Carbon 13 chemical shift tensors in aromatic compounds. 3. Phenanthrene and triphenylene

Journal Article · Wed Apr 08 04:00:00 EDT 1992 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja00034a011· OSTI ID:236332

Soderquist, A; Hughes, C D; Horton, W J; Facelli, J C; Grant, D M ^[1]

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1. Univ. of Utah, Salt Lake City, UT (United States)

Measurements of the principal values of the {sup 13}C chemical shift tensor are presented for the three carbons in triphenylene and for three different {alpha} carbons in phenanthrene. The measurements in triphenylene were made in natural abundance samples at room temperature, while the phenanthrene tensors were obtained from selectively labeled compounds (99% {sup 13}C) at low temperatures ({approx} 25 K). The principal values of the shift tensors were oriented in the molecular frame using ab initio LORG calculations. The steric compression at C{sub 4} in phenanthrene and in corresponding positions in triphenylene is manifested in sizable upfield shift in the {sigma} 33 component relative to the corresponding {sigma} 33 values at C{sub 1} and C{sub 9} in phenanthrene. The upfield shift in {sigma} 33 is mainly responsible for the well-known upfield shift of the isotropic chemical shifts of such sterically perturbed carbons. In phenanthrene c{sub 9} exhibits a unique {sigma} 22 value reflecting the greater localization of {pi}-electrons in the c{sub 9}-C{sub 10} bond. This localization of the {pi}-electrons at the C{sub 9}-C{sub 10} bond in the central ring of phenanthrene also corresponds with the most likely ordering of electrons described by the various Kekule structures in phenanthrene. The analysis of the {sup 13}C chemical shieldings of the bridgehead carbons in the triphenylene provides significant experimental information on bonding between rings in polycyclic aromatic compounds. 39 refs., 8 fig., 3 tab.

• Sponsoring Organization: USDOE
• OSTI ID: 236332
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 8 Vol. 114; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
CARBON 13
CHEMICAL SHIFT
LABELLED COMPOUNDS
MATHEMATICAL MODELS
NUCLEAR MAGNETIC RESONANCE
PHENANTHRENE
TRIPHENYLENE