1H-detected, gradient-enhanced 15N and 13C NMR experiments for the measurement of small heteronuclear coupling constants and isotopic shifts

Otting, G., Messerle, B. A. and Soler, L. P. (1996) 1H-detected, gradient-enhanced 15N and 13C NMR experiments for the measurement of small heteronuclear coupling constants and isotopic shifts. Journal of the American Chemical Society, 118(21), pp. 5096-5102. (doi: 10.1021/ja9540177)

Abstract

A suite of 1H-detected, gradient-enhanced experiments is presented for the measurement of small 1H−15N and 13C−15N coupling constants in small organic compounds, where no protons are directly bound to the nitrogens. The experiments are based on modified HMQC pulse sequences and a novel gradient supported half-filter element. The experiments were applied to obtain a complete set of coupling constants in tris(1-pyrazolyl)methane (1), where 6% of the aromatic ring systems were doubly enriched with 15N. The absolute sign of the 1H−1H, 1H−15N, 13C−15N, and 15N−15N coupling constants was determined by relating them to the sign of a one-bond 1H−13C coupling constant. The experiments also yield multiple bond 13C/12C isotope effects on the 15N chemical shifts. The 1H−15N and 13C−15N coupling constants in 1 are non-uniform, with some of the short-range coupling constants smaller than the longer range coupling constants. In contrast, all one-bond 13C/12C isotope effects on the 15N chemical shifts were observed to be significantly larger than the isotope effects mediated via two or more bonds. The one-bond isotope effect thus provides a valuable tool for assigning 15N resonances in cases where coupling constant data yield ambiguous results.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Soler, Dr Linnea
• Authors: Otting, G., Messerle, B. A., and Soler, L. P.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Journal of the American Chemical Society
• Publisher: American Chemical Society
• ISSN: 0002-7863
• ISSN (Online): 1520-5126