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Jarończyk M, Ostrowski S, Dobrowolski JC. On Integral INICS Aromaticity of Pyridodiazepine Constitutional Isomers and Tautomers. Molecules 2023; 28:5684. [PMID: 37570653 PMCID: PMC10419959 DOI: 10.3390/molecules28155684] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Revised: 07/24/2023] [Accepted: 07/25/2023] [Indexed: 08/13/2023] Open
Abstract
The structure, energetics, and aromaticity of c.a. 100 constitutional isomers and tautomers of pyrido[m,n]diazepines (m = 1, 2; n = 2, 3, 4, 5; m ≠ n) were studied at the B3LYP/cc-pVTZ level. The pyrido[1,3]diazepines appear the most, while pyrido[2,4]diazepines are the least stable (ca. 26 kcal/mol). In the pyrido[1,n]diazepine group (n = 2-5), the [1,5] isomers are higher in energy by ca. 4.5 kcal/mol and the [1,4] ones by ca. 7 kcal/mol, and the pyrido[1,2]diazepines are the least stable (ca. 20 kcal/mol). All the most stable pyrido[1,n]diazepines have N-atoms near the ring's junction bond but on opposite sites. The most stable [2,n]-forms are also those with the pyridine ring N6-atom near the junction bond. Surprisingly, for the [1,2]-, [1,3]-, and [1,4]-isomer condensation types of pyridine and diazepine rings, the same N9 > N7 > N6 > N8 stability pattern obeys. The stability remains similar in a water medium simulated with the Polarizable Continuum Model of the solvent and is conserved when calculated using the CAM-B3LYP or BHandHlyp functionals. The ring's aromaticity in the pyridine[m,n]diazepines was established based on the integral INICS index resulting from the NICSzz-scan curves' integration. The integral INICS index is physically justified through its relation to the ringcurrent as demonstrated by Berger, R.J.F., et al. Phys. Chem. Chem. Phys. 2022, 24, 624. The six-membered pyrido rings have negative INICSZZ indices and can be aromatic only if they are not protonated at the N-atom. All protonated pyrido and seven-membered rings exhibit meaningful positive INICSZZ values and can be assigned as antiaromatic. However, some non-protonated pyrido rings also have substantial positive INICSZZ indices and are antiaromatic. A weak linear correlation (R2 = 0.72) between the INICSZZ values of the pyridine I(6) and diazepine I(7) rings exists and is a consequence of the communication between the π-electron systems of the two rings. The juxtaposition of the INICS descriptor of the six- and seven-membered rings and diverse electron density parameters at the Ring Critical Points (RCP) revealed good correlations only with the Electrostatic Potentials from the electrons and nuclei (ESPe and ESPn). The relationships with other RCP parameters like electron density and its Laplacian, total energy, and the Hamiltonian form of kinetic energy density were split into two parts: one nearly constant for the six-membered rings and one linearly correlating for the seven-membered rings. Thus, most of the electron density parameters at the RCP of the six-membered rings of pyridodiazepines practically do not change with the diazepine type and the labile proton position. In contrast, those of the seven-membered rings display aromaticity changes in the antiaromatic diazepine with its ring structural modifications.
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Affiliation(s)
| | - Sławomir Ostrowski
- Institute of Chemistry and Nuclear Technology, 16 Dorodna Street, 03-195 Warsaw, Poland;
| | - Jan Cz. Dobrowolski
- National Medicines Institute, 30/34 Chełmska Street, 00-725 Warsaw, Poland
- Institute of Chemistry and Nuclear Technology, 16 Dorodna Street, 03-195 Warsaw, Poland;
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Bianchi P, Monbaliu JCM. Three decades of unveiling the complex chemistry of C-nitroso species with computational chemistry. Org Chem Front 2022. [DOI: 10.1039/d1qo01415c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This review revisits the complex reactivity of C-nitroso derivatives through the synergistic combination of computational and synthetic organic chemistry, with an emphasis on the rationalization of mechanisms and selectivities.
