C-13 CHEMICAL-SHIFT TENSORS IN MESO-ERYTHRITOL, MEASURING OH DIHEDRALANGLES

The carbon-13 chemical shift tensors of meso-erythritol (1,2,3,4-butan etetrol, C4H10O4) were measured from two one-dimensional NMR spectra t aken with the applied field perpendicular to the (110) and (101) cryst al faces. Ab initio gauge invariant atomic orbital (GIAO) chemical shi elding computations were used to assign the spectral lines to the carb ons in the erythritol molecule and the molecules in the unit cell. The conformational disorder in erythritol was treated by taking the weigh ted average of the GIAO results for the two different conformations. T he icosahedral shieldings computed with various weighting factors were then fitted to the experimental icosahedral shifts. Using the neutron diffraction structure the GIAO computations produced shieldings which correlate to the experimental chemical shift tensors with a 1.53 ppm standard deviation. The weighting factor which produced the best fit a grees with the occupancy percentage determined by neutron diffraction. GIAO computations were done for hypothetical O-H bond conformations i n erythritol to investigate the effect of the hydroxyl dihedral angles on carbon-13 tensors.