Crystal and Molecular Structure of Pyrrole-2-carboxylic Acid; π-Electron Delocalization of Its Dimers−DFT and MP2 Calculations

Abstract

The crystal and molecular structure of pyrrole-2-carboxylic acid (PCA) determined by single-crystal X-ray diffraction is presented. Intermolecular H-bonds for this structure are analyzed. The DFT calculations at the B3LYP/6-311++G(d,p) level of theory and ab initio calculations at the MP2/6-311++G(d,p) level are performed for dimers of pyrrole-2-carboxylic acid and for similar model species. The X-ray data and calculations show that the pyrrole moiety within pyrrole-2-carboxylic acid influences the π-electron delocalization and hence the strength of the hydrogen bonds. The geometrical and energetic features of H-bonds of PCA dimers and of model complexes are analyzed. Additionally, the Bader theory is applied, and the characteristics of the bond critical points and ring critical points confirm the influence of the pyrrole moiety on the strength of H-bond interactions.