Ring Current Effects in Crystals. Evidence from 13C Chemical Shift Tensors for Intermolecular Shielding in 4,7-Di-t-butylacenaphthene versus 4,7-Di-t-butylacenaphthylen
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- 作者：Zhiru Ma ; Merrill D. Halling ; Mark S. Solum ; James K. Harper ; Anita M. Orendt ; Julio C. Facelli ; Ronald J. Pugmire ; David M. Grant ; Aaron W. Amick ; Lawrence T. Scott
- 刊名：Journal of Physical Chemistry A
- 出版年：2007
- 出版时间：March 15, 2007
- 年：2007
- 卷：111
- 期：10
- 页码：2020 - 2027
- 全文大小：180K
- 年卷期：v.111,no.10(March 15, 2007)
- ISSN：1520-5215
文摘
13C chemical shift tensor data from 2D FIREMAT spectra are reported for 4,7-di-t-butylacenaphthene and4,7-di-t-butylacenaphthylene. In addition, calculations of the chemical shielding tensors were completed atthe B3LYP/6-311G** level of theory. While the experimental tensor data on 4,7-di-t-butylacenaphthyleneare in agreement with theory and with previous data on polycyclic aromatic hydrocarbons, the experimentaland theoretical data on 4,7-di-t-butylacenaphthene lack agreement. Instead, larger than usual differences areobserved between the experimental chemical shift components and the chemical shielding tensor componentscalculated on a single molecule of 4,7-di-t-butylacenaphthene, with a root mean square (rms) error of ±7.0ppm. The greatest deviation is concentrated in the component perpendicular to the aromatic plane, with thelargest value being a 23 ppm difference between experiment and theory for the 13CH2 carbon 
delta.gif" BORDER=0 >11 component.These differences are attributed to an intermolecular chemical shift that arises from the graphitelike, stackedarrangement of molecules found in the crystal structure of 4,7-di-t-butylacenaphthene. This conclusion issupported by a calculation on a trimer of molecules, which improves the agreement between experiment andtheory for this component by 14 ppm and reduces the overall rms error between experiment and theory to 4.0ppm. This intermolecular effect may be modeled with the use of nuclei independent chemical shieldings(NICS) calculations and is also observed in the isotropic 1H chemical shift of the CH2 protons as a 4.2 ppmdifference between the solution value and the solid-state chemical shift measured via a 13C-1H heteronuclearcorrelation experiment.
delta.gif" BORDER=0 >11 component.These differences are attributed to an intermolecular chemical shift that arises from the graphitelike, stackedarrangement of molecules found in the crystal structure of 4,7-di-t-butylacenaphthene. This conclusion issupported by a calculation on a trimer of molecules, which improves the agreement between experiment andtheory for this component by 14 ppm and reduces the overall rms error between experiment and theory to 4.0ppm. This intermolecular effect may be modeled with the use of nuclei independent chemical shieldings(NICS) calculations and is also observed in the isotropic 1H chemical shift of the CH2 protons as a 4.2 ppmdifference between the solution value and the solid-state chemical shift measured via a 13C-1H heteronuclearcorrelation experiment.