Symmetry and tunneling in the intramolecular proton exchange in naphthazarin, methylnaphthazarin, and dimethylnaphthazarins

Vega, J. R. De La; Busch, J. H.; Schauble, J. Herman; Kunze, Kathryn L.; Haggert, Brian E.

doi:10.1021/ja00376a007

Cited by 75 publications

(18 citation statements)

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“…lc) is found 47 kJ/mol higher in energy relatively to the lowest energy minimum and is characterized as a local minimum. Such a result suggests the existence of two stable isomers of naphthazarin having C2v and C2h symmetry, and this conclusion is in contrast with the previous STO-3G investigation, which predicted the C2~ configuration as the unique stable structure [10].…”

Section: Energies and Intramoleeular Proton Transfercontrasting

confidence: 93%

“…The geometries of each structure were fully optimized by using the 6-31G basis set, and vibrational frequencies were computed to characterize each stationary point as true minima or higher-order saddle points on the potential energy surface and to determine the zero-point corrections to the total energies (ZPE) of the stable structures. In agreement with previous AM1 [1] and HF/STO-3G [10] theoretical calculations, the most stable isomer of naphthazarin has C2v symmetry ( Fig. la).…”

Section: Energies and Intramoleeular Proton Transfersupporting

confidence: 91%

“…lc) rather than a one-step mechanism involving the simultaneous transfer of both the protons through the centrosymmetric species D2h (Fig. If), as indicated by HF/STO-3G calculations [10].…”

Section: Energies and Intramoleeular Proton Transfermentioning

confidence: 91%

“…lc and lf) to be ruled out as alternative structures for the isolated molecule. The theoretical study of the structure and intramolecular hydrogen bonding of the naphthazarin molecule has been addressed in the past with semiempirical methods [1] and minimal basis set ab initio calculations [10], and has allowed an evaluation of the structural and energetic features of the gas-phase molecule. Quite recently, the dynamic of the intramolecular proton exchange has been attacked with MINDO/3 semiempirical methods, and the symmetry group of labile intramoleculafly hydrogen bonded naphthazarin has been deduced as Cs(M) [11].…”

Section: Introductionmentioning

confidence: 99%

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Ab initio HF-SCF study of naphthazarin: Geometries, isomerism, hydrogen bonding, and vibrational spectrum

Ramondo¹,

Bencivenni²

1994

Struct Chem

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The structural properties and intmmolecular hydrogen bonding of a series of structures of naphthazarin molecule were investigated by ab initio HF-SCF methods. The geometries of the C2~,, C2h, D2h, and Cs symmetry structures were optimized using split-valence basis sets. MP2/6-31G*// HF/6-31G single-point energy calculations indicate that the C2,, isomer (5,8-dihydroxy-l,4-naphthoquinone) is the lowest energy structure of the molecule and that the C2h symmetry one (4,8-dihydroxy-l,5-naphthoquinone), lying 37 kJ/mol above the C2,, form, is the other stable isomer of naphthazarin. At the HF/6-31G level, the intramolecular proton exchange between two equivalent C2v structures is a two-step process where each proton can be independently transferred through an unsymmetrical potential having a 1,5-quinone intermediate, the C2h symmetry structure, and two equivalent transition states of Cs symmetry, with a barrier height equal to 38 kJ/ tool (MP2/6-31G*//HF/6-31G). The study of naphthazarin molecule is flanked by a theoretical investigation on the C2v and C2h isomers of the parent naphthoquinone and dihydroxynaphthalene molecules. The SCF vibrational spectrum of the ground state of naphthazarin, harmonic frequencies, and infrared and Raman band intensities were computed at the HF/6-3 IG level. The results of the calculations are compared with the matrix isolation FT-IR spectroscopy measurements and with the infrared and Raman spectra of the crystal molecule.KEY WORDS: Naphthazarin; intramolecular hydrogen bonding; internal proton exchange; ab initio calculations, vibrational spectrum.

