Conformational cooling dynamics in matrix-isolated 1,3-butanediol.
Conformational cooling dynamics in matrix-isolated 1,3-butanediol.
复制标题
基质隔离的 1,3-丁二醇的构象冷却动力学。
DOI：
--
复制
发表时间：
2009
影响因子：
2.9
通讯作者：
J. S. Redinha
中科院分区：
文献类型：
--
作者：
Mário T. S. Rosado;A. J. L. Jesus;I. Reva;R. Fausto;J. S. Redinha
从理论上表征了单体1,3-丁二醇的完整构象空间，并在MP2/6-311++G(d,p)水平上发现了73个独特的稳定构象异构体。它们被分为九个家族，其成员具有相同的重原子主链结构，但氢原子方向不同。第一和第三最多的主链家族由分子内氢键的形成控制；然而，第二个排除了这种类型的相互作用，并且在以前的研究中经常被忽视。它的稳定性是由其主要构象异构体相对较高的熵决定的。四种最重要的构象异构体的氢键通过分子中的原子（AIM，也称为 QTAIM）和自然键轨道（NBO）分析来表征。使用适当的等糖反应，发现氢键能稳定在 12-14 kJ mol(-1) 。实验上，在低温惰性基质中分离出1,3-丁二醇单体分子，并从构象分布的角度分析了它们的红外光谱。构象互变反应路径的所有相关过渡态都在同一理论水平上进行表征，以解释在低温基质中观察到的构象冷却动力学。经计算，OH 基团旋转的能垒非常低（<3 kJ mol(-1)）。这些障碍在 10 K（Ar 基质）下的实验中在基质沉积过程中被克服，并且每个家族内的种群被减少到最稳定的构象异构体。基底温度的进一步升高（高达40 K，Xe基质）导致构象冷却，其中可以克服中等高度屏障（大约13 kJ mol(-1)）并且所有构象群转化为地面构象状态。值得注意的是，这种状态由最稳定的氢键族的两种形式组成，通过计算预测它们会意外简并，并在退火基体中发现等量。所有这些实验观察到的构象冷却过程都经过分析并得到与理论计算完全一致的支持。
The complete conformational space of monomeric 1,3-butanediol has been characterized theoretically, and 73 unique stable conformers were found at the MP2/6-311++G(d,p) level. These were classified into nine families whose members share the same heavy atom backbone configurations and differ in the hydrogen atom orientations. The first and third most populated backbone families are governed by the formation of an intramolecular hydrogen bond; however, the second precludes this type of interaction and was frequently overlooked in previous studies. Its stability is determined by the relatively high entropy of its main conformers. The hydrogen bonding of four of the most important conformers was characterized by means of atoms in molecules (AIM, also known as QTAIM) and natural bond orbital (NBO) analyses. Using appropriate isodesmic reactions, hydrogen bonding energy stabilizations of 12-14 kJ mol(-1) have been found. Experimentally, monomeric molecules of 1,3-butanediol were isolated in low-temperature inert matrixes, and their infrared spectra were analyzed from the viewpoint of the conformational distribution. All the relevant transition states for the conformational interconversion reaction paths were characterized at the same level of theory to interpret the conformational cooling dynamics observed in the low-temperature matrixes. The energy barriers for rotation of the OH groups were calculated to be very low (<3 kJ mol(-1)). These barriers were overcome in the experiments at 10 K (Ar matrix), in the process of matrix deposition, and population within each family was reduced to the most stable conformers. Further increase in the substrate temperature (up to 40 K, Xe matrix) resulted in conformational cooling where the medium-height barriers (approximately 13 kJ mol(-1)) could be surmounted and all conformational population converted to the ground conformational state. Remarkably, this state turned to consist of two forms of the most stable hydrogen bonded family, which were predicted by calculations to be accidentally degenerated and were found in the annealed matrix in equal amounts. All of these experimentally observed conformational cooling processes were analyzed and supported by full agreement with the theoretical calculations.