LOW-TEMPERATURE C-13 MAGNETIC-RESONANCE IN SOLIDS .3. LINEAR AND PSEUDOLINEAR MOLECULES
LOW-TEMPERATURE C-13 MAGNETIC-RESONANCE IN SOLIDS .3. LINEAR AND PSEUDOLINEAR MOLECULES
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DOI：
10.1021/ja00337a003
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发表时间：
1984-01-01
影响因子：
15
通讯作者：
KUTZELNIGG, W
中科院分区：
文献类型：
--
作者：
BEELER, AJ;ORENDT, AM;KUTZELNIGG, W
本文测定了五种线性分子（CO、CO_2、OCS、C_30_2、乙炔）和四种假线性分子（丙炔、2-丁炔、丙烯、乙烯酮）的固体低温~（13）C NMR谱。屏蔽张量轴的分配是由对称性，但在所有alieneandketene。在这些伪线性分子移位分配的基础上从头计算的IGLO版本的耦合Hartree-Fock方法。除一氧化碳外，Cn的化学位移张量的平行分量（，，）在Me 4Si的-90 ppm处显著恒定，为讨论顺磁屏蔽项建立了参考点。两个品种的抗磁项和偏离中心的屏蔽条款的变化被发现是相对较小的。在氢偏离伪线性分子的CC轴的分子中，C n对称性的破坏导致张量屏蔽的重大位移。理论相关性的相对实验屏蔽值是非常好的，虽然在低场范围内的幅度的协议，作为一个移动远离甲烷位移，这是用来作为一个基准值，以建立比较。它的结论是，该理论忠实地代表了屏蔽现象，并可用于分配屏蔽组件到特定的空间取向时，对称性功能或其他明确的信息是缺乏的。
The solid-state low-temperature 13C NMR spectra of five linear (CO, C02, OCS, C302, acetylene) and four pseudolinear (propyne, 2-butyne, aliene, ketene) molecules havebeen obtained. The assignments of the shielding tensor axes are made from symmetry in all but alieneand ketene. In these pseudolinear molecules shift assignments are based on ab initio calculations by the IGLO version of the coupled Hartree-Fock method. Except for carbon monoxide, the parallel component of the chemical shift tensor (,,) for C „is remarkably constant at-90 ppm from Me4Si, establishing a reference pointfor discussing the paramagnetic shielding terms. Variations in both the diamagnetic term and off-center shielding terms of both varieties were found to be relatively small. Destruction of the C „symmetry in molecules having hydrogen lying off the CC axis of pseudolinear molecules resulted in major shifts in the tensorial shieldings. Theoretical correlationof the relative experimental shielding values is very good although the agreement of magnitudes in the low-field range worsens as one moves away from the methane shift which is used as a fiducial value to establish the comparison. It is concluded that the theory faithfully represents the shielding phenomena and may be used to assign shielding components to specificspatial orientations when symmetry features or other unequivocal information is lacking.