Spectroscopic and theoretical studies on the monomeric and dimeric forms of methyl pyrrole-2-carboxylate

Abstract

The infrared spectra of a very dilute solution and a KBr pellet of methyl pyrrole-2-carboxylate (MPC) are compared with the theoretical spectra of monomeric and dimeric forms of MPC obtained at the RHF/6-311+G^* level of theory, showing that dimers connected through N–H⋯O interactions are dominant in the solid state. Ab initio calculations are used for the analysis of geometries of both monomeric and dimeric forms of MPC. The H-bond energy for MPC dimer is calculated and the basis set superposition error (BSSE) is corrected by the counterpoise method of Boys and Bernardi. The Bader theory is also used to analyse N–H⋯O interactions within the MPC dimer. The experimental IR spectra, results of ab initio calculations and the analysis of topological parameters obtained from the Bader theory show that H-bonds of MPC dimer are of medium strength. The N–H⋯O interactions of MPC are also compared with a sample of other conventional and unconventional H-bonds and a measure of the H-bond strength introduced recently is applied in this study.