Electron Spin Resonance Spectrum of the Radical Anion of 1,3-Butadiene in Liquid Ammonia

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Abstract
The electron spin resonance spectrum of the radical anion of 1,3‐butadiene has been observed by means of continuous electrolysis in liquid ammonia. The proton coupling constants were observed to be A(CH)=2.791±0.007 Oe and A(CH2)=7.617±0.005 Oe. These values give a Q(av)=20.82±0.02 Oe. The source of this low Q value is discussed together with theoretical spin densities. Simple Hückel theory predicts a spin density ratio of 2.615 which can be compared with the observed coupling constant ratio of 2.729±0.007. The predictions of Parr and Mulliken's SCF theory are much less satisfactory and give a low spin‐density ratio. Electrolysis in liquid ammonia appears to be an excellent method for the generation of radical anions.