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Article

An ABMX Spin System Study: From Experimental to Calculated Spectra

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Christine Cordier

ITODYS, Université Paris, Paris, France

René Thouvenot , Hani Amouri and Michel Gruselle

Laboratoire de Chimie Inorganique et Matériaux Moléculaires, Université Paris, Paris, France

J. Chem. Educ., 2002, 79 (2), p 234

DOI: 10.1021/ed079p234

Publication Date (Web): February 1, 2002

Section:

History, Education, and Documentation

Abstract

The ¹H NMR spectrum of the stable organometallic cation [Co₂(CO)₅(μ-HCCCH₂-PΦ₂-CH₂-PΦ₂]⁺ displays both ABX and ABMX subspectra. The experimental analysis of these spin systems is carried out by means of a set of ¹H and ³¹P NMR spectra. Techniques of selective decoupling of each of the phosphorus nuclei and ³¹P broad-band decoupling jointly to proton selective decouplings drastically simplify the examination of such subspectra and allow an unambiguous assignment of their signals. In addition, ¹H-¹H coupling constants are estimated. The theoretical investigation of spin systems containing nuclei strongly coupled is intended for students of a graduate level spectroscopy course. In this work, the quantum mechanical treatment of the ABX and ABMX models is developed. With this information and the experimental coupling constants, students are able to generate a calculated ABX or ABMX subspectrum. The spectral simulation with appropriate software (such as gNMR) allows students to confirm the signal assignment for the ¹H spectrum and to compare the calculated coupling constants with the experimental data.