Molecular Rods. 1. Simple Axial Rods.

Bicyclo[1.1.1]pentanes, [n]Staffanes, [1.1.1]Propellanes, and Tricyclo[2.1.0.02,5]pentanes

Resonance Energy Calculation; the MM2ERW Force Field*



The additivity of the thermochemical conjugation energy in acyclic systems allows one to extend force-field calculations to conjugated π systems without embarking on quantum-mechanical methods. The approach fails with cyclic delocalized systems, where resonance effects become important. Here the method provides the reference value needed to calculate resonance energies.

Die Berechnung von Resonanzenergien; das MM2ERW‐Kraftfeld

Propellanes are a unique class of compounds currently consisting of well over 10 000 representatives, all featuring two more or less inverted tetrahedral carbon atoms that are common to three bridging rings. The central single bond between the two bridgeheads is significantly weakened in the smaller entities, which leads to unusual reactivities of these structurally interesting propeller-like molecules. This Review highlights the synthesis of such propellanes and their occurrence in material sciences, natural products, and medicinal chemistry. The conversion of [1.1.1]propellane into bridgehead derivatives of bicyclo[1.1.1]pentane, including oligomers and polymers with bicyclo[1.1.1]penta-1,3-diyl repeat units, is also featured. A selection of natural products with larger propellane subunits are discussed in detail. Heteropropellanes and inorganic propellanes are also addressed. The historical background is touched in brief to show the pioneering work of David Ginsburg, Gunther Snatzke, Kenneth B. Wiberg, Gunter Szeimies, and others.

Propellanes-From a Chemical Curiosity to "Explosive" Materials and Natural Products.

Kyle F. Biegasiewicz,† Justin R. Griffiths,‡ G. Paul Savage, John Tsanaktsidis, and Ronny Priefer* †Department of Chemistry, University of Rochester, Rochester, New York 14627-0216, United States ‡Department of Chemistry, University at Buffalo, Buffalo, New York 14260-1660, United States Ian Wark Laboratory, CSIRO Manufacturing Flagship, Bayview Avenue, Clayton, Victoria 3168, Australia College of Pharmacy, Western New England University, Springfield, Massachusetts 01119, United States

Cubane: 50 years later.

Die Kinetik der entarteten Cope-Umlagerungen der Titelverbindungen wurden mittels dynamischer 13C-NMR-Spectroskopie gemessen. Die aus den NMR-Linienformanderungen abgeleiteten Reaktionsgeschwindigkeitskonstanten k lieferten auf der Basis der Eyring-Gleichung folgende Aktivierungsparameter: Semibullvalen (1) ΔH≠ = 5.2 kcal mol−1, ΔS≠ = –3.2 cal K−1 mol−1, ΔG≠298 = 6.2 kcal mol−1; 1,5-Dimethylsemibullvalen (2) ΔH≠ = 4.5 kcal mol−1, ΔS≠ = –1.6 cal K−1 mol−1, ΔG≠298 = 5.0 kcal mol−1; 2,6-Dibrom-1,5-dimethylsemibullvalen (3) ΔH≠ = 7.5 kcal mol−1, ΔS≠ ≈ 0 cal K−1 mol−1, ΔG≠298 = 7.4 kcal mol−1. Die Substituenteneffekte werden mit denen anderer substituierter Semibullvalene verglichen und im Hinblick auf die Natur des Ubergangszustandes der Cope-Umlagerung in uberbruckten Homotropilidenen diskutiert. Die fur 2 bestimmte Barriere ist die niedrigste, die bisher mit der dynamischen NMR-Spektroskopie gemessen wurden.



