Cluster Analysis of ¹³C Chemical Shift Tensor Principal Values in Polycyclic Aromatic Hydrocarbons

Abstract

This paper presents a hierarchical cluster analysis of the principal values of the 13 C chemical shift tensors encountered in polycyclic aromatic hydrocarbons (PAHs). Because of the limited set of experimental data presently available, the analysis was performed using chemical shifts tensors calculated using the DFT (B3PW91) GIAO method with a D95 basis set on optimized molecular geometries obtained using the CVFF force field and the DISCOVER routine in MSI's InsightII package. The good correlation observed between the calculated and the available experimental values supports the use of calculated values in the analysis. The hierarchical cluster analysis was performed for two data sets of increasing size and the classification was found independent of the size of the sample, leading to the conclusion that the results presented here are valid for the types of PAHs reported. The classification of the tensors using hierarchical cluster analysis produces classes of chemical shift principal values that can be associated with intuitive chemical types of carbons present in PAHs.

Carbon-13 chemical-shift tensors in indigo: A two-dimensional NMR-ROCSA and DFT Study

“…C5, four bonds from the nitrogen site, is the final class. The principal components of the 13 C chemical-shift tensor for C5 fall within the tolerances of polycyclic-aromatic hydrocarbons (PAH) reported by Facelli [50]. However, the remaining carbon sites do not fall within the tolerances provided in Ref.…”

“…However, the remaining carbon sites do not fall within the tolerances provided in Ref. [50], indicating the substantial role of the nitrogen heteroatom on the observed chemical shifts of carbons in the ring.…”

Calculations of chemical shieldings: Theory and applications

“…To this end it is necessary to estimate the number of possible types of distinct NMR chemical shielding signatures that can be present in these materials. We have recently studied this problem in polycyclic aromatic hydrocarbons (PAHs) (77), which are the main component of many high-rank coals and soots. Ideally, this distribution should be obtained from an extensive data base of experimental chemical shielding tensors in PAHs, but the labor-intensive experimental methods used to measure chemical shift tensors or their principal values has severely impaired the development of such a database.…”

“…This is always a nonplanar configuration; VI: bridgehead aromatic carbons attached to three six-membered rings in a planar configuration; and VII: bridgehead aromatic carbons attached to three six-membered rings in a nonplanar configuration. From Facelli et al (77 ).…”

13C chemical-shift anisotropy of alkyl-substituted aromatic carbon in anthracene derivatives

“…However, a single value of 142 ppm has been proposed for spectral deconvolution in kerogen [3] and peat [10]. A hierarchical cluster analysis of 13 C CSA values of PAH molecules suggested two categories for alkyl-substituted aromatic carbon -one centered at 135.3 ppm and a second at 156.7 ppm [16]. Structures with a bicyclic bridge moiety are absent from the cluster analysis.…”