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Dedicated to Professor R. Criegee on the occasion of' his 65th birthdayThe essential structural element of bullvalene is the homotropilidene system. Thus in any discussion of the chemistry of' bullvalene, all bridged homotropilidenes must also be considered. The present article deals with new syntheses and with the thermal behavior of the homotropilidene system and of bullvalene. Emphasis is also placed on the syntheses and the NMR-spectroscopic behavior of complexed bullvalene, of monosubstituted, disubstituted, and fused bullvalenes, and of some benzobullvalene derivatives.

1415radical anion (1110) has been noticed by previous workers [6]. This unsatisfactory feature seems thus to be shared not only by the radical anion of the 6-phenylderivative ( I F ) , but also by that of the structurally related azuleno[5.6.7-cd]phenalene (Ie).It is tempting to use the HMO model of I for an estimation of the energy gap between the orbitals ys and y~. The diagram of Figure 6 suggests a value less than 0.1 [ B I m 0.25 eV if the number R is not decreased below 0.75. Such a small energy gap might result in a triplet ground state of the dianion la@. However, although this dianion is readily formed, its glassy solution in MTHF fails to display ESR. signals characteristic of the triplet state (cj. Experimental Part). It must therefore be coneluded that 12e has a singlet ground state and that more sophisticated MO methods itre required to rationalize this finding in terms of orbital energies. Support by the Schweizerischer Nationalfonds zur Forderung der wissenschaftlichen Forschung(h-oject Nr. 2.824.73) is acknowledged.Summary. The potential advantages of 13C-(1H-noise decoupled) spectroscopy (in the Fourier transform mode) over 1H-spectroscopy for the quantitative investigation of molecular dynamic processes is discussed. The Co$e rearrangement in bullvalene, an example of complex exchange of spins over different magnetic sites, has been studied by both kinds of spectroscopy as a test.