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Weak hydrogen bonds are increasingly hypothesized to play key roles in a wide range of chemistry from catalysis to gelation to polymer structure. Here, 15 N/ 13 C spin-echo magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) experiments are applied to "view" intermolecular CH···N hydrogen bonding in two selectively labeled organic compounds, 4-[ 15 N] cyano-4'-[ 13 C 2 ] ethynylbiphenyl ( 1 ) and [ 15 N 3 , 13 C 6 ]-2,4,6-triethynyl-1,3,5-triazine ( 2 ). The synthesis of 2- 15 N 3 , 13 C 6 is reported here for the first time via a multistep procedure, where the key element is the reaction of [ 15 N 3 ]-2,4,6-trichloro-1,3,5-triazine ( 5 ) with [ 13 C 2 ]-[(trimethylsilyl)ethynyl]zinc chloride ( 8 ) to afford its immediate precursor [ 15 N 3 , 13 C 6 ]-2,4,6-tris[(trimethylsilyl)ethynyl]-1,3,5-triazine ( 9 ). Experimentally determined hydrogen-bond-mediated 2h J CN couplings (4.7 ± 0.4 Hz ( 1 ) and 4.1 ± 0.3 Hz ( 2 )) are compared with density functional theory (DFT) gauge-including projector augmented wave (GIPAW) calculations, whereby species-independent coupling values 2h K CN (29.0 × 10 19 kg m -2 s -2 A -2 ( 1 ) and 27.9 × 10 19 kg m -2 s -2 A -2 ( 2 )) quantitatively demonstrate the J couplings for these "weak" CH···N hydrogen bonds to be of a similar magnitude to those for conventionally observed NH···O hydrogen-bonding interactions in uracil ( 2h K NO : 28.1 and 36.8 × 10 19 kg m -2 s -2 A -2 ). Moreover, the GIPAW calculations show a clear correlation between increasing 2h J CN (and 3h J CN ) coupling and reducing C(H)···N and H···N hydrogen-bonding distances, with the Fermi contact term accounting for at least 98% of the isotropic 2h J CN coupling.

A disaccharide is a challenging case for high-resolution (1)H solid-state NMR because of the 24 distinct protons (14 aliphatic and 10 OH) having (1)H chemical shifts that all fall within a narrow range of approximately 3 to 7 ppm. High-resolution (1)H (500 MHz) double-quantum (DQ) combined rotation and multiple pulse sequence (CRAMPS) solid-state NMR spectra of beta-maltose monohydrate are presented. (1)H-(1)H DQ-SQ CRAMPS spectra are presented together with (1)H (DQ)-(13)C correlation spectra obtained with a new pulse sequence that correlates a high-resolution (1)H DQ dimension with a (13)C single quantum (SQ) dimension using the refocused INEPT pulse-sequence element to transfer magnetization via one-bond (13)C-(1)H J couplings. Compared to the observation of only a single broad peak in a (1)H DQ spectrum recorded at 30 kHz magic-angle spinning (MAS), the use of DUMBO (1)H homonuclear decoupling in the (1)H DQ CRAMPS experiment allows the resolution of distinct DQ correlation peaks which, in combination with first-principles chemical shift calculations based on the GIPAW (Gauge Including Projector Augmented Waves) plane-wave pseudopotential approach, enables the assignment of the (1)H resonances to the 24 distinct protons. We believe this to be the first experimental solid-state NMR determination of the hydroxyl OH (1)H chemical shifts for a simple sugar. Variable-temperature (1)H-(1)H DQ CRAMPS spectra reveal small increases in the (1)H chemical shifts of the OH resonances upon decreasing the temperature from 348 K to 248 K.

Solid-state (25)Mg magic angle spinning nuclear magnetic resonance (MAS NMR) data are reported from a range of organic and inorganic magnesium-oxyanion compounds at natural abundance. To constrain the determination of the NMR interaction parameters (delta(iso), chi(Q), eta(Q)) data have been collected at three external magnetic fields (11.7, 14.1 and 18.8 T). Corresponding NMR parameters have also been calculated by using density functional theory (DFT) methods using the GIPAW approach, with good correlations being established between experimental and calculated values of both chi(Q) and delta(iso). These correlations demonstrate that the (25)Mg NMR parameters are very sensitive to the structure, with small changes in the local Mg(2+) environment and the overall hydration state profoundly affecting the observed spectra. The observations suggest that (25)Mg NMR spectroscopy is a potentially potent probe for addressing some key problems in inorganic materials and of metal centres in biologically relevant molecules.

The (13)C CPMAS spectrum is presented for the polymorph of oxybuprocaine hydrochloride which is stable at room temperature, i.e. Mod. II degrees . It shows crystallographic splittings arising from the fact that there are two molecules, with substantially different conformations, in the asymmetric unit. An INADEQUATE two-dimensional experiment was used to link signals for the same independent molecule. The chemical shifts are discussed in relation to the crystal structure. Of the four ethyl groups attached to NH(+) nitrogens, one gives rise to unusually low chemical shifts, very different from those of the other three ethyl groups. This is attributed empirically to gamma-gauche conformational effects, as is confirmed by shielding computations. These considerations allow (13)C signals to be assigned to specific carbons in the two crystallographically inequivalent molecules in the crystal structure. Indeed, information about the conformations is inherent in the NMR spectrum, which thus provides data of crystallographic significance. A (13)C/(1)H HETCOR experiment enabled resolution to be obtained in the (1)H dimension and allowed (1)H and (13)C signals for the same independent molecule to be linked.