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We have presented a systematic experimental and theoretical investigation of the carbonyl oxygen electric-field-gradient (EFG) tensor and chemical shielding (CS) tensor in crystalline amides. Three 17 O-labled secondary amides, R 1 C[ 17 O]-NHR 2 , have been synthesized: benzanilide (1), N-methylbenzamide (2), and acetanilide (3). Analysis of 17 O magic-angle spinning (MAS) and stationary NMR spectra yields not only the magnitude but also the orientation of the carbonyl 17 O EFG and CS tensors. For compounds 1-3, the carbonyl 17 O quadrupolar coupling constant (QCC) and the span of the chemical shift tensor are found to be in the range of 8.5-8.97 MHz and 560-630 ppm, respectively. The largest 17 O EFG component lies in the amide plane and is perpendicular to the CdO bond, whereas the smallest component is perpendicular to the N-Cd O plane. For the carbonyl 17 O CS tensor, the principal component with the largest shielding, δ 33 , is perpendicular to the amide plane, and the tensor component corresponding to the least shielding, δ 11 , is in the amide plane approximately 20°off the direction of the CdO bond. Extensive quantum chemical calculations using density functional theory (DFT) have been performed for both isolated and hydrogen-bonded molecules of compounds 1-3. The calculated carbonyl 17 O EFG and CS tensors from the latter molecular models are in reasonably good agreement with the experimental values. In particular, the B3LYP/D95** EFG calculations overestimate the carbonyl 17 O QCC by approximately 0.5 MHz. The B3LYP/D95**/GIAO shielding calculations yield a linear correlation between the calculated and experimental data (slope ) 1.125 and R 2 ) 0.9952). The quantum chemical calculations indicated that the intermolecular CdO‚‚‚H-N hydrogen-bonding interactions play an important role in determining the carbonyl oxygen EFG and CS tensors for an amide functional group.

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We have successfully developed a 1020MHz (24.0T) NMR magnet, establishing the world's highest magnetic field in high resolution NMR superconducting magnets. The magnet is a series connection of LTS (low-Tc superconductors NbTi and Nb3Sn) outer coils and an HTS (high-Tc superconductor, Bi-2223) innermost coil, being operated at superfluid liquid helium temperature such as around 1.8K and in a driven-mode by an external DC power supply. The drift of the magnetic field was initially ±0.8ppm/10h without the (2)H lock operation; it was then stabilized to be less than 1ppb/10h by using an NMR internal lock operation. The full-width at half maximum of a (1)H spectrum taken for 1% CHCl3 in acetone-d6 was as low as 0.7Hz (0.7ppb), which was sufficient for solution NMR. On the contrary, the temporal field stability under the external lock operation for solid-state NMR was 170ppb/10h, sufficient for NMR measurements for quadrupolar nuclei such as (17)O; a (17)O NMR measurement for labeled tri-peptide clearly demonstrated the effect of high magnetic field on solid-state NMR spectra.