The 13C shift tensors for a large variety of olefins including some of the cyclic variety are reported at 20 K. On the basis of existing studies and symmetry arguments the orientation of the tensor elements can in general be assigned to specific molecular axes for the olefmic carbons. With this information conclusions are then drawn, relating trends in the various tensor elements to geometric and electronic effects. The method shows great promise in elucidation of the geometrical origins of chemical shifts. Often the range of shifts encompassed by any individual tensor element is 3 times greater than that of the isotropic shifts in the series. Also described is the apparatus for obtaining 13C cross-polarization spectra at cryogenic temperatures.

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