Hydrogen Bonding in Crystals of Pyrrol-2-yl Chloromethyl Ketone Derivatives and Methyl Pyrrole-2-Carboxylate

Abstract

The crystal and molecular structure of three derivatives of carbonyl 2-substituted pyrroles was determined by the single crystal X-ray diffraction. There are 2,2-dichloro-1-(1-methyl-1H-pyrrol-2-yl)ethan-1-one (I), 2-chloro-1-(1H-pyrrol-2-yl)ethan-1-one (II) and methyl 1H-pyrrole-2-carboxylate (III). All compounds crystallize with one molecule in the asymmetric unit in P212121 for I and II, and P21/c group for III. Despite the similar structures of the investigated compounds, the hydrogen bonds formed in their crystal structures adopt different H-bond motifs. In structure I, the dimers R12(5) and R21(7) form a chain along the b-axis, while in structures II and III, chain C(5) structural motifs are formed. The single point calculations at a ωB97XD/6-311++G(d,p) level of theory indicate that systems with N-H⋯O bonds have greater interaction energies (are more stable) compared with systems featuring C-H⋯O/Cl bonds. A descriptive Hirshfeld analysis showed that the greatest differences are visible for the H⋯H interactions. These H⋯H interactions predominate in structure III, accounting for 45% of the intermolecular interactions, while in structures I and II, they account for only 25%. Although compounds I-II contain Cl-atoms, the percentage of Cl⋯Cl interactions is rather low. In structure with two Cl-atoms (I), the contribution of the Cl⋯Cl contacts is 8.7% and for II, the contribution accounts for only 0.4% of the interactions.