C4H4 radical cation isomers: Generation, structure, stability, and isomerization reactions

Publication date: 1 September 2017 Source:Computational and Theoretical Chemistry, Volume 1115 Author(s): Kiew Shaphrang Kharnaior, Asit K. Chandra, R.H. Duncan Lyngdoh The B3LYP, M06-2X and MP2 methods are used to study the generation, relative stability, structure, charge and spin distributions, along with isomerization reactions, of C 4 H 4 + radical cations in gas phase. The highly endothermic generation of C 4 H 4 + species by ionization of neutral C4H4 precursors is for 7 cases. Stability orders for 10 C 4 H 4 + isomers as derived from the three methods correlate well with one another, where methylenecyclopropene radical cation is the global minimum. Available computational data also agrees well with these orders, and experimental data fairly well. The charge and spin distributions describe one isomer as distonic (with charge and spin separated). Concerted isomerization reactions for the methylenecyclopropene, butatriene, vinylacetylene and methyleneallene radical cations and 2 hypothetical higher energy species proceed via well-defined transition states described with regard to their relative positions along the reaction coordinate in accordance with Hammond’s postulate. These one-step isomerizations are combined to yield five multi-step conversions of various C 4 H 4 + species to the lowest energy methylenecyclopropene isomer. The application of transition state theory and computation of rate coefficients leads to the est...

Source: Computational and Theoretical Chemistry - June 26, 2017 Category: Chemistry Source Type: research