Primary Dissociation Pathway Research Articles

Influence of substituents on cation–π interactions: 5. Absolute binding energies of alkali metal cation–anisole complexes determined by threshold collision-induced dissociation and theoretical studies

Threshold collision-induced dissociation (CID) techniques are employed to determine the bond dissociation energies of cation–π complexes of anisole and the alkali metal cations. Both mono and sandwich complexes to Li +, Na +, K +, Rb +, and Cs + are examined. In every complex, the primary and lowest energy dissociation pathway observed is endothermic loss of an intact anisole ligand. Sequential dissociation of a second anisole ligand is observed at elevated energies in the sandwich complexes. Ligand exchange reactions to produce M +Xe and M +(C 6H 5OCH 3)Xe are also observed as minor reaction pathways. The molecular constants necessary for the thermodynamic analysis of the experimental data as well as the structures of these complexes are determined from B3LYP/6-31G ∗ calculations. Theoretical binding energies are determined from single point calculations at the MP2(full)/6-311+G(2d, 2p) level using the B3LYP/6-31G ∗ optimized geometries. The agreement between theory and experiment is very good in all cases except for the Li +(C 6H 5OCH 3) complex. The trends in the bond dissociation energies of these complexes to anisole as well as those to other π ligands previously studied, aniline, benzene, fluorobenzene, phenol, and toluene, confirm that these cation–π complexes are noncovalently bound. Comparisons amongst these π ligands are made to examine the influence of the substituent on the binding, and the factors that control the strength of cation–π interactions.

Photodissociation and photoisomerization pathways of the HNCN free radical

The photodissociation spectroscopy and dynamics of the HNCN free radical have been investigated by fast beam photofragment translational spectroscopy. Predissociative transitions for both the B̃ 2A′←X̃ 2A″ band and a higher-energy band system assigned to the C̃ 2A″←X̃ 2A″ band were observed. Photofragment mass distributions indicate that N2 loss is the primary dissociation pathway. Translational energy distributions reveal a resolved vibrational structure of the N2 fragment, suggesting that the HNCN radical first isomerizes to a cyclic HCN2 intermediate. A dissociation mechanism is proposed in which electronically excited HNCN undergoes internal conversion to the ground state, followed by isomerization to cyclic HCN2 and dissociation through a tight three-center transition state. The HNCN bond dissociation energy D0 and heat of formation ΔfH0(HNCN) were determined to be 2.80±0.03 eV and 3.35±0.03 eV, respectively.

Dissociation dynamics of CF 3C(O)X compounds (where X = H, F and Cl)

Dissociation pathways of CF 3C(O)H, CF 3C(O)F, and CF 3C(O)Cl are studied using ab initio molecular orbital theory. Equilibrium geometries and transition state structures are fully optimized. Heats of reaction and activation energies are computed by using the Møller-Plesset perturbation theory with and without annihilation of spin contamination for molecular and free radical dissociation pathways. A new primary dissociation pathway is predicted to be the most favorable reaction route to dissociation for CF 3C(O)H, CF 3C(O)F and CF 3C(O)Cl. It is the 1,2-CF 2 molecular elimination process that forms CF 2 radicals and HFCO, F 2CO or FClCO. In the case of CF 3C(O)Cl, the extrusion of chlorine atoms to yield CF 3CO radicals is the next pathway which could compete with the 1,2-CF 2 elimination route.

Matrix isolation evidence for a primary co dissociation pathway in the photochemistry of the metal-metal bonded dimers (η 5-C 5H 5) 2M 2(CO) 6 (M = Mo, W)

Photolysis of the metal-metal bonded dimers (η 5-C 5H 5) 2M 2(CO) 6 (M = Mo, w) in polyvinyl chloride film (12–77 K) and frozen gas (12 K) matrices leads to the formation of the novel dimers (η 5-C 5H 5) 2M 2(CO) 5 which have a structure suggested, on the basis of IR spectroscopy, to contain a four electron donor bridging CO ligand and two semi-bridging CO ligands.