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Title: | Structural Relevance of Intramolecular H-Bonding in Ortho-Hydroxyaryl Schiff Bases: The Case of 3-(5-bromo-2-hydroxybenzylideneamino) Phenol | Authors: | Sıdır, İsa Gülseven Sıdır, Yadigar Góbi, Sándor Berber, Halil Fausto, Rui |
Keywords: | Schiff base; conformational space; matrix isolation infrared spectroscopy; intramolecular hydrogen bonding; DFT/B3LYP/6-311++G(d,p) calculations; quantum mechanical tunneling; NBO analysis | Issue Date: | 10-May-2021 | Project: | Bitlis Eren University Research Foundation for the financial support (Project BEBAP-2013.05) Erasmus Offices of the Bitlis Eren and Coimbra Universities - short term ERASMUS+ Grants at the University of Coimbra UI0313B/QUI/2020 UI0313P/QUI/2020 PTDC/QUI-QFI/1880/2020 |
Serial title, monograph or event: | Molecules | Volume: | 26 | Issue: | 9 | Abstract: | A new Schiff base compound, 3-(5-bromo-2-hydroxybenzylideneamino)phenol (abbreviated as BHAP) was synthesized and characterized by 1H- and 13C- nuclear magnetic resonance and infrared spectroscopies. DFT/B3LYP/6-311++G(d,p) calculations were undertaken in order to explore the conformational space of both the E- and Z- geometrical isomers of the enol-imine and keto-amine tautomers of the compound. Optimized geometries and relative energies were obtained, and it was shown that the most stable species is the E-enol-imine form, which may exist in four low-energy intramolecularly hydrogen-bonded forms (I, II, V, and VI) that are almost isoenergetic. These conformers were concluded to exist in the gas phase equilibrium with nearly equal populations. On the other hand, the infrared spectra of the compound isolated in a cryogenic argon matrix (10 K) are compatible with the presence in the matrix of only two of these conformers (conformers II and V), while conformers I and VI convert to these ones by quantum mechanical tunneling through the barrier associated with the rotation of the OH phenolic group around the C-O bond. The matrix isolation infrared spectrum was then assigned and interpreted with help of the DFT(B3LYP)/6-311++G(d,p) calculated infrared spectra for conformers II and V. In addition, natural bond orbital (NBO) analysis was performed on the most stable conformer of the experimentally relevant isomeric form (E-enol-imino conformer V) to shed light on details of its electronic structure. This investigation stresses the fundamental structural relevance of the O-H···N intramolecular H-bond in o-hydroxyaryl Schiff base compounds. | URI: | https://hdl.handle.net/10316/105264 | ISSN: | 1420-3049 | DOI: | 10.3390/molecules26092814 | Rights: | openAccess |
Appears in Collections: | FCTUC Química - Artigos em Revistas Internacionais |
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