Nuclear magnetic resonance spectra of the epihalohydrins. I. Signs of long-range spin–spin coupling constants in epichlorohydrin

Abstract

The complete analysis of the proton magnetic resonance spectrum of epichlorohydrin as 10 mole% solutions in benzene and in acetonitrile is reported. Extensive tickling experiments demonstrate that the cisoid coupling constants over four bonds are negative, while the corresponding transoid coupling constants are positive. Detailed results for the benzene solution, in which the non-equivalent protons of the —CH2Cl moiety have almost identical chemical shifts, show that although all the resonances may be unequivocally identified and measured to a high order of precision (± 0.03 Hz), an iterative computer fit (LAOCOON-3) has a larger uncertainty for the derived parameters than indicated by the "probable errors" furnished by the computer program. Analysis of the acetonitrile solution, however, furnishes a less ambiguous result. In addition, it is noted that use of relative apparent intensities of resonance peaks can lead to the wrong sign of those coupling constants whose magnitudes are near zero.