Structural Relevance of Intramolecular H-Bonding in <i>Ortho</i>-Hydroxyaryl Schiff Bases: The Case of 3-(5-bromo-2-hydroxybenzylideneamino) Phenol
A new Schiff base compound, 3-(5-bromo-2-hydroxybenzylideneamino)phenol (abbreviated as BHAP) was synthesized and characterized by <sup>1</sup>H- and <sup>13</sup>C- nuclear magnetic resonance and infrared spectroscopies. DFT/B3LYP/6-311++G(d,p) calculations were undertaken i...
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MDPI AG
2021-05-01
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| author | İsa Sıdır Yadigar Gülseven Sıdır Sándor Góbi Halil Berber Rui Fausto |
| author_facet | İsa Sıdır Yadigar Gülseven Sıdır Sándor Góbi Halil Berber Rui Fausto |
| author_sort | İsa Sıdır |
| collection | DOAJ |
| description | A new Schiff base compound, 3-(5-bromo-2-hydroxybenzylideneamino)phenol (abbreviated as BHAP) was synthesized and characterized by <sup>1</sup>H- and <sup>13</sup>C- 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 <i>E</i>- and <i>Z</i>- 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 <i>E</i>-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 (<i>E</i>-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 <i>o</i>-hydroxyaryl Schiff base compounds. |
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| last_indexed | 2024-03-10T11:34:29Z |
| publishDate | 2021-05-01 |
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| spelling | doaj.art-41cf44c9d4af4d59b8de20f04733430f2023-11-21T18:59:12ZengMDPI AGMolecules1420-30492021-05-01269281410.3390/molecules26092814Structural Relevance of Intramolecular H-Bonding in <i>Ortho</i>-Hydroxyaryl Schiff Bases: The Case of 3-(5-bromo-2-hydroxybenzylideneamino) Phenolİsa Sıdır0Yadigar Gülseven Sıdır1Sándor Góbi2Halil Berber3Rui Fausto4Department of Physics, Faculty of Science and Arts, Bitlis Eren University, 13000 Bitlis, TurkeyDepartment of Physics, Faculty of Science and Arts, Bitlis Eren University, 13000 Bitlis, TurkeyCQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, PortugalDepartment of Chemistry, Faculty of Science, Eskişehir Technical University, 26470 Eskişehir, TurkeyCQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, PortugalA new Schiff base compound, 3-(5-bromo-2-hydroxybenzylideneamino)phenol (abbreviated as BHAP) was synthesized and characterized by <sup>1</sup>H- and <sup>13</sup>C- 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 <i>E</i>- and <i>Z</i>- 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 <i>E</i>-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 (<i>E</i>-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 <i>o</i>-hydroxyaryl Schiff base compounds.https://www.mdpi.com/1420-3049/26/9/2814Schiff baseconformational spacematrix isolation infrared spectroscopyintramolecular hydrogen bondingDFT/B3LYP/6-311++G(d,p) calculationsquantum mechanical tunneling |
| spellingShingle | İsa Sıdır Yadigar Gülseven Sıdır Sándor Góbi Halil Berber Rui Fausto Structural Relevance of Intramolecular H-Bonding in <i>Ortho</i>-Hydroxyaryl Schiff Bases: The Case of 3-(5-bromo-2-hydroxybenzylideneamino) Phenol Molecules Schiff base conformational space matrix isolation infrared spectroscopy intramolecular hydrogen bonding DFT/B3LYP/6-311++G(d,p) calculations quantum mechanical tunneling |
| title | Structural Relevance of Intramolecular H-Bonding in <i>Ortho</i>-Hydroxyaryl Schiff Bases: The Case of 3-(5-bromo-2-hydroxybenzylideneamino) Phenol |
| title_full | Structural Relevance of Intramolecular H-Bonding in <i>Ortho</i>-Hydroxyaryl Schiff Bases: The Case of 3-(5-bromo-2-hydroxybenzylideneamino) Phenol |
| title_fullStr | Structural Relevance of Intramolecular H-Bonding in <i>Ortho</i>-Hydroxyaryl Schiff Bases: The Case of 3-(5-bromo-2-hydroxybenzylideneamino) Phenol |
| title_full_unstemmed | Structural Relevance of Intramolecular H-Bonding in <i>Ortho</i>-Hydroxyaryl Schiff Bases: The Case of 3-(5-bromo-2-hydroxybenzylideneamino) Phenol |
| title_short | Structural Relevance of Intramolecular H-Bonding in <i>Ortho</i>-Hydroxyaryl Schiff Bases: The Case of 3-(5-bromo-2-hydroxybenzylideneamino) Phenol |
| title_sort | structural relevance of intramolecular h bonding in i ortho i hydroxyaryl schiff bases the case of 3 5 bromo 2 hydroxybenzylideneamino phenol |
| topic | Schiff base conformational space matrix isolation infrared spectroscopy intramolecular hydrogen bonding DFT/B3LYP/6-311++G(d,p) calculations quantum mechanical tunneling |
| url | https://www.mdpi.com/1420-3049/26/9/2814 |
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