Heats of Formation of [2.2]Paracyclophane-1-ene and [2.2]Paracyclophane-1,9-diene − An Experimental Study

• Published in: Journal of the American Chemical Society Vol. 125; no. 49; pp. 15110 - 15113
• Main Authors: de Meijere, Armin, Kozhushkov, Sergei I, Rauch, Karsten, Schill, Heiko, Verevkin, Sergey P, Kümmerlin, Martin, Beckhaus, Hans-Dieter, Rüchardt, Christoph, Yufit, Dmitrii S
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 10.12.2003
• Subjects: Chemical thermodynamics; Chemistry; Elements, mineral and organic compounds; Exact sciences and technology; General and physical chemistry; Thermodynamic properties; Heat of sublimation; Enthalpy; Aromatic compound; Cyclophane; Experimental study; Thermodynamic properties; Heat of formation; Macrocycle
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0374628

The enthalpies of formation [Δ (g)] of tricyclo[8.2.2.24,7]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[8.2.2.24,7]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[8.2.2.24,7]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.