Vysotsky Yu B, Bryantsev V S, Boldyreva F L, Fainerman V B, Vollhardt D
Donetsk State University of Economics and Trade, 31 Shchorsa Str., 83050 Donetsk, Ukraine.
J Phys Chem B. 2005 Jan 13;109(1):454-62. doi: 10.1021/jp048240e.
In the framework of quantum chemical PM3 approximation, the geometrical structure and thermodynamic functions characteristics of the formation of monomers (n = 1-14, 34), dimers (n = 1-14, 34), and trimers and tetramers (n = 1-8) of fluoroalkanols with the composition C(n)F(2)(n+1)CH(2)CH(2)OH are calculated. It is shown that, in contrast to the fatty alcohols, which have a flat zigzag structure, the fluoroalkanol monomers are helical with an average backbone torsion angle equal to 162 degrees. For the minimum-energy structure of dimers, the self-organization of the molecules in a dimer was observed; that leads to an opposite alternation of the torsion angles corresponding to the matching atoms in the two molecules that form the dimer. This results in the fact that the most stable conformation of the dimer is the double helix. The lead (39.5 A) and diameter (7.3 A) of the double helix are determined from the calculations of C(34)F(69)CH(2)CH(2)OH dimers. Enthalpy, entropy, and Gibbs energy of the clusterization are shown to be linearly dependent on the length of the fluorinated chain. From the analysis of these thermodynamic quantities, it is concluded that dimerization of fluoroalkanols at the air/water interface takes place if the hydrocarbon link number exceeds 6, whereas for ordinary alcohols this characteristic number is 11. These calculated values agree with experimental data. The additive scheme for the evaluation of the clusterization free energies for arbitrary clusters is developed and applied to obtain the estimate of the Gibbs clusterization energy for infinitely large clusters.
在量子化学PM3近似框架下，计算了组成式为C(n)F(2)(n + 1)CH(2)CH(2)OH的氟代链烷醇单体（n = 1 - 14, 34）、二聚体（n = 1 - 14, 34）以及三聚体和四聚体（n = 1 - 8）的几何结构和热力学函数特征。结果表明，与具有扁平锯齿形结构的脂肪醇不同，氟代链烷醇单体呈螺旋状，平均主链扭转角为162度。对于二聚体的最低能量结构，观察到分子在二聚体中的自组织现象；这导致形成二聚体的两个分子中对应匹配原子的扭转角呈相反交替。这使得二聚体最稳定的构象为双螺旋。通过对C(34)F(69)CH(2)CH(2)OH二聚体的计算确定了双螺旋的螺距（39.5 Å）和直径（7.3 Å）。聚类焓、熵和吉布斯自由能显示出与氟化链长度呈线性相关。通过对这些热力学量的分析得出结论，当烃链节数超过6时，氟代链烷醇在空气/水界面发生二聚，而对于普通醇类，该特征数为11。这些计算值与实验数据相符。开发了一种用于评估任意簇聚类自由能的加和方案，并将其应用于获得无限大簇的吉布斯聚类能估计值。
