Vibrational-electronic properties of intra/inter molecular hydrogen bonded heterocyclic dimer: An experimental and theoretical study of pyrrole-2-carboxaldehyde

Abstract

Vibrational and electronic characteristics of pyrrole-2-carboxaldehyde (PCL) are used to establish the existence of dimeric form in solid phase and monomeric form in solution phase. PCL can exist in both monomeric and dimeric forms. Experimental and computed results using Density Functional Theory (DFT) (energy, dipole moment, Gibbs energy, FTIR, Raman, UV–vis and electrical conductivity) favor the existence of cis dimer (C_d) form. Natural Bond Orbital (NBOs) analysis also provides the signature of strong intermolecular hydrogen bonding (I_erHB) as the possible reason for the existence of Cd in solid phase. Different vibrational modes (ν_NH, ν_CO, etc.) also establish the existence of monomeric form (C) of PCL in its solution phase. In the solid phase, the proton hopping through I_erHB within C_d validates the existence of dimeric form of PCL.