1. Purpose

Complex spin systems can be simplified by homonuclear decoupling. By this technique residual multiplets are obtained in which the spin coupling to the irradiated proton is missing. The signal of the irradiated proton itself cannot be observed during decoupling. From a comparison with the undisturbed multiplet the relevant spin coupling constant can be evaluated. Similar information can also be obtained with the selective COSY technique (Exp. 7.5). Here we show a homonuclear decoupling experiment on ethyl crotonate.

2. Literature

W. A. Anderson, R. Freeman, J. Chem. Phys. 1962, 37, 85–103.
J. P. Jesson, P. Meakin, G. Kneissel, J. Am. Chem. Soc. 1973, 95, 618–620.
M. L. Martin, J.-J. Delpuech, G. J. Martin, Practical NMR Spectroscopy, Heyden, London, 1980, 203–206.
J. D. Baldeschwieler, E. W. Randall, Chem. Rev. 1963, 63, 81–110.
R. W. Dykstra, J. Magn. Reson. Ser. A 1993, 102, 114–115.

3. Pulse Scheme and Phase Cycle

Homonuclear decoupling sequence with single-frequency proton irradiation

4. Acquisition

Time requirement: 20 min

Sample: 5% ethyl crotonate in CDCl₃.

Load standard ¹H parameters, record a normal ¹H NMR spectrum, and note the offsets of the signals to be irradiated. Change the setup for the spectrometer so that two proton channels are available. Load a pulse program for homonuclear decoupling and adjust