1. Purpose

The basic COSY pulse sequence (see Exp. 10.3) works best for spin-spin coupling constants of 3 to 15 Hz. With the long-range variant it is possible to observe cross- peaks for protons that are connected by a very small coupling constant (as in allylic, homoallylic, or W-coupling). The method succeeds even in cases where the spin coupling is not resolved in the normal 1D ¹H NMR spectrum.

2. Literature

[1] A. Bax, R. Freeman, J. Magn. Reson. 1981, 44, 542-561.

[2] T. D. W. Claridge, High-Resolution NMR Techniques in Organic Chemistry, Pergamon, Oxford, 1999, 199-200.

3. Pulse Scheme and Phase Cycle

4. Acquisition

Time requirement: 25 min Sample: 5% ethyl crotonate in CDCl₃ Record a normal ¹H NMR spectrum and optimize the spectral width. Change to the 2D mode of the spectrometer software and load the long-range COSY pulse program. You td2: | k data points in F; tdl: 128 data points in F, sw2: 8 ppm swl: 8 ppm o1: middle of ¹H NMR spectrum p!,p2: 90° ¹H transmitter pulse d1: 2s