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Synthesis, X-ray crystallographic, and dynamic 1H NMR studies of crown-tetrathia[3.3.3.3]metacyclophanes—conformational control by cooperative intramolecular C–H⋯π interaction both in solid state and in solution
- Source :
-
Tetrahedron . Sep2005, Vol. 61 Issue 39, p9248-9256. 9p. - Publication Year :
- 2005
-
Abstract
- Abstract: Crown-tetrathia[3.3.3.3]metacyclophanes 3a–c were synthesized via intermolcular coupling reaction in 22–30% yields. X-ray crystal analysis of 3b revealed that it adopted a perpendicular conformation ( 3b-B or 3b-C ) in which two aromatic rings were inclined to be perpendicular to the opposite aromatic rings, driving two internal methyl groups into the π-cloud of the corresponding benzene rings. Furthermore, this perpendicular structural feature led to benzylic protons of thia-bridges being in close proximity to the adjacent aromatic rings. As a result, the induced upfield shifts for the two internal methyl protons and four benzylic protons were clearly observed in dynamic 1H NMR spectra at low temperature, indicating that the intramolecular C–H⋯π interaction became increasingly important at low temperature. The energy barrier for inter-conversion between 3b-B and 3b-C was estimated to be 12.1kcalmol−1 by using a coalescence method. The total stabilization enthalpy of the C–H⋯π interactions was quantitatively calculated to be 7.9±0.8kcalmol−1 by the dynamic NMR spectroscopy. In contrast, 3a showed two non-interconvertible conformers at room temperature, which tended to interconvert at elevated temperature, however, many conformers co-existed at low temperature. [Copyright &y& Elsevier]
Details
- Language :
- English
- ISSN :
- 00404020
- Volume :
- 61
- Issue :
- 39
- Database :
- Academic Search Index
- Journal :
- Tetrahedron
- Publication Type :
- Academic Journal
- Accession number :
- 18242549
- Full Text :
- https://doi.org/10.1016/j.tet.2005.07.071