Supramolecular Structure of Phenyl Derivatives of Butanol Isomers

Wide-angle X-ray scattering patterns were recorded for a series of aliphatic butanol isomers (n-, iso-, sec-, tert-butanol) and their phenyl derivatives (4-phenyl-1-butanol, 2-methyl-3-phenyl-1-propanol, 4-phenyl-2-butanol, and 2-methyl-1-phenyl-2-propanol, respectively) to determine their atomic-scale structure with particular emphasis on the formation of supramolecular clusters. In addition, molecular dynamics simulations were carried out and yielded good agreement with experimental data. The combination of experimental and theoretical results allowed clarification of the origin of the pre-peak appearing at low scattering angles for the aliphatic butanols and its absence for their phenyl counterparts. It was demonstrated that the location of the hydroxyl group in the molecule of alkyl butanol, its geometry, and rigidity determine the morphology of the supramolecular clusters, while the addition of the aromatic moiety causes more disordered organization of molecules. The phenyl group significantly decreases the number of hydrogen bonds and size of the supramolecular clusters formed via the O–H···O scheme. The lower association ability of phenyl alcohols via H-bonds is additionally attenuated by the appearance of competing π–π configurations evidenced by the structural models.本研究针对一系列脂肪族丁醇异构体（正丁醇、异丁醇、仲丁醇、叔丁醇）及其苯基衍生物（依次为4-苯基-1-丁醇、2-甲基-3-苯基-1-丙醇、4-苯基-2-丁醇与2-甲基-1-苯基-2-丙醇）采集了广角X射线散射（Wide-angle X-ray scattering）图样，以解析其原子尺度结构，重点关注超分子团簇（supramolecular clusters）的形成过程。此外，本研究还开展了分子动力学模拟，所得结果与实验数据吻合度极佳。结合实验与理论结果，本研究阐明了脂肪族丁醇在低散射角处出现预峰的成因，以及其苯基衍生物无该预峰的缘由。研究表明，烷基丁醇分子中羟基的位置、空间构型与刚性程度决定了超分子团簇的形貌；而芳香基团的引入则会使分子排列更趋无序。苯基基团可显著减少通过O–H···O氢键作用形成的超分子团簇的数量与尺寸。结构模型证实，竞争性π-π堆积构型的出现进一步削弱了苯基醇通过氢键进行缔合的能力。