New Stretching Method for Aligning Gels: Its Application to the Measurement Residual Chemical Shift Anisotropies (RCSAs) without the Need for Isotropic Shift Correction.

Abstract

An existing gel stretching device is modified, permitting the use of organic solvents for the study of small molecules. Different from the original device, gels are stretched into 4 mm open-ended NMR tubes and then inserted into regular 5 mm NMR tubes. No open-ended tubes are inserted in the NMR probe avoiding the risk of sample leaking. It is also shown that residual chemical shift anisotropies (RCSAs) measured with the device are free of isotropic shift interferences and corrections for them are not needed during the post-acquisition data analysis. Three internal references for chemical shift were evaluated (CCl4 , CBr4 and TMS), being CCl4 the most convenient one to measure RCSAs in CDCl3 . RCSAs measured with the modified stretching device using CCl4 as the internal chemical shift reference were enough to determine the relative configuration of three small molecules with an excellent degree of configuration discrimination.