After a general description of the configuration, of the conformation and of the fast and reversible dynamic processes characteristic of the annulenes, results ofan experimental study of [8], [12], [14], [16] and [18]annulenes by N.M . . R. spectroscopy are presented. Theoretical analysis of the N.M.R. line shape has allowed a determinati9n of the structures of these compounds and of the thermodynamic and kinetic parameters of their dynamic processes. Study of bond shift in cyclooctatetraene (COT) and of bond shift and ring inversion in alkoxy-COT's point to a small negative resonance energy in the planar conformation of COT. Two configurations of [16Jannulene in 3:1 ratio, coded 85 and 91, have been found in solution. Both of them undergo isodynamical conformational mobility and bond shift and a fast exchange between both is also occurring. The newly synthesized [12]annulene of configuration 21 undergoes extremely fast conformational mobility but no bond shift. Conformational mobility is rather slow in [18]

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SummaryThe UV./VIS. absorption spectrum of [ 18lannulene has been remeasured in 3-methylpentane at room and at liquid nitrogen (glass) temperature and interpreted by the CNDO/S-CI-method. The confrontation of the experimental electronic transitions with the CNDO/S-CI-calculated ones favors a structure with D6h-symmetry, i.e. a structure with delocalized z-bonds.

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(1 9.W 1.85)Using the 'permutation of indices' method proposed by Kupian and Fruenkel, we could formulate the density-matrix equations required to lit the temperature-dependent I3C-NMR spectra observed with the title compounds. For 6Li'3CHBr2 (1) and 6Li'3CH2SC,H, (2) an exchange mechanism is proposed by which monomers interchange C-and Li-atoms via a non-observed dimeric intermediate; the activation parameters of these intermolecular dynamic processes have been found to be A H # = 10.2 kcal/mol, AS' = 13.7 cal/mol.K for 1 and A H # = 11.1 kcal/mol, A S # = 20.6 cal/mol.K for 2 ((D,)THF as solvent). In the case of ('Li)butyllithium (3), the observed low-temperature spectra indicate that dimeric (3b) and tetrameric (3a) species are in dynamic equilibrium interchanging the C3H,"CH2 groups (and THF molecules) bonded to the 6Li-atonis. The relative concentrations of the dimer and of the tetramer have been determined by peak integration or by line-shape fitting; the 'pseudo'-equilibrium constant, defined by KLq = [3bI2/[3a], was found to be 2.6 -mol/l (at -88") and corresponds to dG, (-88") = 2 AGi(3b) -dGi(3a) = 1.34 kcdl/mol. The activation parameters of the dynamic process responsible for the exchange were estimated as A H # = 3.78 kcal/mol and A S z = -31.3 cal/mol.K. Tentative interpretation of thc thermodynamic and kinetic parameters is given.

Following the observation that allyl radicals trapped in an argon matrix can be photolytically converted into cyclopropyl radicals (λ = 410 nm, 18 K), the IR spectrum of the cyclopropyl radical was recorded for the first time and interpreted. Bicyclopropane and cyclopropane are formed when the photolysed argon matrix is warmed from 18 to 35 K. The identification of these new species unequivocally proves the presence of cyclopropyl radicals in the photolysed matrix. This radical is shown to be a σ‐type (Cs symmetry) and not a π‐type (C2v symmetry) radical; of the 18 normal frequencies of the Cs cyclopropyl radical, all active in the IR, 16 were observed and were assigned to their corresponding normal modes. For this assignment advantage was taken of ab initio frequency computations reported in the literature and performed by the authors.

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.