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Section: Energies and Intramoleeular Proton Transfercontrasting

confidence: 93%

Section: Energies and Intramoleeular Proton Transfersupporting

confidence: 91%

Section: Energies and Intramoleeular Proton Transfermentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Ab initio HF-SCF study of naphthazarin: Geometries, isomerism, hydrogen bonding, and vibrational spectrum

Ramondo¹,

Bencivenni²

1994

Struct Chem

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“…In 1982, de La Vega et al 37 reported the first computational study of tautomerism in naphthazarin (1) and methyl derivatives by ab initio calculations applying a minimum basis set. The authors concluded that 1a and 1b are global energetic minima while 1c and 1d are saddle points 104.6 kJ mol - 43 reported a CAM-B3LYP/6-31G** study of naphthazarin tautomerism in order to investigate its electronic structure.…”

Section: Introductionmentioning

confidence: 99%

Computational Study of Electronic Effects from β-Substituents on the Tautomerism of Naphthazarin Derivatives

Grasel

Castanho

Fontoura

et al. 2016

Journal of the Brazilian Chemical Society

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In this work, semi-empirical AM1 and DFT B3LYP/6-31G** calculations were applied in the study of the interconversion among tautomers of several naphthazarin and 5-amino-8-hydroxy-1,4-naphthoquinone β-substituted derivatives bearing electron-donor or electron-withdrawing groups. Using a semi-empirical method, detailed potential energy landscapes for proton transfers were built, from which four tautomers and four transition states of interconversions were identified for each compound. These structures were recalculated without restraints and, using the Boltzmann distribution, the populations for each of the four tautomers and their respective molar fractions were calculated. The calculations showed that the tautomeric equilibrium is shifted to the tautomer where the ring with the substituent has a quinonic nature and is more pronounced when the β-substituent is an electron donor group. For derivatives of 5-amino-8-hydroxy-1,4-naphthoquinone, an equilibrium between an aromatic and a 1,5-naphthoquinonic non-aromatic enamine was observed, being the former the most stable.Keywords: tautomerism, B3LYP, AM1, molecular modeling, electronic effect IntroductionNaphthoquinones belong to a large class of natural and synthetic compounds. These compounds are frequently found in plants and on a smaller scale in inferior animals, exhibiting a broad scope of applications, such as drugs and dyes.1-9 5,8-Dihydroxy-1,4-naphthoquinone (1), naphthazarin, and its derivatives are particularly important due to their biological and pharmacological activities [10][11][12][13][14][15] and versatility as intermediates in the synthesis of more diversified chemical structures. 9,[16][17][18][19][20][21][22][23][24] One of their features is the presence of tautomerism. 12,25The tautomeric equilibrium changes their reactivity and spectroscopic properties. 16,18,20 Therefore, a systematic investigation of dihydroxy-1,4-naphthoquinones tautomerism can contribute to the understanding of their chemical reactivity, pharmacological activity, and spectroscopic characteristics. Despite being a quite simple concept, tautomerism is a phenomenon that still arises interest and has been the aim of several recent studies due to its great importance to organic and medicinal chemistry, biochemistry, pharmacology and molecular biology. 26 In many cases, the biological activity of a molecule or its reaction mechanism with biological receptors is strongly dependent on the tautomerism. However, experimental studies involving tautomerism are very difficult due to the fast reaction rate of these processes. Naphthazarin (1) and its derivatives are able of hydrogen transfer from the hydroxyl to the syn periplanar carbonyl groups. For each derivative, four tautomers can be drawn (Scheme 1). 27Glazunov and Berdyshev 28 studied the effect from mono to tetrachloro substitution on naphthazarin using DFT B3LYP/6-31G**. Their results showed that the strength of the intramolecular H-bond increases when the chlorine β-substitution is near to hydroxyl groups, but decreases in th...

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1994

Advances in Chemical Physics

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Symmetry and tunneling in the intramolecular proton exchange in naphthazarin, methylnaphthazarin, and dimethylnaphthazarins

Cited by 75 publications

References 0 publications

Ab initio HF-SCF study of naphthazarin: Geometries, isomerism, hydrogen bonding, and vibrational spectrum

Ab initio HF-SCF study of naphthazarin: Geometries, isomerism, hydrogen bonding, and vibrational spectrum

Computational Study of Electronic Effects from β-Substituents on the Tautomerism of Naphthazarin Derivatives

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