Prediction of 11B Quadrupole Coupling Constants in Molecules

Multinuclear Residual Quadrupolar Couplings for Structure and Assignment

Most stable isotopes have a nuclear spin >1/2, but the quadrupole interaction poses challenge on their detection by nuclear magnetic resonance (NMR). On the other hand, the quadrupole interaction is a rich source of structural information that may be exploited for solution NMR in the form of residual quadrupolar couplings (RQCs) of weakly oriented samples. While 2H RQCs are now well established for structure verification and enantiomeric discrimination of organic molecules, we will in this article highlight some recent work on RQCs of other nuclei (especially 7Li and 11B).

Resonance and structural assignment in (car)borane clusters using 11B residual quadrupolar couplings

A new NMR method for structural verification and 11B resonance assignment in (car)borane clusters is presented, based on the measurement of 11B residual quadrupolar couplings (RQCs) in a stretched polystyrene (PS) gel. The method was applied to ortho-carborane (B10C2H12), a derivative thereof with reduced symmetry, meta-carborane and decaborane (B10H14).

A combined deuterium NMR and quantum chemical investigation of inequivalent hydrogen bonds in organic solids

Deuterium magic angle spinning (MAS) NMR spectroscopy and quantum chemical calculations are used to investigate organic solids in which inequivalent hydrogen bonds are present. The use of (2)H MAS allows one to measure the chemical shift, δ, quadrupolar coupling constant, C(Q), and asymmetry in the quadrupolar interaction, η(Q), for each type of hydrogen bond present in the system. Quantum chemical calculations of the magnetic shielding (σ, which can be related to δ) and the electric field gradient (EFG, which can be related to C(Q)) are compared to the experimental results and are discussed with respect to the relative strengths of the hydrogen bonds within each system.

Hyperfine Parameters for Aluminum Hydride: An ab Initio Molecular Orbital Study

An extensive ab initio molecular orbital study of the (27)Al nuclear spin-rotation and nuclear quadrupolar coupling constants in aluminum hydride, AlH, has been performed. The (27)Al nuclear spin-rotation constant (C( perpendicular)), calculated to be approximately 300 kHz, was neglected in a previous analysis of the hyperfine structure in the microwave spectrum (M. Goto and S. Saito, Astrophys. J. 452, L147-148 (1995)). Unfortunately, the ab initio calculations do not provide a definitive value for the aluminum nuclear quadrupolar coupling constant, but suggest a value of -49+/-4 MHz. It is apparent that the microwave study of AlH should be repeated. Copyright 2001 Academic Press.

B3LYP Calculation of Deuterium Quadrupole Coupling Constants in Molecules

The B3LYP/6-31G(df,3p) model for the calculation of deuterium nuclear quadrupole coupling constants (nqcc's) is shown to yield results as accurate as calculations previously performed at the MP4 level of theory. For 25 molecules, ranging from HD and DF to pyridine and fluorobenzene, the rms difference between the B3LYP nqcc's and the experimental nqcc's is 3.2 kHz (2.7%). For benzene, our calculations suggest that the experimental chibb and chicc of S. Jans-Bürli, M. Oldani, and A. Bauder, 1989. Mol. Phys., 68, 1111-1123) have been incorrectly assigned with respect to inertia axes and should be reversed. For borane carbonyl and nitric acid, it is shown that nqcc calculations using hydrogen bond lengths given by MP2/6-311 + G(d,p) optimizations in combination with the heavy atom experimental structures significantly improve agreement with the experimental nqcc's. Copyright 1998 Academic Press.