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（分别对应4-苯基-1-丁醇、2-甲基-3-苯基-1-丙醇、4-苯基-2-丁醇及2-甲基-1-苯基-2-丙醇）测得广角X射线散射（Wide-angle X-ray scattering）图谱，旨在解析其原子尺度结构，并重点关注超分子簇（supramolecular clusters）的形成过程。此外，本研究开展了分子动力学模拟（molecular dynamics simulations），所得结果与实验数据吻合良好。结合实验与理论结果，本研究阐明了脂肪族丁醇在小散射角处出现预峰（pre-peak）、而其苯基衍生物无该预峰的成因。研究表明，烷基丁醇分子中羟基的位置、几何构型与分子刚性共同决定了超分子簇的形貌；而芳香基团（aromatic moiety）的引入会使分子排列更趋无序。苯基基团可显著减少通过O–H···O氢键模式（O–H···O scheme）形成的氢键数目与超分子簇的尺寸。经结构模型证实，竞争性π-π堆积构型（π–π configurations）的出现进一步削弱了苯基醇通过氢键形成的缔合能力。