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 σ-acceptor iodine and π-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]+I3-, [(4BP)(DDQ)₂], and [(4BP)(TBCHD)] for the donor (4BP) and the acceptors I₂, 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 (ε_CT), free energy change ΔG^° and ionization potential I_P of the formed CT-complexes [^(4BP)I]+I3-, [(4BP)(DDQ)₂] and [(4BP)(TBCHD)] were obtained.