Cyclic voltammetry is used to derive HOMO energies of the 1phenyl-2-pyrazolines containing electron-donating or electron-withdrawing substituted phenyl rings and or naphthalenyl substitution on the C 3 -or C 5positions 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 C 3 -aryl ring has significant effect via its π-donor/acceptor ability, compared to the σ-donor/ acceptor ability of the C 5 -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 methoxysubstituted 2-pyrazolines, the HOMO → LUMO is the most intense transition. While the strong acceptor NO 2 substitution on all positions of either C 3 -or C 5 -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).
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