Fluxional molecules bullvalene

The notion of a fluxional structure is introduced through the (CH)io molecule bullvalene. In this molecule, a given... 

Bullvalene is a fluxional molecule that undergoes a series of [3,3] sigmatropic shifts which make all 10 carbons in the molecule equivalent. Use arrows to show at least one of the [3,3] sigmatropic shifts. Can you explain the observation that at 120° the proton NMR spectrum of this molecule shows only one peak at 4.2 ppm [41,42]... 

In his efforts to lower the activation energy for the Cope rearrangement, Doerlng designed the first fluxional molecule homotropUldine (79). Barbaralane (80), bullvalene (81), and semibullvalene (68) are each related to 79 as homotropilidines locked in the appropriate Cope conformation (79b). As a conse-... 

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... 

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... 

Schroder was alert enough to understand what had happened, and went on to a highly successful career that included an examination of the properties of bullvalene and substituted versions of this molecule. Doering s predictions were completely confirmed by Schroder s synthesis. Other neutral, completely fluxional organic molecules have not appeared, although the phenomenon of fluxionality appears to be rather more common in organic cations and organometallic compounds. 

Bullvalene (Section 20.7) Bullvalene is the only known neutral organic molecule with a fluxional structure. Every carbon of this (CH)io compound is bonded on time average to each of the other nine carbons. 

---