Abstract
The conformations and dynamic processes in a series of relatively unstrained [2 4]paracyclophanes (with one, two or four -CH 2-CH 2-bridges) and some closely related compounds have been analysed. Their 1NMR spectra have been recorded at low temperatures and the temperature dependence rationalised as being due to essentially two types of dynamic process-the torsional motion around the sp 3-sp 3 C-C bonds in the bridges, and the rotation around the sp 2-sp 3 C-C bonds adjacent to the benzene rings. The barriers to the former process are similar for the series of cyclophanes 1–6 and are due to steric and electronic interactions in the syn-oriented transition states. In cyclophanes 7–9, in which anti-orientations of the aromatic rings are possible, the barriers are lower. The latter process, involving the rotation of the benzene rings, becomes important at temperatures below 150 K and has not been further analysed.
Published Version
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