| The microwave spectrum of cis-hex-3-ene-1,5-diyne, along with 2H and 13C enriched samples, has been obtained. The spectra displayed rotational-vibrational interactions, which were accounted for with coupled cluster calculations, leading to an accurate equilibrium (Re) structure. The Re structure obtained was in good agreement with high level computations (CCSD(T)/cc-pVTZ) and was consistent with the microwave structures of similar molecules. cis-Hex-3-ene-1,5-diyne is the parent molecule for the Bergman cyclization. The distance between the ends of the alkyne arms (the c--d distance) is commonly used to predict the ease with which Bergman cyclization to the diradical intermediate will occur. The experimental R e structure provides a c--d distance of 4.32 A, which is considerably longer than the commonly reported c--d distance of 4.12 A. The Re structure obtained also indicates that the alkyne arms deviate from linearity, in the direction opposite to the mode of cyclization.;The equilibrium structures (Re) of ( Z)-pent-2-ene-4-ynenitrile and maleonitrile have been obtained in a similar fashion. 15N and 2H isotopomers of both compounds were synthesized to facilitate the R e structure determination. The Re structures obtained via this method displayed good agreement with each other and with related compounds in the literature. The alkyne and cyano linkages were observed to be bent slightly away from the center. The data obtained will allow radio astronomers to search for these molecules in the interstellar medium.;Triplet pentadiynylidene (HC5H) was observed via FT-IR, ESR and UV--vis spectroscopy under matrix isolation conditions. Triplet HC 5H, generated by the long wavelength photolysis of 1-diazo-2,4-pentadiyne, exhibited a good match with the computed (CCSD/DZP) IR spectrum in both N 2 and Ar matrices. ESR spectra obtained in both Ar and methylcyclohexane confirmed the computed triplet ground state of HC5H, but indicated that the molecule deviated, to a small extent, from the computed Dinfinityh symmetry. The UV--vis spectrum of triplet HC5H, in N2, displayed extensive vibrational progressions. Photochemical conditions were explored to effect the photoconversion of triplet HC5H to other C5H2 isomers, but no conditions were found under which HC5H underwent appreciable photochemistry. |
