UV-Vis, IR spectra and thermal studies of charge transfer complexes formed in the reaction of 4-benzylpiperidine with σ- and π-electron acceptors

The reactions of the electron donor 4-benzylpiperidine (4BP) with the sigma-acceptor iodine and pi-acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge-transfer (CT) complexes were recorded. Based on the obtained data, the charge-transfer complexes were formulated as [(4BP)I](+) I-3(-) [(4BP)(DDQ)(2)], and [(4BP)(TBCHD)] for the donor (4BP) and the acceptors I-2, DDQ and TBCHD. In the 4BP-TCNQ reaction, a short-lived CT complex is formed followed by rapid N-substitution by TCNQ forming the final reaction product 7,7,8-tricyano-8-benzylpiperidinylquinodimethane [TCBPQDM]. These products were isolated as solids and have been characterized through electronic and infrared spectra as well as elemental and thermal analysis measurements. The formation constants (K-CT), charge transfer energy (E-CT), molar extinction coefficients (epsilon(CT)), free energy change Delta G degrees and ionization potential I-P of the formed CT-complexes [(4BP)I](+) I-3(-) [(4BP)(DDQ)(2)] and [(4BP)(TBCHD)] were obtained. (C) 2013 Elsevier B.V. All rights reserved.