TD-DFT Analysis of the Dissymmetry Factor in Camphor

The fact that the dissymmetry lgeb (g-factor) of camphor is large has been known for decades, and the interpretation of the observed data has also been known for a long time. However, due to the ability of quantum chemical methods to describe chiroptical phenomena more appropriately, additional approaches based on these methods have been successful employed. The g-factor lgebra in S-camphor and L-tryptophan have been investigated by UV-Vis and electronic circular dichroism (ECD) spectroscopies of the n ® p* electronic transition. Time-dependent density functional theory (TD-DFT) calculations at CAM-B3LYP/6-311++G(3df,2p)//B3LYP/6-311++G(2d,p) level of theory including Grimme’s dispersion effects have been performed. The lgebra effect was added using solvation model based on density (SMD) approach in solvation environment. The results permit insights into the ground and excited states electronic properties associated with the g-factor. The theoretical spectra showed good similarity with the experimental ones. The theoretical ECD of camphor was found at 282 nm, whereas the experimental shows its maximum at 290 nm. Regarding the maximum value of the molar absorptivity lgebrante, the theoretical and experimental values were 16.2 and 30.2 M-1 cm-1, respectively. The same concordance was obtained for g-factor, as follows: -0.0445 and -0.0886, for experimental and theoretical results, respectively.

数十年来，人们早已知晓樟脑的不对称g因子数值较大，且对相关观测数据的诠释也早有定论。不过，得益于量子化学方法可更精准地描述手性光学现象，基于此类方法的衍生研究手段已成功得以应用。
针对S-樟脑与L-色氨酸的g因子，研究者通过n→π*电子跃迁的紫外-可见光谱（UV-Vis）与电子圆二色光谱（electronic circular dichroism, ECD）展开了相关研究。本研究采用含时密度泛函理论（Time-dependent density functional theory, TD-DFT），在CAM-B3LYP/6-311++G(3df,2p)//B3LYP/6-311++G(2d,p)理论级别下开展计算，并纳入了格里姆（Grimme）色散校正效应。在溶剂化环境中，通过基于密度的溶剂化模型（solvation model based on density, SMD）引入了溶剂化效应。
研究结果可为与g因子相关的基态与激发态电子性质提供深入见解。理论光谱与实验光谱展现出良好的一致性：理论计算得到的樟脑电子圆二色光谱峰值位于282 nm，而实验观测的峰值则为290 nm。就摩尔消光系数的峰值而言，理论计算值与实验观测值分别为16.2 M⁻¹·cm⁻¹与30.2 M⁻¹·cm⁻¹。对于g因子的数值，二者同样具有较好的一致性：实验结果为-0.0445，理论结果为-0.0886。