Topological features and electronic structure of 4-chloro-1H-pyrrolo[2,3-b]pyridine: experimental charge density analysis and DFT studies

Abstract

The experimental charge density distribution in 4-chloro-1H-pyrrolo[2,3-b]pyridine has been carried out using high resolution X-ray diffraction data collected at 100(2) K. Multipole refinement based on the Hansen–Coppens formalism coupled with an estimation of anisotropic displacement parameters (ADPs) of hydrogen atoms converged to R(F) = 0.0353 for 5700 reflections with I > 3σ(I) and sin θ/λ ≤ 1.08 Å⁻¹. The topology of the bonding scheme within the molecule as well as of the intermolecular N–H⋯N and C–H⋯Cl hydrogen bonds has been investigated. The covalent nature of N–C and C–C bonds in the pyrrolopyridine skeleton of the molecule has been established by (3, −1) bond critical points associated with relatively large electron densities [2.07(2)–2.74(3) e Å⁻³] and highly negative Laplacian values [−11.37(4) to −19.20(10) e Å⁻⁵]. The topological parameters corresponding to H⋯N and H⋯Cl critical points indicate a moderately strong intermolecular N–H⋯N hydrogen bond and a weak C–H⋯Cl closed-shell interaction. The electronic structure of the title compound has been calculated by density functional theory (DFT) at the BLYP level. A large HOMO–LUMO energy gap (3.59 eV; HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital) implies a high kinetic stability of the title compound.