Molecular and structural information from 14N–13C dipolar couplings manifested in high resolution 13C NMR spectra of solids

Abstract

The dipolar coupling between 14N and 13C is not suppressed by magic angle sample spinning because the relatively large 14N quadrupole interaction shifts the axis of quantization of the 14N spins away from the direction of the applied field. The resulting 13C resonance line shapes are influenced by the sign, magnitude, and asymmetry parameter of the 14N quadrupole coupling tensor; the internuclear distance; the magnitude of the applied magnetic field; and the orientation of the internuclear vector in the principal axis system of the electric field gradient. It is demonstrated that one or more of these parameters can be determined from the 13C NMR data if the others are known by virtue of single crystal studies or molecular symmetry.

Cucurbit[n]urils (n= 5–8): A Comprehensive Solid State Study

“…In order to further support the solid state structures deduced by single crystal X-ray crystallography, we carried out solid state CP-MAS 13 C NMR experiments at 21.1 T. Also, it was hoped that 13 C solid state NMR spectra would prove to be a useful tool for routine characterization of CB[n] structures. Preliminary results obtained at 7 T showed broad featureless lines due to residual dipolar interactions with the quadrupolar 14 N atoms 46 (of which there are two attached to each carbon). This problem is completely eliminated at 21.1 T, resulting in spectra for the four crystalline materials which display multiple sharp resonances within three narrow regions for each of the chemically distinct carbon types: (i) CdO functions between ∼154À160 ppm, (ii) CÀH groups between ∼67À75 ppm, and (iii) bridging CH 2 groups between ∼49À57 ppm.…”

A carbon-13 nuclear magnetic resonance study of solid tetracyclines

“…In solution, the amide shift is always reported to be upfield of the C12 signal (14), but in the solid this order is occasionally reversed. Typically, the amide resonance appeared as an asymmetric doublet (41,(44)(45)(46) with an apparent splitting of approximately 100 Hz (Fig. 3a).…”

“…The magnitude of the observed splitting is in good agreement with that calculated (47) using the method of Hexem el a / . (45). Assuming a 14N quadrupolar coupling constant of 2.274 MHz (q = 0.378) for thepmide moiety (48) The effect of I4N on the C4 resonance signal is of particular interest.…”

13C and15N—Chemical Shift Anisotropy of Ampicillin and Penicillin-V Studied by 2D-PASS and CP/MAS NMR

“…. 14 N dipolar coupling perturbs the spinning sideband amplitudes, and in addition leads to broadenings and splittings, since 14 N has a strong quadrupolar interaction (38,39). The peak broadening causes overlap with other peaks, and reduced signal-to-noise ratio for these sites.…”

“…Almost all 13 C resonances are resolved. Most of these resonances are singlets but some of them are broadened and split by 13 C-14 N dipole-dipole coupling (38,39). Most of the peak assignments are taken from Clayden et al (3) and are based on a comparison of solid-state and solution NMR spectra (40,41).…”