[en] Ion-molecule reactions of C₃H⁺₄ with C₃H₄ in cyclopropene/propyne and allene/propyne mixtures as well as in pure cyclopropene and allene are studied by a photoionization mass spectrometer. Product distributions of C₃H⁺₃, C₆H⁺₅, and C₆H⁺₇ differ in intensity from one system to another. Such differences are attributed to the nature of reactants and intermediates. The structure of the neutral molecule is especially significant in determining the product distribution. (orig.)

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[en] Comprehensive ab initio (MCSCF) and (CI) calculations are performed to determine properties of the cyclopropenyl radical, which has not yet been directly observed experimentally. Jahn-Teller distortion is responsible for a dramatic change from the high-symmetry D/sub 3h/ π radical parent structure to a low-symmetry nonplanar C/sub s/ sigma radical equilibrium structure. The equilibrium structure is found to be an ethylenic form that can exist in three equivalent conformations. These can interconvert (via a pseudorotation of the carbon-carbon double bond around the ring) by passing through a nonplanar allylic transition state. Planar geometries turn out to be of such high energy as to play no significant role in the dynamics of this system. Large-scale CI calculations, with corrections for differences in zero-point vibrational energies, indicate the pseudorotation barrier height to be about 3-4 kcal/mol. Qualitative results are obtained for the energy and geometry changes that occur along the interconversion path. A number of one-electron properties are also reported for the equilibrium form. Notable among these are the spin-density predictions, which should be of use in experimental identification of the cyclopropenyl radical by ESR spectroscopy. A qualitative survey of the energies and geometries of other C₃H₃ isomers is also presented

[en] In order to study the diastereotopically secondary deuterium isotope effects on the thermal isomerization of cyclobutane, the compounds cyclobutene, [1-²H]cyclobutene, and [3-²H]cyclobutene were prepared, and their gas-phases isomerizations were followed. From the data, correlations between hybridization changes and secondary hydrogen/deuterium isotope effects and the observed diastereotopically distinct hydrogen/deuterium effects suggest that two cyclobutene C3-H bonds may have substantially different hybridizations at the transition state. 16 refs

[en] Application of the McMurry reaction in the synthesis of thermally stable photochromic dihetarylethenes is described. Hetaryl rings in the target molecules are connected to the double bond of the cycloalkenes or heterocycles formed upon the McMurry cyclization.

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[en] In our previous publications it has been shown that the method of Benson's group permits the estimation of the enthalpies of vaporization of organic compounds. In the present paper we have applied this method for unsaturated hydrocarbons, thus completing our previous work on acyclic alkenes. For the alkylbenzenes we have changed the values of the groups C-(Csub(b))(C)(H)₂ and C-(Csub(b))(C)₂(H) previously determined. A more accurate value for the enthalpies of vaporization of the alkylbenzenes of higher molecular weight is obtained. (orig.)

[en] The soft-phonon instability of the metallic state is investigated in the case of systems where there are several partially filled bands. It is shown that the instability is the consequence of a certain symmetry between the electrons and holes in the vicinity of the Fermi surface. The transition is stable with respect to small perturbations of the band structure. An estimate is made for the transition temperature of TTF-TCNQ. (author)