Bullvalene molecule

Rapid interconversion of the nuclei takes place in the bullvalene molecule under very mild conditions in fluid media. This process involves making and breaking bonds, but this is accompanied by only very small shifts in the nuclear positions. The molecular formula is (CH)io and the carbon skeleton is shown at the top of Figure 3-49. There are only four different kinds of carbon positions (and hydrogen... 

The only complex having olefinic double bonds alone in the coordination sphere of the silver ion which has been subjected to a complete structural analyses (404) is the bullvalene (532) complex (CioHjo)sAgBF4. The structure consists of discrete (CioHio)3Ag+ cations and BF4 anions (Fig. 12). The three bullvalene molecules in the complex cation are... 

A rapid interconversion of the nuclei takes place in the bullvalene molecule under very mild conditions in fluid media. This process involves... 

The presence of symmetry is also an important factor in linear syntheses provided that an element of symmetry is maintained during the course of a synthetic sequence. For instance, one of the syntheses of bullvalene (12) -a molecule that possesses a C3 axis of symmetry- starts from chloroform, and proceeds then through methane(triacetic) acid (9), the corresponding tris-a-diazoketone (10) and bullvalanetrione (11). molecules which all have a C3 axis of symmetry (Scheme 4.3) [16]. 

The most intriguing hydrocarbon of this molecular formula is named bullvalene, which is found in the mixture of products of the reaction given above. G. Schroder (1963, 1964, 1967) synthesized it by a thermal dimerization presumably via diradicals of cyclooctatetraene and the photolytical cleavage of a benzene molecule from this dimer. The carbon-carbon bonds of bullvalene fluctuate extremely fast by thermal Cope rearrangements. 101/3 = 1,209,600 different combinations of the carbon atoms are possible. 

The most prominent example of a totally degenerate neutral molecule is bullvalene [1], a CioHio molecule in which all CH-groups exchange with each other through a series of Cope rearrangements (Doering and Roth, 1963). At + 100°C these rearrangements are so fast that in the H-nmr spectrum of... 

However, some substrates, generally rigid bicyclic molecules, (e.g., barrelene, p. 152, which is converted to semi-bullvalene) give the di-7i-methane rearrangement only from triplet states. 

The successful quest for bullvalene led to the investigation of a number of similar molecules. The fluxional behaviour of dihydrobullvalene (295) was apparent from its H-NMR spectrum at room temperature . This showed two type A protons which remain vinylic after Cope rearrangement, d 5.63 for type B S 3.68. The type C protons absorb at ca. d 1.87 and overlap with the methylene protons. The observed coupling... 

An intriguing new fused thiophene derivative, trithia-[3]-peristylane 53, has been prepared from bullvalene 54, which underwent initial ozonolysis, followed by acetalization, to provide the intermediate 55. This material was subsequently subjected to Lawesson s reagent (LR) to give the target molecule 53. A detailed structural study of this Csv symmetric structure was also conducted <04OL1617>. 

X 10 s at 25° At 10° C, the H-NMR spectrum of bullvalene exhibits a single peak at 4.22 ppm, which indicates the fluxional nature of the molecule. Owing to the threefold axis of symmetry present in bullvalene, the degenerate rearrangement results in all of the carbons having an identical averaged environment. This is illustrated in the... 

At low temperatures (below -85°C), the proton NMR spectrum of bullvalene consists of four complex multiplets (none of the protons is equivalent to any other proton in the molecule). As the temperature is raised, however, the multiplets broaden and move closer together. Eventually, at -l-120°C, the entire spectrum consists of one sharp singlet. 

The central molecules from this saga of the 1960s are the potentially aromatic cyclodecapentaenes and bullvalene, a compound of 10/3 faces. Efforts directed to the synthesis of these compounds involved thermal, photochemical, and metal-catalyzed processes which not only accomplished the major task but also generated... 

Many examples of tbis4j e oCrearrangement are known, one of the more interesting being that o ullvalene, ch is converted into itself with a first-order rate constant of 3440 sec dl 25"C." At 100 C, the NMR spectrum of bullvalene exhibits only one peak at 5.78 r, indicative of the fluctional nature of the molecule. The free energy of activation for the rearrangement has been determined as 12.8 kcal/mol, a very low value indeed. ... 

Koritsanszky T, Buschmann J, Luger P (1996) Topological analysis of experimental electron densities the different C—C bonds in bullvalene. J Phys Chem 100 10547-10553 Stolevik R, Postmyr L (1997) Bond length variations in molecules containing triple bonds and halogen substituents. J Mol Struct 403 207-211... 

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