Vishweshwar Peddy, Nangia Ashwini, Lynch Vincent M
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India.
J Org Chem. 2002 Jan 25;67(2):556-65. doi: 10.1021/jo0162484.
X-ray crystal structures of pyrazinic acid 1 and isomeric methylpyrazine carboxylic acids 2-4 are analyzed to examine the occurrence of carboxylic acid-pyridine supramolecular synthon V in these heterocyclic acids. Synthon V, assembled by (carboxyl)O-H...N(pyridine) and (pyridine)C-H...O(carbonyl) hydrogen bonds, controls self-assembly in the crystal structures of pyridine and pyrazine monocarboxylic acids. The recurrence of acid-pyridine heterodimer V compared to the more common acid-acid homodimer I in the crystal structures of pyridine and pyrazine monocarboxylic acids is explained by energy computations in the RHF 6-31G* basis set. Both the O-H.N and the C-H...O hydrogen bonds in synthon V result from activated acidic donor and basic acceptor atoms in 1-4. Pyrazine 2,3- and 2,5-dicarboxylic acids 10 and 11 crystallize as dihydrates with a (carboxyl)O-H...O(water) hydrogen bond in synthon VII, a recurring pattern in the diacid structures. In summary, the carboxylic acid group forms an O-H...N hydrogen bond in pyrazine monocarboxylic acids and an O-H...O hydrogen bond in pyrazine dicarboxylic acids. This structural analysis correlates molecular features with supramolecular synthons in pyridine and pyrazine carboxylic acids for future crystal engineering strategies.
对吡嗪酸1以及异构体甲基吡嗪羧酸2 - 4的X射线晶体结构进行分析，以研究这些杂环酸中羧酸 - 吡啶超分子合成子V的出现情况。合成子V由（羧基）O - H...N（吡啶）和（吡啶）C - H...O（羰基）氢键组装而成，控制着吡啶和吡嗪单羧酸晶体结构中的自组装。通过在RHF 6 - 31G*基组下的能量计算，解释了吡啶和吡嗪单羧酸晶体结构中酸 - 吡啶异二聚体V相较于更常见的酸 - 酸同二聚体I的重现情况。合成子V中的O - H...N和C - H...O氢键均源于1 - 4中被激活的酸性供体和碱性受体原子。吡嗪2,3 - 二羧酸10和2,5 - 二羧酸11以二水合物形式结晶，在合成子VII中存在（羧基）O - H...O（水）氢键，这是二酸结构中的一种常见模式。总之，羧酸基团在吡嗪单羧酸中形成O - H...N氢键，在吡嗪二羧酸中形成O - H...O氢键。这种结构分析将吡啶和吡嗪羧酸中的分子特征与超分子合成子相关联，为未来的晶体工程策略提供了依据。
