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1H-Azepine (1)—generated by a new method in solution at −78°C—could be characterized for the first time as a practically uniform seven-membered ring valence tautomer by its 1H- and 13C-NMR spectra. (1) polymerizes very readily. It forms 3H-azepine (2) with catalytic amounts of acid or base. (2) can be vacuum distilled, albeit with considerable losses.
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Vogel et al. (1980) studied this question.
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