NMR Spectroscopy in Lipophilic Solutions

Oxygen-17 Chemical Shifts for Selected Coordination Types3 

Tetrahedral O (acyclic, bridging) Tetrahedral O (cyclic, terminal) Tetrahedral O (cyclic, bridging) Octahedral O or OH (terminal) Pentacoordinate O (terminal) 

Similar to the situation for quadrupole-induced relaxation, the quadrupole splitting in liquid crystals is zero if the molecular symmetry is tetrahedral or higher. Electric field gradients are zero for such symmetries so there can be no quadrupolar interaction. However, one expects to see small splittings from tetrahedral or octahedral derivatives because of structural distortions. These predominately arise from specific interactions with extraneous materials such as lipophilic headgroups in surfactant systems, as seen, for instance, in both cationic and anionic octahedral cobalt(III) species [23], Much larger splittings will be expected from other structure 

FIGURE 2.3 51V NMR spectrum of vanadate in a nematic lyotropic liquid crystalline solution. The spectrum shows quadrupole-split signals from V and V4, while the signal of V2 is broadened. The quadrupole splittings are 200 Hz and 5.35 kHz for V and V4, respectively. The spectrum was obtained from a tetradecyltrimethylammonium bromide (TDTMABr) mesophase of composition TDTMABr, 160 mg decanol, 30 mg D20,450 mg NaCl, 10 mg. 

The anisotropy in the chemical shift of nucleus i (aia) is related to the chemical shift tensor and the elements of the order matrix, as shown in Equation 2.7. 

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