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Affiliation(s)
- Pauline Bianchi
- Center for Integrated Technology and Organic Synthesis, MolSys Research Unit, University of Liège, B-4000 Liège (Sart Tilman), Belgium
| | - Jean-Christophe M. Monbaliu
- Center for Integrated Technology and Organic Synthesis, MolSys Research Unit, University of Liège, B-4000 Liège (Sart Tilman), Belgium
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Application of the Extended HOMED (Harmonic Oscillator Model of Aromaticity) Index to Simple and Tautomeric Five-Membered Heteroaromatic Cycles with C, N, O, P, and S Atoms. Symmetry (Basel) 2019. [DOI: 10.3390/sym11020146] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The geometry-based HOMA (Harmonic Oscillator Model of Aromaticity) descriptor, based on the reference compounds of different delocalizations of n- and π-electrons, can be applied to molecules possessing analogous bonds, e.g., only CC, only CN, only CO, etc. For compounds with different heteroatoms and a different number of CC, CX, XX, and XY bonds, its application leads to some discrepancies. For this reason, the structural descriptor was modified and the HOMED (Harmonic Oscillator Model of Electron Delocalization) index defined. In 2010, the HOMED index was parameterized for compounds with C, N and O atoms. For parametrization, the reference molecules of similar delocalizations of n- and π-electrons were employed. In this paper, the HOMED index was extended to compounds containing the CP, CS, NN, NP, PP, NO, NS, PO, and PS bonds. For geometrical optimization of all reference molecules and of all investigated heterocompounds, the same quantum–chemical method {B3LYP/6-311+G(d,p)} was used to eliminate errors of the HOMED estimation. For some tautomeric systems, the Gn methods were also employed to confirm tautomeric preferences. The extended HOMED index was applied to five-membered heterocycles, simple furan and thiophene, and their N and P derivatives as well as for tautomeric pyrrole and phosphole and their N and P derivatives. The effects of additional heteroatom(s) in the ring on the HOMED values for furan are parallel to those for thiophene. For pyrroles, aromaticity dictates the tautomeric preferences. An additional N atom in the ring only slightly affects the HOMED values for the favored and well delocalized NH tautomers. Significant changes take place for their rare CH forms. When intramolecular proton-transfer is considered for phosphole and its P derivatives, the PH tautomers seem to be favored only for 1,2,3-triphosphole/1,2,5-triphosphole and for 1,2,3,5-tetraphosphole. For other phospholes, the CH forms have smaller Gibbs energies than the PH isomers. For phosphazoles, the labile proton in the favored form is linked to the N atom. The PH forms have smaller HOMED indices than the NH tautomers but higher than the CH ones.
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Theoretical investigation of reaction kinetics and thermodynamics of the keto-enol tautomerism of 1, 3, 5-triazin-2, 4(1H, 3H)-dione and its substituted systems utilizing density functional theory and transition state theory methods. COMPUT THEOR CHEM 2018. [DOI: 10.1016/j.comptc.2018.08.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Theoretical and vibrational spectroscopic approach to keto-enol tautomerism in methyl-2-(4-methoxybenzoyl)-3-(4-methoxyphenyl)-3-oxopropanoylcarbamate. J Mol Struct 2016. [DOI: 10.1016/j.molstruc.2016.05.060] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Mehr SHM, Patrick BO, MacLachlan MJ. Stabilization of a Strained Heteroradialene by Peripheral Electron Delocalization. Org Lett 2016; 18:1840-3. [DOI: 10.1021/acs.orglett.6b00577] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- S. Hessam M. Mehr
- Department of Chemistry, University of British Columbia, 2036
Main Mall, Vancouver, BC V6T 1Z1, Canada
| | - Brian O. Patrick
- Department of Chemistry, University of British Columbia, 2036
Main Mall, Vancouver, BC V6T 1Z1, Canada
| | - Mark J. MacLachlan
- Department of Chemistry, University of British Columbia, 2036
Main Mall, Vancouver, BC V6T 1Z1, Canada
