Polavarapu Prasad L, Jeirath Neha, Walia Sheena
Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, USA.
J Phys Chem A. 2009 May 7;113(18):5423-31. doi: 10.1021/jp811055y.
The experimental vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotatory dispersion (ORD) spectra for both enantiomers of 6,6'-dibromo-1,1'-bi-2-naphthol have been measured. The corresponding quantum chemical predictions for three different orientations of hydroxyl groups in this molecule were obtained using 6-31G*, 6-311G(2d,2p) and 6-311++G(2d,2p) basis sets and the B3LYP density functional. The absolute configuration inferred by comparing the predicted spectra with experimental data is the same in VCD, ECD, and ORD methods, but spectral sensitivity to conformation varies among these methods. It is found that predicted ECD in the 200-350 nm region does not change significantly for the three conformers. As a result, the sensitivity of ECD to the conformation of hydroxyl groups in 6,6'-dibromo-1,1'-bi-2-naphthol is rather limited. Similarly, a comparison between experimental and predicted ORD spectra indicated that ORD spectral prediction is not the best method of choice for discrimination among different conformations of O-H groups. On the other hand, the predicted VCD, and associated absorption, spectral patterns in the 1600-900 cm(-1) region are found to change significantly for the three conformations, and the experimental spectra correlate well with those predicted for only one conformation. These observations suggest that, among the three chiroptical spectroscopic methods investigated, VCD provides better sensitivity to the conformation of hydroxyl groups. The use of PCM model for exploring the influence of CH(2)Cl(2) solvent on vibrational spectra indicated that this model is not appropriate for modeling the CH(2)Cl(2) solvent influence on the vibrational absorption and VCD spectra of 6,6'-dibromo-1,1'-bi-2-naphthol.
已测量了6,6'-二溴-1,1'-联-2-萘酚两种对映体的实验振动圆二色性（VCD）、电子圆二色性（ECD）和旋光色散（ORD）光谱。使用6-31G*、6-311G(2d,2p)和6-311++G(2d,2p)基组以及B3LYP密度泛函，获得了该分子中羟基三种不同取向的相应量子化学预测结果。通过将预测光谱与实验数据进行比较推断出的绝对构型在VCD、ECD和ORD方法中是相同的，但这些方法对构象的光谱敏感性各不相同。研究发现，对于三种构象，200 - 350 nm区域内预测的ECD变化不显著。因此，ECD对6,6'-二溴-1,1'-联-2-萘酚中羟基构象的敏感性相当有限。同样，实验ORD光谱与预测ORD光谱的比较表明，ORD光谱预测并非区分O - H基团不同构象的最佳选择方法。另一方面，发现1600 - 900 cm(-1)区域内预测的VCD以及相关的吸收光谱模式对于三种构象有显著变化，并且实验光谱与仅针对一种构象预测的光谱相关性良好。这些观察结果表明，在所研究的三种手性光谱方法中，VCD对羟基构象具有更好的敏感性。使用PCM模型探究CH(2)Cl(2)溶剂对振动光谱的影响表明，该模型不适用于模拟CH(2)Cl(2)溶剂对6,6'-二溴-1,1'-联-2-萘酚振动吸收和VCD光谱的影响。
