Thomas Laura L, Christakis Theodore J, Jorgensen William L
Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520-8107, USA.
J Phys Chem B. 2006 Oct 26;110(42):21198-204. doi: 10.1021/jp064811m.
Monte Carlo (MC) statistical mechanics simulations have been carried out for the homologous alkane series of n-butane through n-dodecane in the gas phase and for the pure liquids at 298 K and 1 atm using the OPLS-AA force field. The study addresses potential cumulative deviations of computed properties and potential conformational differences between the gas phase and pure liquids, for example, from self-solvation in the gas phase. The average errors in comparison with experimental data for the computed densities and heats of vaporization are modest at 0.7% and 6.9%, respectively. Also, the invariant gas and liquid-phase results for average end-to-end distances and percentages of trans conformations for each nonterminal C-C bond assert that the conformer populations are not altered upon transfer from the gas phase to the pure liquid for the n-alkanes in this size range. Average end-to-end distances were also computed from the results of conformational searches and corroborated the MC findings. Quantitatively, the OPLS-AA result for the trans population of the C3-C4 bond in n-undecane is in close agreement with the findings from (13)C NMR experiments. Finally, previous work on determining the shortest n-alkane that does not have an all-trans global energy minimum has been extended. The smallest n-alkane with a hairpin geometry that is lower in energy than the all-trans conformer occurs for C(22)H(46) with OPLS-AA, though with a correction for GG sequences, the true turning point is likely in the C(16)-C(18) range.
使用OPLS - AA力场，对正丁烷至正十二烷的同系烷烃系列在气相中以及在298 K和1个大气压下的纯液体进行了蒙特卡罗（MC）统计力学模拟。该研究探讨了计算性质的潜在累积偏差以及气相和纯液体之间潜在的构象差异，例如气相中的自溶剂化导致的差异。与计算密度和汽化热的实验数据相比，平均误差分别为0.7%和6.9%，较为适中。此外，对于每个非末端C - C键的平均端到端距离和反式构象百分比，气相和液相的结果不变，这表明对于该尺寸范围内的正构烷烃，从气相转移到纯液体时构象群体没有改变。还从构象搜索结果计算了平均端到端距离，并证实了MC的结果。定量地说，OPLS - AA计算的正十一烷中C3 - C4键反式群体的结果与碳 - 13核磁共振实验的结果非常一致。最后，先前关于确定没有全反式全局能量最小值的最短正构烷烃的工作得到了扩展。对于C(22)H(46)，使用OPLS - AA时出现了能量低于全反式构象的发夹几何形状的最小正构烷烃，不过对于GG序列进行校正后，真正的转折点可能在C(16) - C(18)范围内。
