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After last year’s trilogy about RDC’s, we were very pleased to have Professor Roberto R. Gil back to give another webinar. In this occasion Roberto talked about Residual Chemical Shift Anisotropy, a highly valuable anisotropic NMR parameter for the structural analysis of small organic molecules on May 3.
Residual Chemical Shift Anisotropy (RCSA) is another highly valuable anisotropic NMR parameter for the structural analysis of small organic molecules. Due to the presence of unwanted isotropic chemical shifts, the accurate measurement of RCSAs is not as straightforward as measuring Residual Dipolar Couplings (RDCs),
Two relatively recent articles introduced the application of RCSAs to the analysis of small organic molecules,[1-2] but it was not until a recent seminal article showed that it is possible to discriminate molecular configuration using only RCSAs. This article, in which compressed and stretched PMMA gels swollen in CDCl3 were used to measure 13C RCSAs, has created a lot of enthusiasm in the small molecules community, bringing another orthogonal tool to the already existing pool of NMR experiments.
While RDCs encode information about the relative orientation of internuclear vectors (e.g, C-H bonds), RCSAs encode information about the relative orientation of Chemical Shift Tensors, regardless of the distance between them in both cases. The information provided by this technique is only valuable if the tensors are anisotropic (different values for σ11, σ22 and σ33). Its application is limited if the anisotropy is very small or null. Hence, RCSAs are very useful in molecules containing sp2 carbons (aromatic rings, double bonds, carbonyl groups, etc.). Needless to say the important added value of RCSAs for proton-deficient molecules, where quaternary carbons lack hydrogen atoms in order to have C-H vectors available for RDC analysis.
In the present webinar, basic theoretical concepts, practical aspects to measure RCSAs free of isotropic shift interferences, and their applications to the structural analysis of small organic molecules, will be presented.
 “Variable angle NMR spectroscopy and its application to the measurement of residual chemical shift anisotropy”. Kummerloewe, Grit; Grage, Stephan L.; Thiele, Christina M.; Kuprov, Ilya; Ulrich, Anne S.; Luy, Burkhard. Journal of Magnetic Resonance 2011, 209(1), 19-30.
 “Residual Chemical Shift Anisotropy (RCSA): A Tool for the Analysis of the Configuration of Small Molecules”. Hallwass, Fernando; Schmidt, Manuel; Sun, Han; Mazur, Adam; Kummerloewe, Grit; Luy, Burkhard; Navarro-Vazquez, Armando; Griesinger, Christian; Reinscheid, Uwe M. Angewandte Chemie, International Edition 2011, 50(40), 9487-9490, S9487/1-S9487/27.
 “Determination of Relative Configuration from Residual Chemical Shift Anisotropy” . Nath Nilamoni; Schmidt Manuel; Griesinger Christian; Gil Roberto R; Williamson R Thomas; Martin Gary E; Liu Yizhou; Navarro-Vazquez Armando; Navarro-Vazquez Armando. Journal of the American Chemical Society 2016, 138 (30), 9548-56.
Professor Roberto R. Gil got his Ph.D. in Natural Products Chemistry (1989) from the University of Córdoba, Argentina. In 1992 he received an external post-doctoral fellowship from the National Research Council of Argentina (CONICET) to work at the University of Illinois at Chicago in the field of bioactive natural products from plants.
In 1995, he returned to the University of Córdoba where he started his own research group as Assistant Professor. In 2000 he spent a year as Visiting Professor at Carnegie Mellon University working in Protein NMR.
In 2002, he moved to Pittsburgh, Pennsylvania, where he currently holds the position of Research Professor and Director of the NMR Laboratory of the Department of Chemistry at Carnegie Mellon University. His research interest is aimed at the development and application of NMR methodologies to the analysis of the structural and physical properties of small molecules in general, with particular interest on NMR in oriented media.