Proton Spin Echo NMR Spectra of 1,1-Difluoro-2,2-dichloroethane: Subspectral Analysis

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Abstract
Fourier transformspin echoNMRspectra have been obtained for the protons in 1,1‐difluoro‐2,2‐dichloroethane as a function of rf pulse spacing. It is shown theoretically and experimentally that spin echospectra for this ABX2 spin system can be analyzed in terms of three distinct subspectra of the AB variety. Effects of transverse relaxation are considered. In principle cross relaxation invalidates subspectral analysis, but for the case of 1,1‐difluoro‐2,2‐dichloroethane such effects are shown to be small. The spin echospectra yielded a precise value for the proton proton coupling constant, J AB =3.471± 0.011 Hz , and somewhat less precise values for the other spectral parameters. A few partially relaxed spectra were obtained by Fourier transformation of the free precession following individual spin echoes. The results of these experiments are in accord with previously developed theory, and show that derivation of selective relaxation rates from such spectra of coupled spin systems may be difficult in practice.