Density functional theory calculations of hydrogen-bond-mediated NMR J coupling in the solid state.
A recently developed method for calculating NMR J coupling in solid-state systems is applied to calculate hydrogen-bond-mediated (2h) J NN couplings across intra- or intermolecular N-H...N hydrogen bonds in two 6-aminofulvene-1-aldimine derivatives and the ribbon structure formed by a deoxyguanosine derivative. Excellent quantitative agreement is observed between the calculated solid-state J couplings and those previously determined experimentally in two recent spin-echo magic-angle-spinning NMR studies ( Brown, S. P. ; et al. Chem. Commun. 2002, 1852-1853 and Pham, T. N. ; et al. Phys. Chem. Chem. Phys. 2007, 9, 3416-3423 ). For the 6-aminofulvene-1-aldimines, the differences in (2h) J NN couplings in pyrrole and triazole derivatives are reproduced, while for the guanosine ribbons, an increase in (2h) J NN is correlated with a decrease in the N-H...N hydrogen-bond distance. J couplings are additionally calculated for isolated molecules of the 6-aminofulevene-1-aldimines extracted from the crystal with and without further geometry optimization. Importantly, it is shown that experimentally observed differences between J couplings determined by solution- and solid-state NMR are not solely due to differences in geometry; long-range electrostatic effects of the crystal lattice are shown to be significant also. J couplings that are yet to be experimentally measured are calculated. Notably, (2h) J NO couplings across N-H...O hydrogen bonds are found to be of a similar magnitude to (2h) J NN couplings, suggesting that their utilization and quantitative determination should be experimentally feasible.
Joyce
Siân A
SA
Tyndall National Institute, Lee Maltings, Prospect Row, Cork, Ireland.
Yates
Jonathan R
JR
Pickard
Chris J
CJ
Brown
Steven P
SP