(CH)8 hydrocarbons. Photochemistry of tricyclo[3.3.0.02,6]octa-3,7-diene

The Energetics of Aromatic Hydrocarbons: An Experimental Thermochemical Perspective

“…Cyclooctatetraene, or [8]annulene, is the third member of the [ n ]annulene series. Its enthalpy of formation of 295.9 ± 1.7 kJ/mol refers to the most stable all-( Z ) isomer . A recent high-level ab initio study obtained an enthalpy of formation for the most stable D 2 d structure ( 3 ) of 293.2 kJ/mol, very close to the measured value.…”

Hexafluorobenzene Photochemistry: Wellspring of Fluorocarbon Structures

“…The apparent lability of 70 makes sense by analogy to the parent hydrocarbon 68, in which the double bonds interact with one another so effectively via the Walsh orbitals of the central cyclobutane ring that the compound displays substantial UV absorption even beyond 300 nm (where ) ∼190). 67 The interaction both lowers the LUMO and raises the HOMO, resulting in high reactivity. 68 Dechlorination of the Diels-Alder adduct from dichloride 74 and pyrrole yielded 75, which rearranged at 80 °C to 76.…”

“…Therefore, the problem lay in having both double bonds present in the twisted tricyclic skeleton. The apparent lability of 70 makes sense by analogy to the parent hydrocarbon 68 , in which the double bonds interact with one another so effectively via the Walsh orbitals of the central cyclobutane ring that the compound displays substantial UV absorption even beyond 300 nm (where ε = ∼190) . The interaction both lowers the LUMO and raises the HOMO, resulting in high reactivity …”

The Role of the Intersection Space in the Photochemistry of Tricyclo[3.3.0.02,6]octa-3,7-diene

“…Experimental results indicate that irradiation of TOD at −60 °C leads to the concomitant formation of SBV and COT in an approximate ratio of 2:1 (See Scheme ) . The low-temperature ensures that the isomerization of TOD to SBV is negligible in the time-scale of the complete photochemical reaction (i.e., ∼1 h).…”

“…The low-temperature ensures that the isomerization of TOD to SBV is negligible in the time-scale of the complete photochemical reaction (i.e., ∼1 h). Different mechanisms have been proposed for the photochemical rearrangement of TOD to yield COT and SBV, involving a [2+2] retro-cycloaddition for COT and a concerted suprafacial[1,3]-sigmatropic shift for SBV, or the formation of COT and SBV via a highly vibrationally excited biradical intermediate . Nevertheless, none of the mechanisms have been validated by experimental or theoretical studies.…”