Molecular tailoring approach as tool for revealing resonance‐assisted hydrogen bond: Case study of Z‐pyrrolylenones with the NH⋯OС intramolecular hydrogen bond

• Published in: Journal of computational chemistry Vol. 43; no. 23; pp. 1596 - 1607
• Main Authors: Afonin, Andrei V., Rusinska‐Roszak, Danuta
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 05.09.2022; Wiley Subscription Services, Inc
• Subjects: Aromaticity; Bond energy; Chemical bonds; decomposition energy into components; Energy; function‐based approach; Hydrogen bonding; Hydrogen bonds; Hydrogen-based energy; intramolecular hydrogen bond energy; Isomers; molecular tailoring approach; pyrrolylenones; Resonance; resonance‐assisted hydrogen bond
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.26960

Both the experimental and calculated data reveal that a strong NH⋯OС intramolecular hydrogen bond closing the seven‐membered quasi‐cycle is formed in the Z‐isomers of pyrrolylenones. Comparison of the NH⋯OС intramolecular hydrogen bonds energies in the pyrrolylenones, estimated via the molecular tailoring approach, with the similar data for reference malonaldehydes shows that the resonance‐assisted hydrogen bonding occurs in both cases, the hydrogen bond energy being varied mainly within 10–20 kcal/mol. The combined application of function‐based and molecular tailoring approaches makes it possible to decompose the NH⋯OС total hydrogen bond energy in the pyrrolylenones into the π‐ and σ‐components. It is established that the contribution of the π‐component to the total N(O)H⋯OС hydrogen bond energy in the pyrrolylenones and malonaldehydes is almost the same (6–7 kcal/mol). Comparison of the π‐contribution to the total energy of the resonance‐assisted hydrogen bonding in the Z‐isomer of pyrrolylenones with the energy of the push‐pull effect in the E‐isomer of pyrrolylenones reveals that the resonance contribution to the total energy of the resonance‐assisted hydrogen bond in the former significantly enhances with reference to the net resonance energy in the latter. The appearance of the resonance‐assisted hydrogen bond in the pyrrolylenones is possible due to the participation in the interaction of 10 or 14 π‐electrons satisfying the Hückel aromaticity rule. The energies of NH⋯OС intramolecular hydrogen bond in the series of Z‐pyrrolylenones are quantified via molecular tailoring approach. Comparing these energies with those of OH⋯OС intramolecular hydrogen bond in the series of malonaldehydes as RAHB structures, on the one hand, and the hydroxycarbonyl aliphatic compounds as non‐RAHB structures, on the other hand, shows that the pyrrolylenoes are like to the former structures rather than the latter ones.