Analyzing and Assigning Carbon-13 Chemical-Shift Tensors in α-L-Rhamnose Monohydrate Single Crystals

Abstract

Abstract The carbon-13 chemical-shift tensors of α- L -rhamnose (6-deoxy- L -mannose) monohydrate (C6H12O5·H2O [10030-85-0]) are measured using two-dimensional chemical-shift correlation spectroscopy. The tensors and the orientation of the twofold axis along thebcrystallographic axis in the sample frame are obtained by symmetry-constrained fitting of the data.Ab initiogauge invariant atomic orbital computations of the chemical shielding are then used to assign the tensors to the carbons in the rhamnose molecule and to the two molecules in the unit cell. These computations are also used to find the direction of thebcrystallographic axis along the twofold axis and to make initial estimates of theaandccrystallographic axes in the sample. The finalaandccrystallographic axes are then determined with a 2D dipolar spectrum. A second independent method, 1D spectra taken with the applied field along directions perpendicular to the (011), the (110), and the (100) crystallographic planes, is used to confirm the result.