A Deuterium NMR and Quantum Chemical Study of N — H ... X Hydrogen Bonding in Solids

1. A Deuterium NMR and Quantum Chemical Study of N—H...X Hydrogen Bonding in Solids Renee Webber and Glenn H. Penner Department of Chemistry, University of Guelph, Guelph, Ontario N1G 2W1 2,4,6-Trimethylbenzamide Pyridine-3,5-dicarboxylic acid 1 2 1 2 A hydrogen bonded sheet in pyridine-3,5-dicarboxylic acid. The strong hydrogen bonds (N—H...O and O—H...O) are shown by heavy dashed lines and the weak C—H...O hydrogen bonds are indicated by thin dashed lines. A hydrogen bonded chain in 2,4,6-trimethylbenzamide with N—H...O and N—H... interactions shown by dashed lines. Top:Experimental 2H MAS spectrum of pyridine-3,5-dicarboxylic acid. The two overlapping spectra have been highlighted for clarity (Orange corresponds to hydrogen 1 and blue to hydrogen 2). Bottom: Simulated spectra corresponding to the two distinct hydrogens. Top:Experimental 2H MAS spectrum of 2,4,6-trimethylbenzamide. The two overlapping spectra have been highlighted for clarity (Orange corresponds to hydrogen 1 and blue to hydrogen 2). Bottom: Simulated spectra corresponding to the two distinct hydrogens. • All 2H NMR spectra were obtained on a 500 MHz (11.75 T) spectrometer. • Spectra were simulated using the Simpson Simulation program.5 • The 2,4,6-trimethylbenzamide calculations were performed using a trimer while the pyridine-3,5-dicarboxylic acid calculations were performed with a tetramer. • All calculations were performed with G03 and the B3LYP functional. QCCs were determined using the 6-311G** basis set, whereas NMR calculations used the 6-31G. • Discussion • 2H MAS is advantageous as it allows for the determination of the QCC AND chemical shift for both hydrogens at the same time. • Calculations are in good agreement with the experimental results. • Distinct asymmetries in the manifold of spinning sidebands were observed for both spectra, indicating that the spectra are influenced by CSA.A higher magnetic field is required if more accurate CSA values are to be obtained. • References • M. Gdaniec, T. Olszewska, and T. Polonski, Acta Cryst., 2004, C60, o-41. • J.A. Cowan, J.A.K. Howard, G.J. McIntyre, S. M. F. Lo and I. D. Williams, Acta Cryst., 2005, B61, 724. • E. Brunner and U. Sternberg, Nuclear Magn. Reson. Spec., 1998, 32, 21. • T. Chiba, J. Chem. Phys., 1964, 41,1352. • (5)M. Bak, J. T. Rasmussen and N.C. Nielsen, J. Magn. Reson.,2000, 147, 296. • This research was funded by a grant from the Natural Sciences and Engineering Research Council of Canada • Introduction • The 2H isotropic chemical shift and the quadrupolar coupling constant (QCC) are both sensitive to the bonding state. • The 2H isotropic chemical shift increases with increasing hydrogen bond strength.3 • The QCC decreases with increasing hydrogen bond strength.4 • The degree to which these two parameters are affected by hydrogen bonding can be determined both experimentally and via quantum chemical calculations. • Experimental • 2,4,6-Trimethylbenzamide was synthesized by bubbling ammonia gas through 2,4,6-trimethylbenzoyl chloride in CH2Cl2.