Infrared, density-functional theory, and atoms in molecules method studies on conformers of some 2-substituted 1H-pyrroles

Methyl pyrrole-2-carboxylate (MPC), pyrrole-2-carbaldehyde (PC), methyl N-methylpyrrole-2-carboxylate (MPC-NMe), and N-methylpyrrole-2-carbaldehyde (PC-NMe) are investigated. Experimental and theoretical IR spectra and density-functional theory calculations concerning energetic and geometrical properties of molecular structures show that for all species s-cis conformers are more stable than s-trans ones. The existence of intramolecular N-(HO)-O-... hydrogen bonds for s-cis conformers of MPC and PC is controversial; the topological analysis based on Bader theory shows that such hydrogen bonds do not exist.