Multifaceted consequences of holding two [8]annulene rings face-to-face. Synthesis, structural characteristics, and reduction behavior of [22](1,5)cyclooctatetraenophane

Abstract

The doubly-decked [8]annulene 11 has been prepared in 13 steps from the known diketone 15. The scheme takes advantage of the aramia ting capacity of the Cook-Weiss reaction and the ability of semibullvalenes to undergo thermal isomerization to cyclooctatetraenes. The bis(semibullvalene) 12 is both conformationally dynamic and subject to very rapid Cope rearrangement.The energetics of inversion within its interconnective cyclooctane ring have been elucidated by variable-temperature NMR spectroscopy. The structural nature of 11 has been made clear by a combination of molecular mechanics calculations and

Cyclooctatetraenophanes: A Computational Study

“…MP2 is a bit of an outlier, predicting a shorter inter-ring separation. These results suggest that these computational methods are 4 All of the computations are consistent with this observation; 2a is 6−10 kcal mol −1 below 2b. The energy difference at the ωB97XD, B3LYP-D3, and M06-2x levels are clustered around 8 kcal mol −1 .…”

“…3 Their main interest was to examine the possibility of bond-shifting, which interconverts conformers 2a and 2b. The X-ray structure analysis revealed just conformer 2a, 4 consistent with molecular mechanics computations that indicated that 2a is 3 kcal mol −1 lower in energy than 2b.…”

“…This is a larger energy separation than that predicted by the MM computations, but is consistent with the observation of only a single isomer, 2a, in the X-ray crystal structure. 4 The two functionals that account for dispersion (ωB97X-D and B3LYP-D3) give structures very similar to the X-ray structure of 2a; this can be best identified with the distance between the ring centers (r sep ) listed in Table 2. The M06-2x and MP2 structures are slightly contracted, and as expected, B3LYP predicts a structure with the rings too far apart.…”

“…These conformers are of D 2 and C 2 symmetry, as are the two isomers identified in Paquette's MM study. 4 For all computational levels, 2a is found to be lower in energy than 2b, by 6−10 kcal mol −1 (see Table 2). This is a larger energy separation than that predicted by the MM computations, but is consistent with the observation of only a single isomer, 2a, in the X-ray crystal structure.…”

Erweiterung und Revision des von-Baeyer-Systems zur Benennung polycyclischer Verbindungen (einschlie��lich bicyclischer Verbindungen)

“…Anmerkung : Unter gewissen Umständen (siehe beispielsweise Lit. 15) wurden in einem anscheinend vollständig konjugierten Ring lokalisierte Doppelbindungen festgestellt. Die genaue Lage der Doppelbindungen kann durch das vorangestellte Symbol Δ mit dem hochgestellten Lokanten (oder zusammengesetzten Lokanten) für die am niedrigsten nummerierte betreffende Doppelbindung angegeben werden (siehe FR‐9.2,12 Fußnote zu B‐1.26).…”