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C&E News on our first isotope effect paper

The following article appeared in the September 18, 1995 issue of Chemical and Engineering News

NMR Used to Determine Small Kinetic Isotope Effects

Chemists at Texas A&M University, College Station, have devised a way to employ NMR to simultaneously measure small kinetic isotope effects of all atoms involved in a reaction, using natural abundances of the elements [J. Am. Chem. Soc. 117, 9357 (1995)]. According to the researchers, the technique may make determination of all kinetic isotope effects routine features of investigating reactions. The key step in the method of organic chemistry professor Daniel A. Singleton and graduate student Allen A. Thomas is to isolate the starting materials after the reaction has gone almost to completion. In this way, positive isotope effects show up as great enrichment at each atom position, whereas negative effects show up as great depletion - differences easily seen in NMR. They demonstrated their method with a study of the Diels-Alder reaction of maleic anhydride with isoprene. At 98.9% completion, they distilled off the unreacted isoprene and determined the amount of deuterium and carbon-13 at each position, using the presumably uninvolved methyl group as an internal standard.

 

 

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