopy have much in common. In this Account, we discuss the less widely appreciated connections between the parameters measured using the two techniques. Selected examples from our laboratory and from the recent literature attest to the utility and importance of these connections. For example, how a...

The change in (1)H NMR chemical shifts upon hydrogen bonding was investigated using both experimental and theoretical methods. The (1)H NMR spectra of a number of phenols were recorded in CDCl(3) and DMSO solvents. For phenol, 2- and 4-cyanophenol and 2-nitrophenol the OH chemical shifts were measured as a function of concentration in CDCl(3). The plots were all linear with concentration, the g...

Ring currents can exert a large effect upon the chemical shielding of NMR resonances. The analytical expression developed by Waugh and Fessenden (Waugh, J. S.; Fessenden, R. W. J. Am. Chem. Soc. 1957, 79, 846) and Johnson and Bovey (Johnson, C. E.; Bovey, F. A. J. Chem. Phys. 1957, 29, 1012) only quantifies the contribution of ring currents to the isotropic component of the shielding tensor. In...

Ring formation in phosphate systems is expected to influence both the magnitude and orientation of the phosphorus (P) nuclear magnetic resonance (NMR) chemical shielding anisotropy (CSA) tensor. Ab initio calculations of the P CSA tensor in both cyclic and acyclic phosphate clusters were performed as a function of the number of phosphate tetrahedral in the system. The calculation of the P CSA t...

Magnesium oxide nanoclusters have attracted much attention due to their potential applications to catalysis and novel optoelectronic materials. In the present study, we have studied the electronic and magnetic properties of the stoichiometric magnesium oxide nanoclusters (MgO)n  for n = 2-20. Although the binding energy increases with the size of the cluster, it  re...

The structures of the β- and t-LaOF phases have been refined from XRPD patterns. For both phases, (19)F and (139)La solid-state NMR spectra recorded at high magnetic fields show the presence of a single F and a single La local environment, indicating a full anionic ordering in these oxyfluoride compounds. DFT calculations of the (19)F and (139)La chemical shielding tensors and of the (139)La EF...

We report the observation of a new decoupling-induced recoupling phenomenon in multiple-quantum magic-angle-spinŽ . ning MQMAS NMR spectra of half-integer quadrupolar nuclei. The origin of the effect is identical to the second-order Ž . recoupling between dipolar and anisotropic chemical shielding interactions under continuous-wave CW spin decoupling, w Ž . x which is first observed by Ernst et...

Eight meso-aryl calixphyrin derivatives were synthesized and their conformational equilibria and transitions studied with temperature-dependent NMR spectroscopy. On the basis of density functional computations, several conformer species could be identified and observed changes in chemical shifts explained. In some compounds, the aryl group rotation and porphyrin ring flipping could be monitored...

A recently developed methodology for calculating, analyzing, and visualizing nuclear magnetic shielding densities is used studying spatial contributions including ring-current to 1H resonance (NMR) chemical shifts of aromatic anti-aromatic free-base porphyrinoids. Our approach allows a visual inspection the origin positive (shielding) negative (deshielding) constants. Diatropic paratropic curre...