No abstract

The gas-phase reactivity of La2+ with Q-Q linear alkanes is investigated and compared to the analogous reactions of La+. La2+ is unreactive with methane and ethane but reacts with propane and butane to give dehydrogenation, alkane loss, and for butane charge-splitting reaction products. Interestingly, charge transfer is not observed in agreement with a simple curve-crossing model. Four ligated species, namely, LaC2H4+, LaC2H42+, LaC3H6+, and LaC3H62+, are photodissociated and the photodissociation thresholds are used directly, or together with information from ligand displacement reactions, to assign thermochemical values for these processes and metal ligand bond energies. The bonding properties of LaC2H2+ and LaC2H22+ are also investigated. A surprising outcome of this study is that the monocation is in some cases more strongly bound to these ligands than the dication. Theoretical calculations by Bauschlicher and co-workers are in good agreement with these results.

The reactions of phenylium with water and ammonia and their methyl homologs have been investigated using a quadrupole ion trap and semiempirical molecular orbital calculations. The results indicate that both types of molecules react with phenylium through lone pair electrons even though, for methyl-containing compounds, insertion into a C-H bond would lead to more stable products. For the excited adducts formed by reaction with methyl-containing reactant neutrals, the only dissociation observed is loss of a methyl radical. Neutral losses of H2 or CH4, which are more thermodynamically stable, are not observed, which indicates that these reactions are either not kinetically competitive or have high energy transition states due to the fact that the reactions would need to occur via orbital symmetry forbidden 1,2 eliminations.

The gaseous near-infrared and visible absorption spectra of pyrrole and pyrrolidine have been measured for the first through fourth N-H stretch vibrational overtones and the second through fourth C-H stretch overtones. The C-H overtone features follow the simple local mode expression with anharmonicities of 53.9 f 0.5 cm-' for pyrrole and 60 f 2 cm-' for pyrrolidine. Multiple transitions observed in the N-H stretching regions indicate the presence of vibrational coupling to other vibrational modes. This assignment is confirmed by the first and third N-H vibrational overtone spectrum of gaseous pyrrole-d4. For comparison, the visible spectra of neat liquid pyrrole, dilutions of pyrrole in carbon tetrachloride, and neat liquid pyrrolidine were obtained by direct absorption spectroscopy. The pattern of multiple peaks for the N-H absorption region also appears (shifted 200 cm-l to the red) in solution-phase pyrrole. This shift of all the peaks results from the intermolecular interactions of the N-H in the liquid; however, the preservation of the peak splittings indicates that this splitting is a result of intramolecular vibrational coupling. The spectrum of pyrrolidine is remarkably similar to that of pyrrole, suggesting the same vibrational coupling exists for both compounds.

No abstract