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Carbon-Carbon and Carbon-Nitrogen Spin-Spin Coupling in NMR Spectroscopy: Simple Examples Based on Isotope-Labeled Glycines

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Leif Grehn , Ulf Ragnarsson and Christopher J. Welch

Organic Pharmaceutical Chemistry, Uppsala Biomedical Centre, Department of Pharmaceutical Chemistry, Uppsala Biomedical Centre, Box 574, Uppsala S-751 23 SWEDEN

J. Chem. Educ., 1997, 74 (12), p 1477

DOI: 10.1021/ed074p1477

Publication Date (Web): December 1, 1997

Section:

History, Education, and Documentation

Abstract

The phenomena of carbon-carbon and carbon-nitrogen spin-spin coupling, not visible in ¹³C and ¹⁵N NMR spectra recorded at natural abundance, are demonstrated using routine conditions primarily in a series of ¹³C/¹⁵N-labeled t-butoxycarbonyl- glycine isotopomers. Doublet and doublet of doublet signals, originating from one and two bond homo- and/or heteronuclear spin-spin coupling, are thereby obtained. Furthermore, from all these NMR spectra the presence of each isotopomer in two con formations is clearly demonstrated. Such compounds are in principle easy to make, but preparative work especially involving the ¹³C nucleus is costly, for which reason two other more affordable alternatives are also presented, based only on ¹⁵N labeling, in which cases ¹³C nuclei directly attached to ¹⁵N give rise to doublet signals. These two preparations can conveniently be performed on a small scale. The first one involves the synthesis of a ¹⁵N-labeled imidodicarbonate, whereas the second demonstrates its efficient alkylation under simple phase-transfer catalysis conditions.