2-(methylthio)benzoic acid (1) is an ortho-substituted benzoic acid derivative, whereas 4-(methylthio)benzoic acid (2) is a para-substituted benzoic acid derivative. The structural analysis of both compounds was carried out using PXRD data. 2-(methylthio)benzoic acid shows a triclinic system with the P 1 ‾ $P\overline{1}$ space group, whereas 4-(methylthio)benzoic acid shows a monoclinic system and crystallizes in the P21/a space group. The strength, as well as relative contributions of intermolecular hydrogen bonds, have been examined through Hirshfeld surfaces as well as 2D fingerprint plots. A weak intramolecular hydrogen bond was found only in the case of ortho-substituted 2-(methylthio)benzoic acid. Supramolecular frameworks for 1 are formed by the interplay of intramolecular and intermolecular interactions, whereas for 2, intermolecular contacts form supramolecular assemblies. Intermolecular O–H⋯O interactions involving carboxyl groups form the R2 2(8) graph-set motif for both compounds. Theoretical DFT calculations using the B3LYP correlation functional reveal that the energy gap of HOMO–LUMO orbitals in compound 1, with the methylthio moiety in the ortho position relative to the carboxyl group, is lower than that of compound 2, with the methylthio moiety in the para position. Vertical and adiabatic ionization energies are also calculated for both compounds.

中文翻译：

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通过粉末 X 射线衍射、赫什菲尔德表面分析和 DFT 研究确定 2- 和 4-(甲硫基)苯甲酸的结构

2-(甲硫基)苯甲酸(1)是邻位取代的苯甲酸衍生物，而4-(甲硫基)苯甲酸(2)是对位取代的苯甲酸衍生物。使用 PXRD 数据对两种化合物进行结构分析。2-(甲硫基)苯甲酸显示出三斜晶系 磷 1 ‾ $P\上划线{1}$ 空间群，而 4-(甲硫基)苯甲酸显示单斜晶系并在磷21/A空间组。分子间氢键的强度以及相对贡献已通过赫什菲尔德表面和二维指纹图进行了检查。仅在邻位取代的2-(甲硫基)苯甲酸的情况下发现弱分子内氢键。1 的超分子框架是通过分子内和分子间相互作用的相互作用形成的，而对于 2 来说，分子间接触形成超分子组装体。涉及羧基的分子间 O–H⋯O 相互作用形成 R2 2(8) 两种化合物的图形集基序。使用 B3LYP 相关泛函的理论 DFT 计算表明，甲硫基部分位于羧基邻位的化合物 1 中 HOMO-LUMO 轨道的能隙低于甲硫基部分位于羧基邻位的化合物 2。对位。还计算了两种化合物的垂直和绝热电离能。