Quantum-Chemical Search for Keto Tautomers of Azulenols in Vacuo and Aqueous Solution
<p>The structural differences between azulene (<b>a</b>) and naphthalene (<b>b</b>).</p> "> Figure 2
<p>Monohydroxyazulenes investigated in this work.</p> "> Figure 3
<p>The potential resonance structures for anions of hydroxyazulenes: <b>A<sup>−</sup>1</b> (<b>a</b>), <b>A<sup>−</sup>2</b> (<b>b</b>), <b>A<sup>−</sup>3</b> (<b>c</b>), <b>A<sup>−</sup>4</b> (<b>d</b>), and <b>A<sup>−</sup>5</b> (<b>e</b>).</p> "> Figure 3 Cont.
<p>The potential resonance structures for anions of hydroxyazulenes: <b>A<sup>−</sup>1</b> (<b>a</b>), <b>A<sup>−</sup>2</b> (<b>b</b>), <b>A<sup>−</sup>3</b> (<b>c</b>), <b>A<sup>−</sup>4</b> (<b>d</b>), and <b>A<sup>−</sup>5</b> (<b>e</b>).</p> "> Figure 4
<p>The DFT-calculated negative protonation energies (−<span class="html-italic">E</span><sub>prot</sub>, in kJ mol<sup>−1</sup>) for deprotonated azulenols. −<span class="html-italic">E</span><sub>prot</sub> for individual conjugated sites placed near O and C atoms.</p> "> Figure 5
<p>The structures of enol rotamers and possible keto tautomers of 1- (<b>a</b>), 2- (<b>b</b>), 4- (<b>c</b>), 5- (<b>d</b>), and 6-hydroxyazulene (<b>e</b>), and their relative electronic energies (∆<span class="html-italic">E</span> given in parentheses, in kJ mol<sup>−1</sup>) in vacuo (normal style) and aqueous solution (italic style).</p> "> Figure 5 Cont.
<p>The structures of enol rotamers and possible keto tautomers of 1- (<b>a</b>), 2- (<b>b</b>), 4- (<b>c</b>), 5- (<b>d</b>), and 6-hydroxyazulene (<b>e</b>), and their relative electronic energies (∆<span class="html-italic">E</span> given in parentheses, in kJ mol<sup>−1</sup>) in vacuo (normal style) and aqueous solution (italic style).</p> "> Figure 6
<p>Comparison of the harmonic oscillator model of electron delocalization (HOMED) indices estimated for the DFT structures of naphthalene (<b>a</b>), azulene (<b>b</b>), and single aromatic rings: benzene (<b>c</b>), cyclopentadiene anion (<b>d</b>), and cycloheptatriene cation (<b>e</b>). HOMEDs for the entire bicyclic molecule placed below structure and those for the single structural parts included in the ring.</p> "> Figure 7
<p>The HOMED indices estimates for unsubstituted azulene (structure 6) and for the five anionic forms A<sup>−</sup>1–A<sup>−</sup>5 (structures 1–5, respectively). HOMED5, HOMED7, HOMED11, and HOMED12 correspond to the five- and seven-membered rings, azulene system, and the entire molecule containing the CO bond.</p> "> Figure 8
<p>The linear relationships between the DFT-calculated C9C10 bond lengths (in Å) and HOMED5 indices for the anion forms and enol rotamers of hydroxyazulenes.</p> "> Figure 9
