Conformational and tautomeric eccentricities of 2-acetyl-1,8-dihydroxynaphthalenes

Poul Erik Hansen; Fadhil S. Kamounah; Bjarke Knud Vilster Hansen; Jens Spanget-Larsen

Conformational and tautomeric eccentricities of 2-acetyl-1,8-dihydroxynaphthalenes

Poul Erik Hansen, Fadhil S. Kamounah, Bjarke Knud Vilster Hansen, Jens Spanget-Larsen

Kemi

Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › peer review

Abstract

Udgivelsesdato: Februar

Originalsprog	Engelsk
Tidsskrift	Magnetic Resonance in Chemistry
Vol/bind	45
Udgave nummer	2
Sider (fra-til)	106-117
Antal sider	12
ISSN	0749-1581
Status	Udgivet - 2007

Citer dette

@article{879d3fb09f1911db9f01000ea68e967b,

title = "Conformational and tautomeric eccentricities of 2-acetyl-1,8-dihydroxynaphthalenes",

abstract = "Tautomerism in aromatic systems with oxygen substiuents is rare. This is investigated in 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (1) and in 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (2). The tautomeric nature of 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene is supported by long-range hydrogen-hydrogen coupling between the OH-1 and the OH-8 and by the isotope effects on 13C caused by deuteration at the CH3C=O methyl group. Compound 2 participates in a degenerate equilibrium between two equivalent nonsymmetrical rotamers (2A and 2B) , each having two intramolecular O...HO hydrogen bonds: one involving an acetyl oxygen and the neighbouring hydroxyl group, and the other between the oxygen centers at positions 1 and 8. In addition, each rotamer is involved in a tautomeric equilibrium, with a structure having an OH-substituted exocyclic double bond (2AT or 2BT). - DFT calculations for a large set of compounds highlight the factors controlling the unusual rotational and tautomeric behaviors. A very important factor seems to be the repulsive interaction between the O-1 and O-8 centers, which is modulated by formation of an OH-1...O-8 or OH-8..O-1 hydrogen bond. Steric interactions, mesomeric release of electrons from the oxygen at position 8, and a strong OH...O=C hydrogen bond are other factors. - Solid-state 13C NMR spectra of 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene at different temperatures demonstrated no averaging in the solid, whereas partially deuterated 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene showed an isotope effect at C-1 of 1.5 ppm, indicating tautomerism in the solid state.",

keywords = "2-acetyl-1,8-dihydroxynaphthalenes, tautomerism, intramolecular hydrogen bonding, isotope effects, chemical shifts, OH,OH spin-spin coupling, solid-state NMR",

author = "Hansen, {Poul Erik} and Kamounah, {Fadhil S.} and Hansen, {Bjarke Knud Vilster} and Jens Spanget-Larsen",

year = "2007",

language = "English",

volume = "45",

pages = "106--117",

journal = "Magnetic Resonance in Chemistry",

issn = "0749-1581",

publisher = "JohnWiley & Sons Ltd.",

number = "2",

}

TY - JOUR

T1 - Conformational and tautomeric eccentricities of 2-acetyl-1,8-dihydroxynaphthalenes

AU - Hansen, Poul Erik

AU - Kamounah, Fadhil S.

AU - Hansen, Bjarke Knud Vilster

AU - Spanget-Larsen, Jens

PY - 2007

Y1 - 2007

N2 - Tautomerism in aromatic systems with oxygen substiuents is rare. This is investigated in 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (1) and in 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (2). The tautomeric nature of 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene is supported by long-range hydrogen-hydrogen coupling between the OH-1 and the OH-8 and by the isotope effects on 13C caused by deuteration at the CH3C=O methyl group. Compound 2 participates in a degenerate equilibrium between two equivalent nonsymmetrical rotamers (2A and 2B) , each having two intramolecular O...HO hydrogen bonds: one involving an acetyl oxygen and the neighbouring hydroxyl group, and the other between the oxygen centers at positions 1 and 8. In addition, each rotamer is involved in a tautomeric equilibrium, with a structure having an OH-substituted exocyclic double bond (2AT or 2BT). - DFT calculations for a large set of compounds highlight the factors controlling the unusual rotational and tautomeric behaviors. A very important factor seems to be the repulsive interaction between the O-1 and O-8 centers, which is modulated by formation of an OH-1...O-8 or OH-8..O-1 hydrogen bond. Steric interactions, mesomeric release of electrons from the oxygen at position 8, and a strong OH...O=C hydrogen bond are other factors. - Solid-state 13C NMR spectra of 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene at different temperatures demonstrated no averaging in the solid, whereas partially deuterated 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene showed an isotope effect at C-1 of 1.5 ppm, indicating tautomerism in the solid state.

AB - Tautomerism in aromatic systems with oxygen substiuents is rare. This is investigated in 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (1) and in 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (2). The tautomeric nature of 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene is supported by long-range hydrogen-hydrogen coupling between the OH-1 and the OH-8 and by the isotope effects on 13C caused by deuteration at the CH3C=O methyl group. Compound 2 participates in a degenerate equilibrium between two equivalent nonsymmetrical rotamers (2A and 2B) , each having two intramolecular O...HO hydrogen bonds: one involving an acetyl oxygen and the neighbouring hydroxyl group, and the other between the oxygen centers at positions 1 and 8. In addition, each rotamer is involved in a tautomeric equilibrium, with a structure having an OH-substituted exocyclic double bond (2AT or 2BT). - DFT calculations for a large set of compounds highlight the factors controlling the unusual rotational and tautomeric behaviors. A very important factor seems to be the repulsive interaction between the O-1 and O-8 centers, which is modulated by formation of an OH-1...O-8 or OH-8..O-1 hydrogen bond. Steric interactions, mesomeric release of electrons from the oxygen at position 8, and a strong OH...O=C hydrogen bond are other factors. - Solid-state 13C NMR spectra of 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene at different temperatures demonstrated no averaging in the solid, whereas partially deuterated 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene showed an isotope effect at C-1 of 1.5 ppm, indicating tautomerism in the solid state.

KW - 2-acetyl-1,8-dihydroxynaphthalenes

KW - tautomerism

KW - intramolecular hydrogen bonding

KW - isotope effects

KW - chemical shifts

KW - OH,OH spin-spin coupling

KW - solid-state NMR

M3 - Journal article

SN - 0749-1581

VL - 45

SP - 106

EP - 117

JO - Magnetic Resonance in Chemistry

JF - Magnetic Resonance in Chemistry

IS - 2

ER -