[5]metacyclophanes a spectroscopic and theoretical investigation of structure and conformation

✍ Scribed by L.A.M. Turkenburg; W.H. de Wolf; F. Bickelhaupt; W.P. Cofino; K. Lammertsma

• Publisher: Elsevier Science
• Year: 1983
• Tongue: French
• Weight: 218 KB
• Volume: 24
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)81781-5

✦ Synopsis

The 'H NMR spectra of [S]metacyclophane C&t, and of its 8,11-dichloro derivative & are reported. 2 Has a rigid conformation A between -50 and +150°C. Conformation A is also the preferred one (85%) for l& at -47 OC, but l&,-A is in equilibrium with a second conformer l&-B, for which spectral parameters can be derived. A and B correspond with two energy minima predicted by MNDO calculations. One of the most intriguing aspects of the recently synthesized small [n]para-' and [n]metacyclophanes' is their stereochemistry, in particular the question of bending of the benzene ring and the conformation of the oligomethylene bridge. Molecular mechanics3 and MNDO 4 calculations have been reported, but X-ray crystal structures are known only for [n]paracyclophanes'. However, NMR spectroscopy has proven to be useful in the elucidation of their conformations. At low tem-