<p>Linear tendencies between the HOMED7 and HOMED5 indices for selected keto isomers of azulenols <b>AH1</b> and <b>AH4</b>.</p> "> Figure 10
<p>Linear tendencies between the HOMED12 indices and relative electronic energies (∆<span class="html-italic">E</span> in kJ mol<sup>−1</sup>) for all possible keto tautomers of azulenols <b>AH1</b><b>−AH5</b>.</p> "> Scheme 1
<p>The favored keto and enol tautomers for 1- (<b>a</b>), 2- (<b>b</b>), 4- (<b>c</b>), 5- (<b>d</b>), and 6-hydroxyazulene (<b>e</b>). HOMED5s and HOMED7s are placed in the rings. The percentages contents of isomers in vacuo and aqueous solution are included below structures.</p> ">
Abstract
:1. Introduction
2. Methodology
3. Results and Discussion
3.1. Deprotonated Forms of Hydroxyazulenes
3.2. Possible Keto and Enol Isomers of Hydroxyazulenes
3.3. Bonds Lengths Alternation in Neutral and Anionic Forms of Hydroxyazulenes
3.4. Favored Isomers for Hydroxyazulenes in Vacuo and Aqueous Solution
3.5. Acid-Base Properties for Selected Isomers and for Isomeric Mixtures
4. Conclusions
Supplementary Materials
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Structure | HOMED5 | HOMED7 | HOMED11 | HOMED12 |
---|---|---|---|---|
AH1a | 0.803 | 0.855 | 0.902 | 0.861 |
AH1b | 0.817 | 0.868 | 0.910 | 0.866 |
AH2a/AH2b | 0.832 | 0.871 | 0.913 | 0.882 |
AH3a | 0.865 | 0.903 | 0.932 | 0.895 |
AH3b | 0.852 | 0.896 | 0.928 | 0.888 |
AH4a | 0.812 | 0.864 | 0.908 | 0.851 |
AH4b | 0.806 | 0.860 | 0.904 | 0.848 |
AH5a/AH5b | 0.859 | 0.899 | 0.930 | 0.932 |
Isomer | Structure | HOMED5 | HOMED7 | HOMED11 | HOMED12 |
---|---|---|---|---|---|
C1H/C3H | AH2c/AH2d | 0.341 | 0.829 | 0.607 | 0.596 |
C1H | AH3c | 0.504 | 0.835 | 0.652 | 0.650 |
C3H | AH3e | 0.519 | 0.831 | 0.657 | 0.656 |
C1H | AH4c | 0.382 | 0.776 | 0.582 | 0.582 |
C3H | AH4d | 0.384 | 0.782 | 0.587 | 0.586 |
C1H/C3H | AH5c/AH5d | 0.495 | 0.814 | 0.634 | 0.632 |
C2H | AH1c | 0.232 | 0.768 | 0.520 | 0.504 |
C2H | AH3d | 0.509 | 0.638 | 0.583 | 0.596 |
C2H | AH5e | 0.504 | 0.625 | 0.575 | 0.571 |
C4H | AH1d | 0.361 | 0.635 | 0.460 | 0.444 |
C8H | AH1h | 0.343 | 0.641 | 0.456 | 0.443 |
C4H/C8 | AH2e/AH2f | 0.341 | 0.829 | 0.607 | 0.596 |
C4H | AH4e | 0.670 | 0.446 | 0.525 | 0.515 |
C8H | AH4g | 0.637 | 0.424 | 0.504 | 0.501 |
C5H | AH1e | 0.473 | 0.523 | 0.467 | 0.457 |
C7H | AH1g | 0.484 | 0.521 | 0.473 | 0.462 |
C5H | AH3f | 0.769 | 0.453 | 0.572 | 0.562 |
C7H | AH3g | 0.731 | 0.476 | 0.576 | 0.572 |
C5H/C7H | AH5f/AH5g | 0.774 | 0.459 | 0.572 | 0.564 |
C6H | AH1f | 0.374 | 0.626 | 0.454 | 0.440 |
C6H | AH2g | 0.396 | 0.471 | 0.485 | 0.475 |
C6H | AH4f | 0.794 | 0.390 | 0.570 | 0.558 |
