Sturdy Yvette K, Clary David C
Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford, UK.
Phys Chem Chem Phys. 2007 May 7;9(17):2065-74. doi: 10.1039/b615660f. Epub 2007 Jan 17.
In this paper we calculate the relative conformer populations of the tryptamine molecule. Our approach combines high level electronic structure conformer energies with harmonic frequencies and an anharmonic treatment of the torsional motions using the torsional path integral Monte Carlo method. We have developed a 3-D potential energy surface as a function of the torsional coordinates at the B3LYP/6-31+G(d) level using 2535 grid points. Eight conformers of tryptamine were found to be significantly populated at 430 K as opposed to the experimental observation of seven. This, along with further comparisons with various experimental data, leads us to suppose that conformer interconversion occurs during the cooling phases of many of the experiments. The ordering of the calculated populations fits well with available experimental data. Torsional anharmonicity is found to affect conformer populations more significantly at 430 K than at 100 K (although overall the effects are small), while quantum mechanical effects are not important at either temperature.
在本文中，我们计算了色胺分子的相对构象体丰度。我们的方法将高水平的电子结构构象体能量与谐波频率相结合，并使用扭转路径积分蒙特卡罗方法对扭转运动进行非谐处理。我们在B3LYP/6 - 31 + G(d)水平上，利用2535个网格点，开发了一个作为扭转坐标函数的三维势能面。结果发现，在430 K时，色胺有八个构象体的丰度显著，而实验观察到的是七个。这一点，再加上与各种实验数据的进一步比较，使我们推测在许多实验的冷却阶段会发生构象体的相互转化。计算得到的丰度排序与现有的实验数据吻合得很好。结果发现，在430 K时，扭转非谐性对构象体丰度的影响比在100 K时更为显著（尽管总体影响较小），而在这两个温度下，量子力学效应都不重要。
