Nitrogen heterocycles are a class of organic compounds with extremely versatile functionality. Imidines, HN[C(NH)R]2, are a rare class of heterocycles related to imides, HN[C(O)R]2, in which the O atoms of the carbonyl groups are replaced by N—H groups. The useful synthesis of the imidine compounds succinimidine and glutarimidine, as well as their partially hydrolyzed imino–imide congeners, was first described in the mid-1950s, though structural characterization is presented for the first time in this article. In the solid state, these structures are different from the proposed imidine form: succinimidine crystallizes as an imino–amine, 2-imino-3,4-dihydro-2H-pyrrol-5-amine, C4H7N2 (1), glutarimidine as 6-imino-3,4,5,6-tetrahydropyridin-2-amine methanol monosolvate, C5H9N3·CH3OH (2), and the corresponding hydrolyzed imino–imide compounds as amino–amides 5-amino-3,4-dihydro-2H-pyrrol-2-one, C4H6N2O (3), and 6-amino-4,5-dihydropyridin-2(3H)-one, C5H8N2O (4). Imidine 1 was also determined as the hydrochloride salt solvate 5-amino-3,4-dihydro-2H-pyrrol-2-iminium chloride–2-imino-3,4-dihydro-2H-pyrrol-5-amine–water (1/1/1), C4H8N3
+·Cl−·C4H7N3·H2O (1·HCl). As such, 1 and 2 show alternating short and long C—N bonds across the molecule, revealing distinct imino (C=NH) and amine (C—NH2) groups throughout the C—N backbone. These structures provide definitive evidence for the predominant imino–amine tautomer in the solid state, which serves to enrich the previously proposed imidine-focused structures that have appeared in organic chemistry textbooks since the discovery of this class of compounds in 1883.
氮杂环是一类功能极其多样的有机化合物。亚胺(HN[C(NH)R]2)是一类罕见的杂环化合物,与亚胺(HN[C(O)R]2)有关,其中羰基的 O 原子被 N-H 基团取代。亚氨酸化合物琥珀酰亚胺和戊二酰亚胺以及它们的部分水解亚氨酸-亚胺同系物的有用合成方法在二十世纪五十年代中期首次被描述,但本文首次介绍了它们的结构特征。在固态下,这些结构与拟议的亚胺形式不同:琥珀酰亚胺结晶为亚胺,即 2-亚氨基-3,4-二氢-2H-吡咯-5-胺,C4H7N2 (1);戊二胺结晶为 6-亚氨基-3,4,5,6-四氢吡啶-2-胺甲醇单溶物,C5H9N3-CH3OH (2)、以及相应的水解亚氨基-亚酰胺化合物氨基-酰胺 5-氨基-3,4-二氢-2H-吡咯-2-酮,C4H6N2O (3) 和 6-氨基-4,5-二氢吡啶-2(3H)-酮,C5H8N2O (4)。此外,还测定了亚胺 1 的盐酸盐溶液 5-氨基-3,4-二氢-2H-吡咯-2-亚胺氯化物-2-亚胺-3,4-二氢-2H-吡咯-5-胺-水(1/1/1),C4H8N3
+-Cl--C4H7N3-H2O(1-HCl)。因此,1 和 2 在整个分子中显示出交替的长短 C-N 键,在整个 C-N 主干中显示出明显的亚氨基(C=NH)和胺(C-NH2)基团。这些结构为固态中占主导地位的亚氨基-胺同分异构体提供了确凿证据,丰富了自 1883 年发现这类化合物以来有机化学教科书中出现的以前提出的以亚氨基为中心的结构。