Wang Feng, Wang Yan, Polavarapu Prasad L, Li Tingyu, Drabowicz Józef, Pietrusiewicz K Michal, Zygo Krystyna
Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, USA.
J Org Chem. 2002 Sep 6;67(18):6539-41. doi: 10.1021/jo025908h.
The enantiomers of tert-butyl-1-(2-methylnaphthyl)phosphine oxide 1 have been separated using a homemade HPLC column and an analytical gradient system. Vibrational absorption and circular dichroism spectra for both enantiomers have been measured in CD2Cl2 and CH2Cl2 solutions in the 2000-900 cm(-1) region. The fully relaxed potential energy surface of (S)-tert-butyl-1-(2-methylnaphthyl)phosphine oxide, obtained using the B3LYP functional with a 6-31G basis set, indicated two stable conformers with their populations in a approximately 2:1 ratio. The vibrational absorption and VCD spectra are predicted for these two conformers using the B3LYP functional with a 6-31G basis set. The comparison of predicted and experimental spectra indicated that (+)-tert-butyl-1-(2-methylnaphthyl)phosphine oxide is in the (S)-configuration. This assignment is supported by the ab initio prediction of positive optical rotation for the most stable conformer with an (S)-configuration and the nonequivalence sense of the tert-butyl group chemical shift observed in the 1H NMR spectrum of this enantiomer measured in the presence of (+)-(S)-mandelic acid as a chiral solvating agent.
使用自制的高效液相色谱柱和分析梯度系统分离了叔丁基-1-(2-甲基萘基)氧化膦1的对映体。在CD2Cl2和CH2Cl2溶液中，于2000 - 900 cm(-1)区域测量了两种对映体的振动吸收光谱和圆二色光谱。使用B3LYP泛函和6 - 31G基组得到的(S)-叔丁基-1-(2-甲基萘基)氧化膦的完全弛豫势能面表明，存在两种稳定构象体，其丰度比约为2:1。使用B3LYP泛函和6 - 31G基组预测了这两种构象体的振动吸收光谱和振动圆二色光谱。预测光谱与实验光谱的比较表明，(+)-叔丁基-1-(2-甲基萘基)氧化膦为(S)-构型。在手性溶剂化剂(+)-(S)-扁桃酸存在下测得的该对映体的1H NMR谱中，(S)-构型最稳定构象体的正旋光性的从头算预测以及叔丁基化学位移的不等价性支持了这一归属。
