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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Isomer Identification for Fullerene C_(84) by ~(13)C NMR Spectrum: A Density-Functional Theory Study
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Isomer Identification for Fullerene C_(84) by ~(13)C NMR Spectrum: A Density-Functional Theory Study

机译：〜（13）C NMR光谱鉴定富勒烯C_（84）的异构体：密度泛函理论研究

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摘要

Optimized geometries of all 24 isolated pentagon rule (IPR) abiding isomers of fullerene C_(84) have been calculated using density-functional theory (DFT) at the B3LYP/6-31G~* level. ~(13)C NMR chemical shieldings are obtained employing the gauge-independent atomic orbital method. The calculated chemical shifts are in good agreement with experimental values for isomers 4, 22, and 23, all of which have been experimentally assigned without ambiguity. The previously NMR spectra allow us to confirm earlier assignment and validate the DFT approach. The previously temporarily assigned isomers D_2(II), C_2, C_s(a), and C_s(b) are isomers 5, 11, 16, and 14, respectively. Discrepancies exist between the experimental and theoretical NMR spectra for isomers 19 and 24. The predicted NMR spectra for other isomers are also presented. The local geometry is determined largely by connectivity. The relationship between the chemical shift and the π-orbital axis vector (POAV) angle is far from linear, although the chemical shift generally increases when the POAV angle increases. The pyrene-type carbons form five distinct groups in the chemical shift vs POAV angle graph according to the local connectivity, providing a usable tool for their identification. Similarly, two and three groups can be identified for corannulene and pyracylene types of carbons, but these are not sufficiently distinct to be useful.
机译：使用密度泛函理论（DFT）在B3LYP / 6-31G〜*水平上计算了富勒烯C_（84）的所有24个独立的五边形规则（IPR）遵守的异构体的最佳几何形状。采用不依赖于轨距的原子轨道方法获得了〜（13）C NMR化学屏蔽。所计算的化学位移与异构体4、22和23的实验值高度吻合，所有这些均已通过实验明确指定。先前的NMR光谱使我们能够确认较早的分配并验证DFT方法。先前临时分配的异构体D_2（II），C_2，C_s（a）和C_s（b）分别为异构体5、11、16和14。异构体19和24的实验NMR光谱和理论NMR光谱之间存在差异。还介绍了其他异构体的预测NMR光谱。局部几何形状主要由连接性决定。尽管化学位移通常随POAV角增加而增加，但化学位移与π轨道轴矢量（POAV）角之间的关系远非线性。 the型碳根据局部连通性在化学位移与POAV角度图中形成五个不同的基团，为鉴定它们提供了有用的工具。类似地，可以鉴定出两个和三个基团用于cor喃和pyr基类型的碳，但是它们之间的区别并不足够大。

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