Premium
Konformation und Dynamik von [6]Paracyclophan‐8,9‐dicarbonsäure‐dimethylester. Eine 1 H‐ und 13 C‐NMR Studie
Author(s) -
Günther Harald,
Schmitt Peter,
Fischer Hartmut,
Tochtermann Werner,
Liebe Jörg,
Wolff Christian
Publication year - 1985
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19850680330
Subject(s) - chemistry , ring flip , methylene , ring (chemistry) , nmr spectra database , vicinal , coupling constant , chemical shift , crystallography , methylene bridge , proton nmr , nuclear magnetic resonance spectroscopy , benzene , stereochemistry , computational chemistry , spectral line , medicinal chemistry , organic chemistry , physics , particle physics , astronomy
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.