Konformation und Dynamik von [6]Paracyclophan-8,9-dicarbonsäure-dimethylester. Eine 1H- und 13C-NMR Studie

✍ Scribed by Harald Günther; Peter Schmitt; Hartmut Fischer; Werner Tochtermann; Jörg Liebe; Christian Wolff

• Publisher: John Wiley and Sons
• Year: 1985
• Tongue: German
• Weight: 757 KB
• Volume: 68
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19850680330

✦ Synopsis

Conformation and Dynamics of Dimethyl [6]Paracyclophane‐8,9‐dicarboxylate. A ^1^H‐ and ^13^C‐NMR Study

The ^1^H‐ und ^13^C‐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 ^1^H, ^1^H 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 ^1^H‐NMR shielding properties of the boat‐shaped benzene ring were detected. The ^13^C 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 Δ__H__^≠^ = 43.25 ± 0.72 kJ/mol, Δ__S__^≠^ = −51.27 ± 2.66 J/K mol, and Δ__G__^≠^(298) = 58.53 kJ/mol for the dynamic process corresponding to an inversion of the methylene bridge.