Applications of 13C-NMR Spectroscopy, XXVII. – Activation Parameters off the Cope Rearrangements of semibullvalene, 1,5-Dimethylsemibullvalene, and 2,6-Dibromo-1,5dimethylsemibullvalene



The kinetics of the degenerate Cope rearrangements of the title compounds were measured by dynamic 13C-NMR spectroscopy. The rate constants derived from the changes in NMR lineshape yielded, on the basis of the Eyring equation, the following activation parameters: semibullvalene (1) ΔH≠ = 5.2 kcal mol−1, ΔS≠ = –3.2 cal K−1 mol−1, ΔG≠298 = 6.2 kcal mol−1; 1,5-dimethylsemibullvalene (2) ΔH≠ = 4.5 kcal mol−1, ΔS≠ = –1.6 cal K−1 mol−1, ΔG≠298 = 5.0 kcal mol−1; 2,6-dibromo-1,5-dimethylsemibullvalene (3) ΔH≠ = 7.5 kcal mol−1, ΔS≠ ≈ 0 cal K−1 mol−1, ΔG≠298 = 7.4 kcal mol−1. The substituent effects are compared with those of other substituted semibullvalenes and are discussed with respect to the nature of the transition state for the Cope rearrangement of bridged homotropilidenes. The barrier for 2 is the lowest measured so far by dynamic NMR spectroscopy.

Anwendungen der 13C‐NMR‐Spektroskopie, XXVII. Die Aktivierungsparameter der Cope‐Umlagerung von Semibullvalen, 1,5‐Dimethylsemibullvalen und 2,6‐Dibrom‐1,5‐dimethylsemibullvalen

A body-diagonal bond in cubane: can it be introduced?

Photochemically induced addition of [1.1.1] propellane across one or both of the C-I bonds in the 1,4-diiodocubane and 1,4-diiodobicyclo [2.2.2] octane yields doubly terminally functionalized straight molecules («mixed staffanes») whose length is intermediate between those of the parent [n] staffanes differing by one in the value of n. Conversion to terminal dilithio derivatives and to the parent hydrocarbons is described, and a single-crystal X-ray structure of 1,4-bis(bicyclo [1.1.1] pent-1-yl) cubane is presented

"Mixed staffanes" as intermediate-length staffs for molecular-size tinkertoys. Parent hydrocarbons and terminal diiodides combining bicyclo[1.1.1]pentane with cubane or bicyclo[2.2.2]octane units

Synthese d'oligomere [n] staffanes (n=1 a 6) a partir de [1,1,1] propellane et d'argon ou d'hydrogene ou d'ammoniac

[n]Staffanes: the parent hydrocarbons

Transannular (orbital) interactions in compounds 1–9 are studied by means of He(Iα)-PE spectroscopy. Unusually strong through-space-dominated π,π interaction is found to be operative in the nonconjugated 1,6-dienes 1, 2, 7, and 8. The π,π splitting of 1.9 eV for disecododecahedradiene 1 is even surpassed by the record value of 2.2 eV for disecodienedione 2, which almost equals that in 1,3-butadiene (2.46 eV). The experimental results are explained by computational methods, especially by analyses of the precanonical MOs.

Small and Medium Rings, 771) Nonconjugated π,π Interactions Approaching Classical π,π Conjugation – PE‐Spectroscopical Investigation of the 7,8;12,19‐Diseco‐1,16‐dodecahedradiene System

Karin Hassenrück

Papers

Anwendungen der 13C‐NMR‐Spektroskopie, XXVII. Die Aktivierungsparameter der Cope‐Umlagerung von Semibullvalen, 1,5‐Dimethylsemibullvalen und 2,6‐Dibrom‐1,5‐dimethylsemibullvalen

A body-diagonal bond in cubane: can it be introduced?

"Mixed staffanes" as intermediate-length staffs for molecular-size tinkertoys. Parent hydrocarbons and terminal diiodides combining bicyclo[1.1.1]pentane with cubane or bicyclo[2.2.2]octane units

[n]Staffanes: the parent hydrocarbons

Small and Medium Rings, 771) Nonconjugated π,π Interactions Approaching Classical π,π Conjugation – PE‐Spectroscopical Investigation of the 7,8;12,19‐Diseco‐1,16‐dodecahedradiene System