Dynamics in Host–Guest Complexes of Molecular Tweezers and Clips
| Autor: | Viola Podsadlowski, Uta P. Buchele, Frank-Gerrit Klärner, Heinz Bandmann, Ulrich Burkert, Matthias Lobert |
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| Rok vydání: | 2006 |
| Předmět: |
Stereochemistry
Organic Chemistry Chemie Supramolecular chemistry General Chemistry Nuclear magnetic resonance spectroscopy Catalysis Dissociation (chemistry) chemistry.chemical_compound Crystallography symbols.namesake Tropylium tetrafluoroborate Molecular recognition chemistry symbols van der Waals force Molecular tweezers Conformational isomerism |
| Zdroj: | Chemistry - A European Journal. 12:1629-1641 |
| ISSN: | 1521-3765 0947-6539 |
| DOI: | 10.1002/chem.200500902 |
| Popis: | The dynamics in the host-guest complexes of the molecular tweezers 1 a,b and clips 2 a,b with 1,2,4,5-tetracyanobenzene (TCNB, 3) and tropylium tetrafluoroborate (4) as guest molecules were analyzed by temperature-dependent 1H NMR spectroscopy. The TCNB complexes of tweezers 1 a,b were found to be particularly stable (dissociation barrier: DeltaG(++)=16.8 and 15.7 kcal mol(-1), respectively), more stable than the TCNB complexes of clips 2 a,b and the tropylium complex of tweezer 1 b (dissociation barrier: DeltaG(++)=12.4, 11.2, and 12.3 kcal mol(-1), respectively). A detailed analysis of the kinetic and thermodynamic data (especially the negative entropies of activation found for complex dissociation) suggests that in the transition state of dissociation the guest molecule is still clipped between the aromatic tips of the host molecule. The 1H NMR analysis of the TCNB complexes 3@1 b and 3@2 a at low temperatures (T |
| Databáze: | OpenAIRE |
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