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Krygowski TM, Szatylowicz H, Stasyuk OA, Dominikowska J, Palusiak M. Aromaticity from the viewpoint of molecular geometry: application to planar systems. Chem Rev 2014; 114:6383-422. [PMID: 24779633 DOI: 10.1021/cr400252h] [Citation(s) in RCA: 366] [Impact Index Per Article: 36.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Tadeusz M Krygowski
- Department of Chemistry, Warsaw University , Pasteura 1, 02-093 Warsaw, Poland
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Ortegón-Reyna D, Garcías-Morales C, Padilla-Martínez I, García-Báez E, Aríza-Castolo A, Peraza-Campos A, Martínez-Martínez F. NMR structural study of the prototropic equilibrium in solution of Schiff bases as model compounds. Molecules 2013; 19:459-81. [PMID: 24384925 PMCID: PMC6271073 DOI: 10.3390/molecules19010459] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2013] [Revised: 12/12/2013] [Accepted: 12/13/2013] [Indexed: 11/16/2022] Open
Abstract
An NMR titration method has been used to simultaneously measure the acid dissociation constant (pKa) and the intramolecular NHO prototropic constant ΔKNHO on a set of Schiff bases. The model compounds were synthesized from benzylamine and substituted ortho-hydroxyaldehydes, appropriately substituted with electron-donating and electron-withdrawing groups to modulate the acidity of the intramolecular NHO hydrogen bond. The structure in solution was established by 1H-, 13C- and 15N-NMR spectroscopy. The physicochemical parameters of the intramolecular NHO hydrogen bond (pKa, ΔKNHO and ΔΔG°) were obtained from 1H-NMR titration data and pH measurements. The Henderson-Hasselbalch data analysis indicated that the systems are weakly acidic, and the predominant NHO equilibrium was established using Polster-Lachmann δ-diagram analysis and Perrin model data linearization.
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Affiliation(s)
- David Ortegón-Reyna
- Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico.
| | - Cesar Garcías-Morales
- Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico.
| | - Itzia Padilla-Martínez
- Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico.
| | - Efren García-Báez
- Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico.
| | - Armando Aríza-Castolo
- Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico.
| | - Ana Peraza-Campos
- Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico.
| | - Francisco Martínez-Martínez
- Laboratorio de Posgrado, Facultad de Ciencias Químicas, Universidad de Colima, Km 9 Carretera Colima-Coquimatlán, Colima 28400, Mexico.
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Design of molecular switching and signaling based on proton transfer in 2-hydroxy Schiff bases: a computational study. J Mol Model 2012; 19:559-69. [DOI: 10.1007/s00894-012-1578-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Accepted: 08/20/2012] [Indexed: 11/24/2022]
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12
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Martyniak A, Majerz I, Filarowski A. Peculiarities of quasi-aromatic hydrogen bonding. RSC Adv 2012. [DOI: 10.1039/c2ra20846f] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Martyniak A, Lipkowski P, Boens N, Filarowski A. Electron-topological, energetic and π-electron delocalization analysis of ketoenamine-enolimine tautomeric equilibrium. J Mol Model 2012; 18:257-63. [PMID: 21523531 PMCID: PMC3249559 DOI: 10.1007/s00894-011-1075-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2010] [Accepted: 03/28/2011] [Indexed: 11/30/2022]
Abstract
The ketoenamine-enolimine tautometic equilibrium has been studied by the analysis of aromaticity and electron-topological parameters. The influence of substituents on the energy of the transition state and of the tautomeric forms has been investigated for different positions of chelate chain. The quantum theory of atoms in molecules method (QTAIM) has been applied to study changes in the electron-topological parameters of the molecule with respect to the tautomeric equilibrium in intramolecular hydrogen bond. Dependencies of the HOMA aromaticity index and electron density at the critical points defining aromaticity and electronic state of the chelate chain on the transition state (TS), OH and HN tautomeric forms have been obtained.
