Determination of Relative Configuration from Residual Chemical Shift Anisotropy

What is it about?

Assigning the configuration of stereogenic centers remains one of the most difficult challenges of molecular structure characterization. Methods such as NOE or J-based configuration analysis are useful but across limited distances. The potential of RCSAs has long been known but the utilization of this fundamental parameter has been impeded by the difficulty of removing the isotropic component of the chemical shift. The inherent difficulties of isotropic contributions to the chemical shift have been surmounted, making the measurement of RCSA a useful technique for the assignment of configuration. The technique is based on the simple measurement of 13C chemical shifts under two different alignments. Quite usefully, RCSAs are also useful for assigning the configuration of non-protonated carbons in contrast to RDCs which can only be used when very low sensitivity long-range RDCs are measured.

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Why is it important?

The utilizaiton of RCSAs to assign configuration provide a powerful new tool and works for both protonated and non-protonated stereogenic carbons.