title: Heats of formation of [2.2]paracyclophane-1-ene and [2.2]paracyclophane-1,9-diene - an experimental study.
abstract: The enthalpies of formation [Delta(g)] of tricyclo[8.2.2.2(4,7)]hexadeca-1(13),2,4(16),5,7(15),10(14),11-heptaene (2, 1,2-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1-ene) and tricyclo[8.2.2.2(4,7)]hexadeca-1(13),2,4(16),5,7(15),8,10(14),11-octaene (3, 1,2,9,10-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1,9-diene) have been determined by measuring their heats of combustion in a microcalorimeter and their heats of sublimation by the transpiration method. Values of the strain energies (SE) [SE(2) = 34.7 kcal mol(-)(1), SE(3) = 42.0 kcal mol(-)(1)] have been derived from the gas-phase heats of formation and are compared with those from MM3 and PM3 calculations and with the corresponding value SE(1) = 30.1 kcal mol(-)(1) for the parent tricyclo[8.2.2.2(4,7)]hexadeca-1(13),4(16),5,7(15),10(14),11-hexaene (1, [2.2]paracyclophane). The higher strain energies of 2 and 3 (by 4.6 and 11.9 kcal mol(-)(1)) are in accord with the well-known increased reactivities of their aromatic rings as a consequence of their increased bending. As revealed by an X-ray crystal structure analysis, the bending in the monoene 2 corresponds to that of 1 and 3 at one of two bridging corners.
authors.affiliation: Department of Organic Chemistry, University of Göttingen, Tammannstrasse 2, D-37077 Göttingen, Germany. Armin.deMeijere@chemie.uni-gottingen.de
authors.forename: Armin
authors.initials: A
authors.lastname: de Meijere
authors.forename: Sergei I
authors.initials: SI
authors.lastname: Kozhushkov
authors.forename: Karsten
authors.initials: K
authors.lastname: Rauch
authors.forename: Heiko
authors.initials: H
authors.lastname: Schill
authors.forename: Sergey P
authors.initials: SP
authors.lastname: Verevkin
authors.forename: Martin
authors.initials: M
authors.lastname: Kümmerlin
authors.forename: Hans-Dieter
authors.initials: HD
authors.lastname: Beckhaus
authors.forename: Christoph
authors.initials: C
authors.lastname: Rüchardt
authors.forename: Dmitrii S
authors.initials: DS
authors.lastname: Yufit