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Affiliation(s)
- Agata Martyniak
- Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie str., 50–383 Wrocław, Poland
| | - Pawel Lipkowski
- Theoretical Chemistry Group, Institute of Physical and Theoretical Chemistry, Wrocław University of Technology, Wyb. Wyspiańskiego 27, 50–370 Wrocław, Poland
| | - Noel Boens
- Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200f – bus 02404, 3001 Leuven, Belgium
| | - Aleksander Filarowski
- Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie str., 50–383 Wrocław, Poland
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Soltani Rad MN, Asrari Z, Behrouz S, Hakimelahi GH, Khalafi-Nezhad A. ‘Click Synthesis’ of 1H-1,2,3-Triazolyl-Based Oxiconazole (=(1Z)-1-(2,4-Dichlorophenyl)-2-(1H-imidazol-1-yl)ethanone O-[(2,4-Dichlorophenyl)methyl]oxime) Analogs. Helv Chim Acta 2011. [DOI: 10.1002/hlca.201100189] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Theoretical investigations on the structure and relative stabilities of the tautomeric forms of 6-amino-5-nitrosouracil and violuric acid derivatives (PM3-COSMO calculation). COMPUT THEOR CHEM 2011. [DOI: 10.1016/j.comptc.2010.12.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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17
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Rad MNS, Khalafi-Nezhad A, Behrouz S, Amini Z, Behrouz M. A Simple and Highly Efficient One-Pot Procedure for the Synthesis of Amides via Beckmann Rearrangements Using 1-Tosylimidazole (TsIm). PHOSPHORUS SULFUR 2010. [DOI: 10.1080/10426500903176554] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
| | - Ali Khalafi-Nezhad
- b Department of Chemistry , College of Sciences, Shiraz University , Shiraz, Iran
| | - Somayeh Behrouz
- b Department of Chemistry , College of Sciences, Shiraz University , Shiraz, Iran
| | - Zohreh Amini
- a Department of Chemistry , Faculty of Basic Sciences, Shiraz University of Technology , Shiraz, Iran
| | - Marzieh Behrouz
- b Department of Chemistry , College of Sciences, Shiraz University , Shiraz, Iran
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18
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On the Harmonic Oscillator Model of Electron Delocalization (HOMED) Index and its Application to Heteroatomic π-Electron Systems. Symmetry (Basel) 2010. [DOI: 10.3390/sym2031485] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
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19
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Conformational diversity of anthracycline anticancer antibiotics: A density functional theory calculation. ACTA ACUST UNITED AC 2010. [DOI: 10.1016/j.theochem.2010.04.008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Raczyńska ED, Zientara K, Stępniewski TM, Kolczyńska K. Stability, polarity, intramolecular interactions and π-electron delocalization for all eighteen tautomers rotamers of uracil. DFT studies in the gas phase. ACTA ACUST UNITED AC 2009. [DOI: 10.1135/cccc2008149] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Complete tautomeric equilibria were investigated for uracil at the DFT(B3LYP)/6-311+G(d,p) level to establish the stability order of all possible 18 tautomers-rotamers in the gas phase and to characterize their internal effects, polarity and aromatic character. Although the di-NH form strongly predominates (100%) in the mixture, the NH–OH, di-OH and CH–NH forms can be also considered. The favored tautomer is moderately stabilized by intramolecular interactions (attractions of the NH and C=O groups); it is also moderately polar and moderately delocalized. Stability of the functional groups (both amide functions) seems to be more important than intramolecular interactions, polarity and aromaticity. This is probably the main factor that dictates the tautomeric preferences in the uracil molecule.
