Quantum chemical insight into the reactivity of 1,3-dipoles on coronene as model for nanographenes

Resumo

In this paper, we present a systematic investigation into reactivity of 1,3-dipoles on coronene as model for nanographenes using the density functional theory (DFT). The calculations show that the dipole nature mainly involving the structure and electrical effect is the major influence on reactivity. The 18-valence-electron azomethine ylides shows more active than the other two types of 1,3-dipoles with 16-valence-electron to NG, which may due to a smaller singlet-triple splitting. The more electronegative terminate group leads a higher stability and chemical inertness of the 1,3-dipole. There the reactivity order is oxide < imine < ylide. The varied distortion energy which determines the activation energy depends on the deformation of the 1,3-dipole. It can be obviously observed the distortion energy increases as the strengths of two resonance bonds of the 1,3-dipole increase in each series. The less electronegative terminate group leads the more electron-deficient and the less electron delocalization of the 1,3-dipole and even the more stable of the intermediate, which leads the cycloaddition proceed easier. The trend that the activation energy decreases as the strengths differences of the two new bonds of intermediate is also very clear in each series. All the reactivities are consistent analyzing in frontier molecular orbitals (FMO) theory. Unlike the 1,3-DC toward some other dipolarophiles, the vast majority of the studied 1,3-dipole cycloaddtions (DC) are of largely negative Gibbs free energies (ΔG^≠) values which are spontaneous at the temperature. There is correlation between the extent of spontaneous of reaction and the activation energy. There is also good relationship between the activation energy and the reaction energy, which follows the Hammond postulate.