CPMAS 13C NMR Spectra of Quinones, Hydroquinones, and Their Complexes. Use of CMR To Follow a Reaction in the Solid State

Article abstract of DOI:10.1021/ja00303a014

CPMAS 13C NMR spectroscopy has been employed to follow the reaction at temperatures above 70 deg C of the crystalline 1/1 complex of 1,4-benzoquinone with 2,5-dimethyl-1,4-hydroquinone to give the 1/2 complex of 2,5-dimethyl-1,4-benzoquinone-hydroquinone and an equimolar amount of 2,5-dimethyl-1,4-benzoquinone.The redox reaction of a solid mixture of quinhydrone (1,4-benzoquinone-1,4-hydroquinone) with an equimolar amount of 2,5-dimethyl-1,4-hydroquinone gives the 1/2 complex of 2,5-dimethyl-1,4-benzoquinone with 1,4-hydroquinone with no evidence of formation of side products or accumulation of reaction intermediates.During preparation of a mixture of the 1/1 complex of 1,4-benzoquinone-2,5-dimethylhydroquinone with an equimolar amount of 1,4-hydroquinone the partial exchange of one hydroquinone for another in the complex occurs even during mixing of the components at room temperature.An equimolar mixture of 1,4-benzoquinones, 1,4-hydroquinone, and 2,5-dimethyl-1,4-hydroquinone underwent partial complexation at room temperature.These latter two mixtures when heated in the solid state each gave the 1/2 complex 2,5-dimethyl-1,4-benzoquinone-1,4-hydroquinone.As background for this work, CMR spectra of some crystalline quinones, hydroquinones, and their complexes (quinhydrones) have been obtained.The differences between the solid-state and corresponding solution spectra have been shown to be primarily in the multiplicities of some resonances but not others.It is suggested that a primary source of multiplicities in the quinones is CH---O interactions of the sort discussed by others in the analysis of the crystal packing patterns of such compounds.