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Cyclic Voltammetric Study of 3,5-Diaryl-1-phenyl-2-pyrazolines

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journal contribution
posted on 05.03.2019, 00:00 by Marzieh Soltani, Reza Minakar, Hamid R. Memarian, Hassan Sabzyan
Cyclic voltammetry is used to derive HOMO energies of the 1-phenyl-2-pyrazolines containing electron-donating or electron-withdrawing substituted phenyl rings and or naphthalenyl substitution on the C3- or C5-positions of the heterocyclic ring to investigate the steric and electronic effects of the aryl substitutions and the type of aryl system on their electrochemical behaviors. The optical HOMO–LUMO gaps needed for the calculation of LUMO (excited state) energies of these compounds are obtained from their UV–vis spectra. Results show that the substitution on the C3-aryl ring has significant effect via its π-donor/acceptor ability, compared to the σ-donor/acceptor ability of the C5-aryl ring, on the CV oxidation peak and onset potentials. Comparative analysis showed very good agreement between the experimentally obtained HOMO and (apparent) LUMO energies and the (TD)­DFT/6-311++G­(d,p) calculated ground and excited states energies. These computational results indicate also that for all chloro- and methoxy-substituted 2-pyrazolines, the HOMO → LUMO is the most intense transition. While the strong acceptor NO2 substitution on all positions of either C3- or C5-aryl rings, except for one compound, increases the intensity of the HOMO → LUMO+1 (LUMO+2) transition significantly, the first (the first two) transition(s) HOMO → LUMO (and HOMO → LUMO+1) has (have) much smaller or negligible intensity (intensities).