C9H | AH1i | 0.250 | 0.578 | 0.470 | 0.458 |
C10H | AH1j | 0.229 | 0.575 | 0.449 | 0.440 |
C9H | AH3h | 0.513 | 0.480 | 0.534 | 0.529 |
C10H | AH3i | 0.457 | 0.418 | 0.468 | 0.467 |
C9H/C10H | AH5h/AH5i | 0.461 | 0.425 | 0.473 | 0.318 |
Structure | Type of Isomer | x | Structure | Type of Isomer | x | ||
---|---|---|---|---|---|---|---|
Gas 1 | Water 2 | Gas 1 | Water 2 | ||||
AH1a | OH(a) | 10.1 | 12.4 | AH3e | C3H | 0.5 | 0.05 |
AH1b | OH(b) | 89.6 | 87.6 | AH4a | OH(a) | 28.4 | 33.7 |
AH1c | C2H | 0.3 | 0.001 | AH4b | OH(b) | 29.0 | 41.9 |
AH2a/AH2b | OH(a)/OH(b) | 52.8 | 67.9 | AH4c | C1H | 9.2 | 7.8 |
AH2c/AH2d | C1H/C3H | 47.2 | 32.1 | AH4d | C3H | 33.4 | 16.5 |
AH3a | OH(a) | 89.4 | 7.5 | AH5a/AH5b | OH(a)/OH(b) | 99.5 | 99.96 |
AH3b | OH(b) | 9.5 | 92.4 | AH5c/AH5d | C1H/C3H | 0.5 | 0.04 |
AH3c | C1H | 0.7 | 0.1 |
Structure | Type of Isomer | PA(A−) = ∆acidH(AH) | GB(A−) = ∆acidG(AH) | Structure | Type of Isomer | PA(A−) = ∆acidH(AH) | GB(A−) = ∆acidG(AH) |
---|---|---|---|---|---|---|---|
AH1a | OH(a) | 1419.2 | 1385.8 | AH3e | C3H | 1369.5 | 1339.4 |
AH1b | OH(b) | 1420.4 | 1391.2 | AH4a | OH(a) | 1402.4 | 1370.8 |
AH1c | C2H | 1407.2 | 1377.0 | AH4b | OH(b) | 1402.6 | 1370.9 |
AH2a/AH2b | OH(a)/OH(b) | 1393.9 | 1362.5 | AH4c | C1H | 1398.4 | 1368.0 |
AH2c/AH2d | C1H/C3H | 1391.9 | 1362.2 | AH4d | C3H | 1401.7 | 1371.2 |
AH3a | OH(a) | 1383.1 | 1352.3 | AH5a/AH5b | OH(a)/OH(b) | 1371.0 | 1339.3 |
AH3b | OH(b) | 1378.3 | 1346.7 | AH5c/AH5d | C1H/C3H | 1355.3 | 1326.0 |
AH3c | C1H | 1370.1 | 1340.1 |
Compound | Mixture of the Favored Isomers for Neutral AH (Acid) 1 | Anion A− (Base) 2 | PA or ∆acidH | GB or ∆acidG | Ref. |
---|---|---|---|---|---|
1-Azulenol | AH1a ⇄ AH1b ⇄ AH1c | A−1 | 1420.3 | 1390.6 | 3 |
2-Azulenol | AH2a/AH2b ⇄ AH2c/AH2d | A−2 | 1393.0 | 1362.3 | 3 |
4-Azulenol | AH3a ⇄ AH3b ⇄ AH3c ⇄ AH3e | A−3 | 1382.5 | 1351.6 | 3 |
5-Azulenol | AH4a ⇄ AH4b ⇄ AH4c ⇄ AH4d | A−4 | 1401.8 | 1370.7 | 3 |
6-Azulenol | AH5a/AH2b ⇄ AH5c/AH5d | A−5 | 1370.9 | 1339.2 | 3 |
2-Naphthol 4 | 1438 | 1408 | 5 | ||
Phenol 4 | 1462 | 1432 | 5 |
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Raczyńska, E.D. Quantum-Chemical Search for Keto Tautomers of Azulenols in Vacuo and Aqueous Solution. Symmetry 2021, 13, 497. https://doi.org/10.3390/sym13030497
Raczyńska ED. Quantum-Chemical Search for Keto Tautomers of Azulenols in Vacuo and Aqueous Solution. Symmetry. 2021; 13(3):497. https://doi.org/10.3390/sym13030497
Chicago/Turabian StyleRaczyńska, Ewa D. 2021. "Quantum-Chemical Search for Keto Tautomers of Azulenols in Vacuo and Aqueous Solution" Symmetry 13, no. 3: 497. https://doi.org/10.3390/sym13030497