title: Three isomeric bis(methoxycarbonyl)[2.2]paracyclophanes.
abstract: The title isomers 4,16- (pseudo-ortho), 4,15- (pseudo-gem) and 4,12-bis(methoxycarbonyl)[2.2]paracyclophane (pseudo-para), C(20)H(20)O(4), all show the typical structural features of [2.2]paracyclophanes (flattened boat conformation of the rings, lengthened single bonds in the bridges and narrow ring angles at the bridgehead atoms). The 4,12-isomer displays crystallographic inversion symmetry. The carbonyl groups adopt a conformation in which they are directed away from the ring systems towards the nearest bridge; the corresponding angle at the ring substituent atom is widened. Crystal packing involves C-H.pi interactions for the 4,15-isomer and weak C-H.O hydrogen bonds for the other two isomers.
authors: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Postfach 3329, 38023 Braunschweig, Germany. jones@xray36.anchem.nat.tu-bs.de
authors: Peter G
authors: PG
authors: Jones
authors: Jörg
authors: J
authors: Hillmer
authors: Henning
authors: H
authors: Hopf