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Elucidation of Molecular Structure Using NMR Long-Range Coupling: Determination of the Single Isomer Formed in a Regiospecific Reaction

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Samuel Delagrange and Françoise Nepveu

Laboratoire Pharmacophores Redox, Phytochimie et Radiobiologie, 35 Chemin des Maraîchers, F-31062 Toulouse Cedex 4, France

J. Chem. Educ., 2000, 77 (7), p 895

DOI: 10.1021/ed077p895

Publication Date (Web): July 1, 2000

Abstract

The experiment presented in this article introduces students to the main concepts of two essential NMR techniques for investigating molecular structure. Heteronuclear multiple bond connectivity (HMBC) and proton-coupled ¹³C NMR are used to determine which isomer, from a possible two, is formed by a regiospecific reaction. The demonstration, based on long-range coupling between quaternary carbons and protons on neighboring carbons, is presented step by step. In the first step, ambiguous carbon signals were assigned with HMBC, which shows the long-range couplings between carbons and protons through two and three covalent bonds. The structure was finally resolved by recording a proton-coupled ¹³C spectrum (using gated decoupling) in which each carbon signal is split into a multiplet by coupling with surrounding protons. The study of both the multiplicity and the corresponding coupling constants gives information that allows the determination of the structure without ambiguity.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Organic Chemistry

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Molecular Properties / Structure

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This article has been cited by 1 ACS Journal articles (1 most recent appear below).

Introducing the gNMR Program in an Introductory NMR Spectrometry Course To Parallel Its Use by Spectroscopists
Jackie M. Rummey and Mary C. Boyce
Journal of Chemical Education2004 81 (5), 762
- Introducing the gNMR Program in an Introductory NMR Spectrometry Course To Parallel Its Use by Spectroscopists
  Jackie M. Rummey and Mary C. Boyce
  Journal of Chemical Education2004 81 (5), 762
  Traditional methods of teaching structural elucidation for NMR spectrometry have mimicked spectroscopists' use of peak shift tables and coupling constants. The approach described in this article includes NMR spectral simulation and so parallels ...
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