Abstract

Possible anomalies of gas chromatographic retention indices (RIs) for homologs are difficult to determine as they are masked by the “normal” homologous dependence (~100 index units per CH₂ homologous difference). A comparison of the RIs of homologs in the form of their homologous increments i_RI = RI – 100x (х = int(M/14), where int is the integer part of the number equivalent to M = 14x + y_М, where у_М is the number of the homologous group of the compound; y_М ≡ M(\(\bmod 14\))) revealed two anomalies of chromatographic retention, which were not discussed previously. One of these is abnormal decrease in i_RI of di-n-alkyl phthalates at increased number of carbon atoms in alkyl fragments, which is not associated with variations in their polarity or polarizability. The most probable reason is the position of the conformational equilibria of the alkyl fragments of molecules (predominantly “folded” into Gaussian coils) in the molecules of ortho-disubstituted aromatic compounds. Among the numerous theoretically possible structures of this type, the largest number of homologs with different numbers of carbon atoms, which makes it possible to trace the anomalies of their gas chromatographic properties, was characterized only in the series of dialkyl phthalates. The second anomaly relates to polymethyl-substituted aromatic compounds containing substituents at ortho-positions relative to each other. The presence of this structural fragment leads to an anomalous increase in the i_RI values of homologs, which is also not related to their polarity or polarizability, but can be explained by steric hindrances to the intramolecular rotation of substituents relative to С(sp²)–C(sp³) ordinary bonds (“gear effect”). Both effects are compared with the so-called “propyl group effect” discussed in the 1980s, whose value does not exceed 10 index units for aliphatic dienes; in the given cases, the RI anomalies reach 160 units for dialkyl phthalates and 150 index units for methylbenzenes and methylnaphthalenes.

中文翻译：

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基于同源增量的同源物气相色谱保留指数异常测定

摘要

同源物的气相色谱保留指数 (RI) 的可能异常难以确定，因为它们被“正常”同源依赖性（每个 CH ₂同源差异约 100 个索引单位）所掩盖。以同源增量i _RI = RI – 100 x ( х = int( M /14)的形式比较同系物的_RI，其中 int 是等于M = 14 x + y _М的数字的整数部分，其中у _М是化合物的同源基团的数目；y _М ≡ M ( \(\bmod 14\))) 揭示了色谱保留的两个异常，这在之前没有讨论过。其中之一是在烷基片段中碳原子数增加时邻苯二甲酸二正烷基酯的i _RI异常降低，这与其极性或极化率的变化无关。最可能的原因是分子的烷基片段（主要“折叠”成高斯线圈）在邻位分子中的构象平衡位置。-双取代的芳香族化合物。在这种类型的众多理论上可能的结构中，具有不同碳原子数的同系物数量最多，这使得追踪其气相色谱特性的异常成为可能，仅在邻苯二甲酸二烷基酯系列中表征。第二个异常与多甲基取代的芳族化合物有关，它们在彼此的邻位上含有取代基。该结构片段的存在导致同系物的i _RI值异常增加，这也与其极性或极化率无关，但可以通过取代基相对于 С( sp ² )的分子内旋转的空间位阻来解释-C（sp ³ ) 普通债券（“齿轮效应”）。将这两种效应与 1980 年代讨论的所谓“丙基效应”进行比较，其值不超过脂肪族二烯的 10 个指标单位；在给定的情况下，邻苯二甲酸二烷基酯的 RI 异常达到 160 个单位，甲苯和甲基萘的 RI 异常达到 150 个指数单位。