NMR analysis of a series of 1,2-bis(1-R-5-oxo-2,3-dihydro-1H-pyrrol-4-ylidene)ethanes and X-ray crystal structure analysis of theR= mesityl compound

Abstract

Four tetramethyl 4,4′-(ethane-1,2-diylidene)bis[1-R-5-oxo-4,5-dihydro-1H-pyrrole-2,3-dicarboxylate] compounds, denoted class (1), are a series of conjugated buta-1,3-dienes substituted with a heterocyclic group. The compounds can be used as dyes and pigments due to their long-range conjugated systems. Four structures were studied using1H NMR,13C NMR and mass spectroscopy,viz.withR= 2,4,6-trimethylphenyl, (1a),R = cyclohexyl, (1b),R=tert-butyl, (1c), andR= isopropyl, (1d). A detailed discussion is presented regarding the characteristics of the three-dimensional structures based on NMR analysis and the X-ray crystal structure of (1a), namely tetramethyl 4,4′-(ethane-1,2-diylidene)bis[5-oxo-1-(2,4,6-trimethylphenyl)-4,5-dihydro-1H-pyrrole-2,3-dicarboxylate], C36H36N2O10. The conjugation plane and stability were also studiedviaquantum chemical calculations.