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CASSCF and CASPT2/6-31G(d) calculations have been performed on the low-lying electronic states of three, non-Kekule, hydrocarbon diradicals: 2-methylenedihydrophenalene-1,3-diyl (2), trimethylenemethane (3), and 1,8-naphthoquinodimethane (4). The computational results reveal how addition of ferromagnetic coupling groups (1,8-naphtho to 3 and vinylidene to 4) modulates the energy differences between the three lowest electronic states of 2-4. The most dramatic effect is the 30.4 kcal/mol change in the relative energies of the (1)A(1) and (1)B(2) states on addition of a vinylidene bridging group to 4 to form 2. The relative energies of the electronic states of 2-4 are discussed in terms of the topologies of the pair of nonbonding MOs for each state of each diradical, and a strategy for making (1)A(1) the ground state of a nitrogen analogue of 4 is proposed.

6,9-Di(tert-butyl)-1-methyltetrazolo[1,5-a]perimidine (1) has been synthesized from naphthalene in seven steps. The EPR spectra, recorded after irradiation of 1 in a butyronitrile matrix at 77 K (lambda = 351 nm) and in Ar and Xe matrixes at 4.6 K (lambdaor = 345 nm), showed a six-line, high-field signal (Delta m(S) = +/- 1), centered at 3350 G in butyronitrile, along with a half-field signal (Delta m(S) = +/- 2), which is characteristic for triplets. Simulation of the observed EPR spectra gave values for the zero-field splitting parameters of |D/hc|/cm(-1) = 0.0105, |E/hc|/cm(-1) = 0.0014 in butyronitrile and |D/hc|/cm(-1) = 0.0107, |E/hc|/cm(-1) = 0.0016 in Ar. These EPR parameters are consistent with the diradical 5,8-di(tert-butyl)-2-(N-methylimino)perimidine-1,3-diyl ((3)2) as source of the EPR spectra. Linearity of the Curie-Weiss plot and UB3LYP and (14/14)CASPT2 calculations of the singlet-triplet energy difference (DeltaE(ST) approximately 8-10 kcal/mol) indicate that the triplet is the ground state of 2, as predicted for such a nondisjoint diradical.

Monocyclic iminoaziridines and exo-endo diastereomers of spirocyclic iminoaziridines that are derived from norbornane are prepared in batches of up to 10 g to foster applications as building blocks in syntheses. N,N'-Disubstituted alpha-haloamidines, which are readily available in two steps from N-substituted alpha-halocarboxamides, are 1,3-dehydrohalogenated by strong bases such as alkali-metal hydrides or tert-butoxides to afford distillable oils or low-melting solids, which consist of slowly interconverting E-Z diastereomers of the title compounds. The scope and limitations are outlined for this reaction. The configurations E and Z that were assigned on the basis of homoallylic 1H-1H coupling and asymmetric solvent-induced shifts required that, in 13C NMR spectra, the observed gamma-effects of substitutents at the imino nitrogens were deshielding, contrary to the well-known shielding gamma-effects in all other types of C=N compounds. However, an NOE NMR study demonstrated unequivocally that the previous assignments are correct and hence the observed gamma-effects actually deshielding. The ranges of 15N NMR chemical shifts span more than 60 ppm. Neither the beta- nor the gamma-effects of substituents on both types of nitrogen follow a uniform increment pattern.

We predict an inverse quantum isotope effect for molecules that may isomerize in a shallow doublowell potential. Here the corresponding fundamental vibrational transition may excite a delocalized state with energy just above the potential barrier. In this case, increasing molecular masses is predicted to yield increasing fundamental frequencies, in marked contrast to the familiar opposite trend in other molecules. The novel effect is illustrated for simple models representing symmetric semibullvalenes, consistent with experimental values for the relevant masses, bond lengths, and NMR and UV spectra

Isomerisation de l'azo-1,1' adamantane, des azo-1,1' bicyclo [2.2.2] octanes et de l'azo-1,1' norbornane-trans en cis-azoalcanes. A 185 nm elimination de N 2 avec augmentation du rendement quantique, avec maintien de l'isomerisation cis-trans. Mecanismes

Bestrahlung des vornehmlich untersuchten Tetrazolins (Ia) in Butyronitril-Matrix im ′ ESR-Spektrometer liefert nach 30 s ein zentrosymm.