Nitroso-oxime tautomerism in nitroso pyrroles: Revealing spectral properties and crystalline structure
Year: 2025
Type: article
Abstract: Tautomerism plays a fundamental role in chemical reactivity, molecular recognition, and hydrogen bonding networks, influencing the stability and properties of many functional molecules. Among the various tautomeric equilibria, the nitroso-oxime interconversion has been poorly studied. In this work, a series of nine α-nitroso pyrroles containing thienyl moieties have been synthesized, characterized and studied by spectroscopic and crystallographic techniques. Tautomerism was evidenced by variable-low temperature 1H NMR experiments. In addition, the crystallographic data of seven of them and four precursor pyrroles, allowed a comparative analysis of the supramolecular interactions in these heterocycles. Analysis of pyrroles revealed that N-H···S, S···π, C-H···π, and Br···Br interactions were responsible of crystal structure stability, whereas the α-nitroso pyrroles crystallize in centrosymmetric space groups with different arrangements. Notably, five of the nitroso derivatives revealed a centrosymmetric N-H···O (2.08 Å) hydrogen bond leading to an R22(10) dimeric synthon. Interestingly, two of the nitroso pyrroles crystallized in their oxime tautomeric form, as evidenced by a significantly shorter Cipso–Nnitroso (1.297 Å) bond and an elongated N–O bond (1.368 Å), in contrast to the nitroso tautomeric forms (C–N: 1.341 Å, N–O: 1.268 Å). Cooperative strong O-H···N hydrogen bonds give rise to an intriguing R44(20) tetrameric synthon in the asymmetric unit for the oxime tautomeric forms. This study underscores how supramolecular synthons influence tautomerism in heterocyclic systems, offering valuable insights into the cooperative nature of hydrogen bonding. These results redefine the structural landscape of nitroso-pyrroles and open new perspectives for their reactivity and potential applications in organic synthesis and materials science.
Source: Journal of Molecular Structure
Language: English
Subfield: Physical and Theoretical Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,360
OpenAlex ID: W4411125831