Theoretical and experimental examinations to substantiate the structure of coal derived asphaltene by formation of complex with o-chloranil

Abstract

The structure of coal derived asphaltene (CDA) proposed by Mullins et al has been corroborated through theoretical and experimental examination by the virtue of its electron donor property. Here, o-chloranil has been used as an electron acceptor. Investigation of o-chloranil/CDA complex in gas phase has been performed by density functional theory (DFT) methods. The Charge transfer (CT) transition energy of the complex in gas phase was calculated by the time-dependent density function theory (TD-DFT) using the ground state optimized geometry at the respective levels of theory. For this, the three semi empirical methods AM1, PM3 and PM3MM were computed under the MPW1PW91, B3PW91, PBE1PBE, BPV86 and RCIS formalism. It is found that the two formalisms MPW1PW91 and PBEPBE under PM3 and PM3MM reproduced values close to the experimental one. However, all of them provide lower charge transfer (CT) transition energy values than that has been experimentally determined. Experimentally, FTIR spectra of the donor, acceptor and the complex further supported the understanding of complex formation and demonstrated close similarity with the theoretically determined CDA frequencies. These findings support the validity of the CDA structure to an extent.