ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Conformation and Dynamics of Dimethyl [6]Paracyclophane-8,9-dicarboxylate. A 1H- and 13C-NMR StudyThe 1H- und 13C-NMR spectra of dimethyl [6]paracyclophane-8,9-dicarboxylate have been assigned and analyzed in the slow-exchange limit (-20°C) for the ring-inversion process of the methylene bridge using several 2D-NMR techniques. The vicinal 1H, 1H coupling constants of the methylene chain show a Karplus-type dependence on torsional angles. The observed values indicate that the solution conformation of 1 closely resembles that found in the crystal. No significant changes in the 1H-NMR shielding properties of the boat-shaped benzene ring were detected. The 13C chemical shifts of the methylene C-atoms can be explained without invoking ring current contributions, which are too small for unambiguous identification. A lineshape analysis for the AB⇌BA exchange system of the aromatic protons yielded ΔH≠ = 43.25 ± 0.72 kJ/mol, ΔS≠ = -51.27 ± 2.66 J/K mol, and ΔG≠(298) = 58.53 kJ/mol for the dynamic process corresponding to an inversion of the methylene bridge.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19850680330
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