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Electron spin resonance study of the chlorpromazine cation Tapping, Robert L.


The cation radical of chlorpromazine in solution was studied in detail by electron spin resonance. The 16 line spectrum was interpreted in terms of a nitrogen atom, two equivalent protons at the first side chain carbon atom, and three almost equivalent protons from the ring system. The relative magnitudes of the splitting constants require many of the spectral lines to be coincident, and the result is the 16 line spectrum observed. Analysis of the splitting constants was done using Huckel molecular orbital calculations, from which it was deduced that the chlorpromazine cation structure is folded about the N-S axis, with an included angle of 104°. The spectral asymmetry observed in sulfuric acid solution was interpreted in terms of random molecular motions causing a fluctuating environment to arise at the nuclear positions. This leads to a modulation effect on the nuclear magnetic moment, and is responsible for linewidth variation. Further broadening due to exchange effects is discussed qualitatively. The asymmetry of the spectra enable the sign of the nitrogen splitting to be estimated -- it was found to be positive. A brief discussion of the electrical properties of chlorpromazine, using HMO calculations, was included, and some discussion of the mechanism of chlorpromazine drug action was also considered for completeness.

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