Orientational effect of aryl groups on 77Se NMR chemical shifts: experimental and theoretical investigations.
Orientational effect of aryl groups on 77Se NMR chemical shifts: experimental and theoretical investigations.
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DOI：
10.1002/chem.200500927
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发表时间：
2006-05
期刊：
影响因子：
--
通讯作者：
W. Nakanishi;S. Hayashi;Daisuke Shimizu;M. Hada
中科院分区：
文献类型：
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作者：
W. Nakanishi;S. Hayashi;Daisuke Shimizu;M. Hada
基于实验和理论研究，阐明了p-YC_6 H_4（Ar）对Δ（Se）的取向效应。在ArSeR中的Se-CR处于Ar平面（pl）或垂直于平面（pd）的情况下检查该效果。9-（芳基硒基）蒽（1）和1-（芳基硒基）蒽醌（2）分别用于建立在pl和pd中的效应。如预期的，相对于Y=H，对于Y= NMe 2、OMe和Me观察到大的高场位移，并且对于Y=COOEt、CN和NO2在1中观察到大的低场位移。相对于Y=H，Y= NMe 2、OMe、Me、F、Cl和Br带来大的高场位移，而Y=CN和NO2在2中带来低场位移，Y=COOEt的位移可以忽略不计。基于DFT-GIAO方法，假设pl和pd，计算了ArSeR（R=H，Me和Ph）的Se的绝对磁屏蔽张量（sigma（Se））。观察到的字符很好地解释了总西格玛（硒）。顺磁项（sigmap（Se））由（sigmap（Se）xx+sigmap（Se）yy）支配，其中np（Se）（由4pz（Se）构成）的方向被设置为z轴。pl中的主要相互作用是np（Se）-pi（C_6H_4）-pz（Y）型。在磁场下，通过在pi（SeC 6 H4 Y）和pi*（SeC 6 H4 Y）中的4pz（Se）与在sigma（CSeX）和sigma*（CSeX）（X=H或C）中的4px（Se）和4py（Se）的混合物，发生pl中的Y依赖性。Pd中的主要相互作用是sigma（CSeX）-pi（C6 H4）-px（Y）型，其中Se-X几乎在x轴上。Pd中的Y依赖性主要来自np（Se）中的4pz（Se）与改性的sigma*（CSeX）中的4px（Se）和4py（Se）的混合物，因为np（Se）被电子填充。它表明，无论Y是电子供体或电子受体，Y对sigmap（Se）在pl构象的效果是相同的，而对于pd构象的效果是更大的，当Y是电子供体，如观察到的1和2，分别。计算了每个分子轨道和每个跃迁对sigmap（Se）的贡献，使我们能够清楚地认识和可视化该效应。
The orientational effect of p-YC6H4 (Ar) on delta(Se) is elucidated for ArSeR, based on experimental and theoretical investigations. The effect is examined in the cases in which Se--CR in ArSeR is either in the Ar plane (pl) or is perpendicular to the plane (pd). 9-(Arylselanyl)anthracenes (1) and 1-(arylselanyl)anthraquionones (2) are employed to establish the effect in pl and pd, respectively. Large upfield shifts are observed for Y=NMe2, OMe, and Me, and large downfield shifts for Y=COOEt, CN, and NO2 in 1, relative to Y=H, as is expected. Large upfield shifts are brought by Y=NMe2, OMe, Me, F, Cl, and Br, and downfield shifts by Y=CN and NO2 in 2, relative to Y=H, with a negligible shift by Y=COOEt. Absolute magnetic shielding tensors of Se (sigma(Se)) are calculated for ArSeR (R=H, Me, and Ph), assuming pl and pd, based on the DFT-GIAO method. Observed characters are well explained by the total sigma(Se). Paramagnetic terms (sigmap(Se)) are governed by (sigmap(Se)xx+sigmap(Se)yy), in which the direction of np(Se) (constructed by 4pz(Se)) is set to the z axis. The main interaction in pl is the np(Se)-pi(C6H4)-pz(Y) type. The Y dependence in pl occurs through admixtures of 4pz(Se) in pi(SeC6H4Y) and pi*(SeC6H4Y), modified by the conjugation, with 4px(Se) and 4py(Se) in sigma(CSeX) and sigma*(CSeX) (X=H or C) under a magnetic field. The main interaction in pd is the sigma(CSeX)-pi(C6H4)-px(Y) type, in which Se-X is nearly on the x axis. The Y dependence in pd mainly arises from admixtures of 4pz(Se) in np(Se) with 4px(Se) and 4py(Se) in modified sigma*(CSeX), since np(Se) is filled with electrons. It is demonstrated that the effect of Y on sigmap(Se) in the pl conformation is the same regardless of whether Y is an electron-donor or electron-acceptor, whereas for pd conformations the effect is greater when Y is an electron donor, as observed in 1 and 2, respectively. Contributions of each molecular orbital and each transition on sigmap(Se) are evaluated, which enables us to recognize and visualize the effect clearly.