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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Accurate Determination of the Deformation of the Benzene Ring upon Substitution: Equilibrium Structures of Benzonitrile and Phenylacetylene
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Accurate Determination of the Deformation of the Benzene Ring upon Substitution: Equilibrium Structures of Benzonitrile and Phenylacetylene

机译：取代后苯环变形的准确测定：苯甲腈和苯乙炔的平衡结构

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摘要

Accurate equilibrium, r_e, structures of the monosubstituted benzene molecules benzonitrile, C_6H_5CN, and phenylacetylene, C6H5CCH, have been determined using two different, to some extent complementary techniques. The semiexperimental, r_e~(SE), structural parameters are the result of a least-squares fit to equilibrium rotational constants derived from experimental effective ground-state rotational constants and rovibrational corrections based principally on an ab initio cubic force field. The composite ab initio Born?Oppenheimer, r_e~(BO), structural parameters are obtained from frozen-core and all-electron MP2 and the CCSD(T) geometry optimizations using Gaussian basis sets up to quintuple-zeta quality. The DFT(B3LYP) method, with two different Gaussian basis sets, 6- 31G~* and 6-311+G(3df,2pd), was used to calculate the cubic force field employed during the r_e~(SE) structure determination. With the 6-31G~* basis set, the error of the rovibrational correction is to a large extent random, whereas with the 6-311+G(3df,2pd) basis set it is mainly systematic. As shown here, systematic errors do not have a significant effect on the accuracy of the derived structure; the quality of the structural fit, however, is sensitive to the true accuracy of the ground-state rotational constants. An even more important general conclusion of this study is that the addition of extra rotational constants from multisubstituted species does not seem to improve the accuracy of the r_e~(SE) structures, quite in contrast to the highly desirable availability of data corresponding to all singly substituted species.
机译：已使用两种不同的，在某种程度上互补的技术确定了单取代苯分子苄腈C_6H_5CN和苯乙炔C6H5CCH的准确平衡r_e结构。半实验结构参数r_e〜（SE）是对平衡旋转常数进行最小二乘拟合的结果，该平衡旋转常数是从实验有效基态旋转常数和主要基于从头算立方力场进行的振动校正得出的。复合的从头算Born？Oppenheimer，r_e〜（BO），结构参数是从冻结核和全电子MP2以及CCSD（T）几何优化使用高斯基础集获得的，其质量达到五倍。使用DFT（B3LYP）方法，使用两个不同的高斯基集6-31G〜*和6-311 + G（3df，2pd），来计算确定r_e〜（SE）结构时使用的立方力场。对于6-31G〜*基集，旋转校正的误差在很大程度上是随机的，而对于6-311 + G（3df，2pd）基集，误差主要是系统的。如此处所示，系统误差不会对派生结构的准确性产生重大影响。但是，结构配合的质量对基态旋转常数的真实精度很敏感。这项研究的一个甚至更重要的一般结论是，与高度可取的分别对应所有数据的可用性相反，来自多取代物种的额外旋转常数似乎并未提高r_e〜（SE）结构的准确性。替代物种。

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