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Filarowski A, Kochel A, Kluba M, Kamounah FS. Structural and aromatic aspects of tautomeric equilibrium in hydroxy aryl Schiff bases. J PHYS ORG CHEM 2008. [DOI: 10.1002/poc.1403] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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22
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Kluba M, Lipkowski P, Filarowski A. Theoretical investigation of tautomeric equilibrium in ortho-hydroxy phenyl Schiff bases. Chem Phys Lett 2008. [DOI: 10.1016/j.cplett.2008.08.076] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Filarowski A, Majerz I. AIM Analysis of Intramolecular Hydrogen Bonding in O-Hydroxy Aryl Schiff Bases. J Phys Chem A 2008; 112:3119-26. [DOI: 10.1021/jp076253x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- A. Filarowski
- Faculty of Chemistry, University of Wrocław 14 F. Joliot-Curie str., 50-383 Wrocław, Poland
| | - I. Majerz
- Faculty of Chemistry, University of Wrocław 14 F. Joliot-Curie str., 50-383 Wrocław, Poland
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24
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The proton transfer reaction in malonaldehyde derivatives: Substituent effects and quasi-aromaticity of the proton bridge. Chem Phys 2007. [DOI: 10.1016/j.chemphys.2007.09.016] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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25
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Sanz P, Mó O, Yáñez M, Elguero J. Non-resonance-assisted hydrogen bonding in hydroxymethylene and aminomethylene cyclobutanones and cyclobutenones and their nitrogen counterparts. Chemphyschem 2007; 8:1950-8. [PMID: 17676647 DOI: 10.1002/cphc.200700266] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The characteristics of intramolecular hydrogen bonds (IMHB) have been systematically analyzed for a series of 32 different enols of derivatives of cyclobutane, cyclobutene, and cyclobutadiene bearing oxygen and nitrogen functionalities, at the B3LYP/6-311+G(3df,2p)//B3LYP/6-311+G(d,p) level of theory. In those cases where two tautomers (interconnected by a hydrogen shift through the IMHB) exist, tautomer a, in which the HB-donor group (YH) is attached to the four-membered ring, is less stable than tautomer b, in which is the HB-acceptor (X) is the one attached to the four-membered ring. As expected the OH group behaves as a better HB-donor than the NH(2) group and the C==NH group as a better HB-acceptor than the C==O group, although the first effect clearly dominates. Accordingly, the expected IMHB strength follows the [donor, acceptor] trend: [OH,C==NH]>[OH,C==O]>[NH(2),C==NH]>[NH(2),C==O]. Quite unexpectedly, in all those compounds in which the functionality exhibiting the IMHB is unsaturated, the IMHB is weaker than in their saturated counterparts, verifying that the primary effect on the strength of the IMHB is the structure of the sigma-skeleton of the system. In the conjugated systems investigated here, the severe constraints imposed by the four-membered ring force the HB donor and acceptor to be far apart and the IMHB is rather weak. These geometrical constraints are less severe for the saturated analogues and the IMHB becomes stronger, confirming that the characteristics of the sigma-skeleton, and not the resonance-assisted hydrogen bond (RAHB) phenomenon, are the primary contributors to the strength of the IMHB in conjugated compounds.
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Affiliation(s)
- Pablo Sanz
- Departamento de Química, C-9, Universidad Autónoma de Madrid, Cantoblanco, 28049, Madrid, Spain
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Huang L, Huang Y, Chi Y, Lin J, Yu L, Xu L, Chen G. Study on the kinetics of keto-enol tautomerism of p-hydroxyphenylpyruvic acid using capillary electrophoresis. J Chromatogr A 2007; 1175:283-8. [PMID: 18021791 DOI: 10.1016/j.chroma.2007.10.078] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2007] [Revised: 10/18/2007] [Accepted: 10/19/2007] [Indexed: 11/24/2022]
Abstract
The kinetics of keto-enol tautomerism of p-hydroxyphenylpyruvic acid (pHPP) as a model of alpha-carbonyl compounds in aqueous solution at room temperature (25 degrees C) was first investigated by capillary electrophoresis with UV detection at 200 nm. The two tautomers could be separated and detected within 3 min. Since the ketonization of enolic pHPP varied with the buffer composition and buffer pH, the kinetics of pHPP was studied under different conditions, and relevant distributing fractions of enolic pHPP, ketonization rate constants and half-life were determined. In addition, beta-CD played an important part in the separation of the two tautomers, thus, the interaction between pHPP and beta-CD was also investigated by electrochemical techniques.
