Alkyl chain effect (ethyl, propyl and butyl) on the dehydrogenation mechanism of H12-N-alkylcarbazoles has been investigated theoretically under various different conditions. Gibbs energies of activation of about 107.88 kcal.mol-1 have been determined as the least energy barriers among the studied dehydrogenation processes for dehydrogenation of H12-N-ethylcarbazole to H4-N-ethylcarbazole in decalin and 57.44 kcal.mol-1 for dehydrogenation of H12-N-propylcarbazole to H8-N-propylcarbazole under the experimental conditions. Kinetic and thermodynamic studies have shown that the route of H4-N-alkylcarbazoles formation passes through a higher barrier than that of the H8-N-alkylcarbazoles. Natural bond orbital (NBO) analysis showed a decrease in electron transfer between πC-C and σ*C-H at the center of the reaction. The electron density of the C-H bonds of the transition states was evaluated as evidence of hydrogen release via quantum theory of atoms in the molecules (QTAIM) procedure. Based on this analysis, a change in the nature of C-H bonds was confirmed from Covalence to electrostatic interactions during the reaction.

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