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Affiliation(s)
- Lu Huang
- Ministry of Education Key Laboratory of Analysis and Detection Technology for Food Safety (Fuzhou University), Fuzhou, Fujian 350002, China
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Ośmiałowski B, Raczyńska ED, Krygowski TM. Tautomeric equilibria and pi electron delocalization for some monohydroxyarenes--quantum chemical studies. J Org Chem 2007; 71:3727-36. [PMID: 16674042 DOI: 10.1021/jo052615q] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Keto-enol tautomeric interconversions and variations of the pi-electron distribution were studied for 11 isolated monohydroxyarenes at the DFT(B3LYP)/6-311++G(2df,2p) level. For two monohydroxyarenes (phenol and 9-anthrol), the PCM model of solvation (water) was also applied to the DFT geometries. The geometry-based HOMA index was applied to estimate pi-electron delocalization in the keto and enol tautomeric forms. Thermodynamic parameters of tautomeric interconversions (DeltaET, DeltaGT, TDeltaST, pKT) were calculated to estimate relative stabilities of individual tautomers and their percentage contents in the tautomeric mixtures. In almost all cases, the aromatic enol forms are strongly favored. An exception is 9-anthrol, which prefers its keto form. The resonance stabilization of this form comes from the central ring. Generally, aromaticity is the main factor that influences tautomeric equilibria in monohydroxyarenes. Hydration effect is considerably smaller and it does not change the tautomeric preference.
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Affiliation(s)
- Borys Ośmiałowski
- Department of Chemistry, Technical and Agricultural University, ul. Seminaryjna 3, 85-326 Bydgoszcz, Poland
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28
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Novel tocopheryl compounds XXIV. Studies into the nitrosation chemistry of γ-tocopherol: preparation of 5-nitroso-γ-tocopherol via an organomercury derivative of vitamin E. Tetrahedron 2007. [DOI: 10.1016/j.tet.2007.02.120] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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29
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Sanz P, Mó O, Yañez M, Elguero J. Resonance-assisted hydrogen bonds: a critical examination. Structure and stability of the enols of beta-diketones and beta-enaminones. J Phys Chem A 2007; 111:3585-91. [PMID: 17429952 DOI: 10.1021/jp067514q] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The characteristics of the intramolecular hydrogen bond (IMHB) for a series of 40 different enols of beta-diketones and their nitrogen counterparts have been systematically analyzed at the B3LYP/6-311+G(3df,2p)//B3LYP/6-311+G(d,p) level of theory. In some cases, two tautomers may exist which are interconnected by a hydrogen shift through the IMHB. In tautomer a the HB donor group (YH) is attached to the six-membered ring, while in tautomer b the HB acceptor (X) is the one that is attached to the six-membered ring. We found that changing an O to a N favors the a tautomer when the atom is endo and the contrary when it is exo, while the presence of a double bond favors the a tautomers. As expected, the OH group behaves as a better HB donor than the NH2 group and the C=NH group as a better HB acceptor than the C=O group, although the first effect clearly dominates. Accordingly, the expected IMHB strength follows the [donor, acceptor] trend: [OH, C=NH] > [OH, C=O] > [NH2, C=NH] > [NH2, C=O]. For all those compounds in which the functionality exhibiting the IMHB is unsaturated (I-type), the IMHB is much stronger than in their saturated counterparts (II-type). However, when the systems of the II-type subset, which are saturated, are constrained to have the HB donor and the HB acceptor lying in the same plane and at the same distance as in the corresponding unsaturated analogue, the IMHB is of similar or even larger strength. Hence, we conclude that, at least for this series of unsaturated compounds, the resonance-assisted hydrogen bond effect is not the primary reason behind the strength of their IMHBs, which is simply a consequence of the structure of the sigma-skeleton of the system that keeps the HB donor and the HB acceptor coplanar and closer to each other.
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Affiliation(s)
- Pablo Sanz
- Departamento de Química, C-9, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
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Sobczyk L, Grabowski SJ, Krygowski TM. Interrelation between H-bond and Pi-electron delocalization. Chem Rev 2005; 105:3513-60. [PMID: 16218560 DOI: 10.1021/cr030083c] [Citation(s) in RCA: 522] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Lucjan Sobczyk
- Faculty of Chemistry, University of Wrocław, Joliot-Curie 14, 50 383 Wrocław, Poland
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Raczyńska ED, Kosińska W, Ośmiałowski B, Gawinecki R. Tautomeric Equilibria in Relation to Pi-Electron Delocalization. Chem Rev 2005; 105:3561-612. [PMID: 16218561 DOI: 10.1021/cr030087h] [Citation(s) in RCA: 247] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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