<sup>13</sup>C‐NMR. Spectra of Pteridines

Muller, Georges; Philipsborn, W. Von

doi:10.1002/hlca.19730560751

Cited by 43 publications

(6 citation statements)

References 11 publications

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“…According to the nonsymmetric substitution pattern of the central pyrimidine, the 13 C NMR spectra of all compounds showed four quaternary carbon atoms of the pyrimidine moiety. In general, the C-5 resonances of 4(3 H )-pyrimidones are not significantly influenced in passing from the neutral to the anionic species . Likewise, the chemical shifts of the C-5 positions of the dications and the betaines are similar, whereas the resonances of the C-2 and C-6 atoms differ significantly [e.g., 11 : δ = 152.21, 152.77 ppm; 8a : δ = 150.82, 155.49 ppm].…”

Section: Resultsmentioning

confidence: 99%

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Heteroaromatic Tripoles. 2,6-Bis(hetarenio)pyrimidin-4-olates: Hybrids between Hetarenium Salts and Cross-Conjugated Mesomeric Betaines

Schmidt

Kindermann

1998

J. Org. Chem.

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A novel tandem nucleophilic displacement reaction on tetrachloropyrimidine 7 leads to molecules with two delocalized positive and one delocalized negative charge, which comprise a common π-electron system, plus one external anion. Thus, treatment of 7 with an excess of heteroaromatic nucleophiles such as 4-(dimethylamino)pyridine, 4-(pyrrolidin-1-yl)pyridine, and 1-methylimidazole, respectively, followed by the addition of water formed the tripolar bis(hetarenio)pyrimidin-4-olates 8, 9, and 10. Addition of anhydrous alcohols furnished the O-alkylated dicationic species 11-16. We contrast the spectroscopic features of the monocationic 8-10 and the dicationic 11-16 and performed a conformational study (PM3). The HOMO/LUMO profile was calculated to evaluate our classification of 8-10 as CCMB derivatives.

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Section: Resultsmentioning

confidence: 99%

“…In continuation of our work on charge-cumulated and charge-separated pyrimidines, we chose the pyrimidin-4-olate moiety I , the anion of 4( 3H )-pyrimidone, as the target fragment of the desired heterocyclic tripoles. The delocalized negative charge is associated with a fragment that is isoconjugate with the benzyl anion II .…”

Section: Resultsmentioning

confidence: 99%

Heteroaromatic Tripoles. 2,6-Bis(hetarenio)pyrimidin-4-olates: Hybrids between Hetarenium Salts and Cross-Conjugated Mesomeric Betaines

Schmidt

Kindermann

1998

J. Org. Chem.

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“…We have previously observed that an alkyl group at position 6 activates the reactive methyl group at the neighbouring positions in 1 and 5, whereas more distant methyl groups are substantially deactivating, as shown, for example, by the mutua1 deactivating effects of the 5-and 7-methyl groups in 5 (R = R' = CH,) (6,7).…”

Section: Introductionmentioning

confidence: 95%

“…Although the general base catalyzed reaction is thus disqualified from consideration in this respect, the general acid catalyzed reaction is not. This is because protonation occurs at N-8 in 2 (7), and at N-1 in 1,' which produces identical cations except for the substitution of hydrogen for methyl at N-8 (eqs.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, base strength, and prototropic behaviour of a number of alkyllumazines

Stewart¹,

Gumbley²

1985

Can. J. Chem.

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A number of lumazines and 5-deazalumazines containing a methyl group at C-7 have been prepared, their pKBH+ values determined, and measurements made of the rates at which the hydrogen atoms of their 7-methyl groups undergo isotopic exchange in aqueous sulfuric acid. The presence of an alkyl group at N-8 in the protonated forms of these compounds activates the neighbouring methyl group at C-7; the effect is considerably larger than that previously observed for a methyl group at C-6, which is the other neighbouring position. The comparison of methyl and hydrogen at N-8 can be made only for the acid-catalyzed reaction because the structures of the neutral compounds, which take part in the base-catalyzed reaction, are not analogous.Ross STEWART et S. J. GUMBLEY. Can. J. Chem. 63, 3290 (1985) On a prkpark un certain nombre de lumazines et de dCaza-5 lumazines contenant un groupement mkthyle en position C-7; de plus, on a determink les valeurs de leurs pKBH+ et, opkrant dans de I'acide sulfurique aqueux, on a mesure les vitesses d'kchange isotopique des atomes d'hydrogenes de leurs groupements mkthyles en C-7. La prksence d'un groupement alkyle dans la position N-8 des formes protonkes de ces composCs active le groupement mCthyle voisin en C-7; cet effet est beaucoup plus important que celui observk antkrieurement pour un groupement mCthyle en C-6, I'autre position adjacente. On ne peut faire une cornparaison entre les effets des groupements mkthyles et ceux des atomes d'hydrogenes en N-8 que pour les rkactions acido-catalysCes puisque les structures des composks neutres, qui prennent part 3 la rkaction catalyske par les bases, ne sont pas semblables.[Traduit par le journal]

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“…*H Chemical Shifts0 of Nicotinic Acid and Its Charged Species (C = 0.148 M) 20:80 (v/v)5 values in ppm from DSS as internal reference.…”

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confidence: 99%

Hydrogen-1 and carbon-13 nuclear magnetic resonance investigation of nicotinic acid, its anion, and cation, in water and water-dimethyl sulfoxide mixtures. Influence of dimethyl sulfoxide on relative acidities

Khan¹,

Hallé²,

Simonnin³

et al. 1977

J. Phys. Chem.

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Publication costs assisted by the University Pierre et Marie Curie !H and 13C NMR spectra of nicotinic acid, its anion, and cation have been studied in water and in the 20:80 (v/v) H20/Me2S0 mixture (concentration 0.148 M). Characteristic protonation shifts for N protonation and COO" protonation allow an unambiguous determination of the protonation site and reveal an inversion of relative acidities on going from water to H20/Me2S0 mixture. Experimental results indicate that the tautomeric equilibrium between neutral forms of nicotinic acid is displaced toward the zwitterionic form in water, but toward the molecular form in Me2SO. pKa values calculated from 13C titration curves obtained at 20 °C are in excellent agreement with those obtained by a potentiometric study.

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¹³C‐NMR. Spectra of Pteridines

Cited by 43 publications

References 11 publications

Heteroaromatic Tripoles. 2,6-Bis(hetarenio)pyrimidin-4-olates: Hybrids between Hetarenium Salts and Cross-Conjugated Mesomeric Betaines

Heteroaromatic Tripoles. 2,6-Bis(hetarenio)pyrimidin-4-olates: Hybrids between Hetarenium Salts and Cross-Conjugated Mesomeric Betaines

Synthesis, base strength, and prototropic behaviour of a number of alkyllumazines

Hydrogen-1 and carbon-13 nuclear magnetic resonance investigation of nicotinic acid, its anion, and cation, in water and water-dimethyl sulfoxide mixtures. Influence of dimethyl sulfoxide on relative acidities

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13C‐NMR. Spectra of Pteridines

Cited by 43 publications

References 11 publications

Heteroaromatic Tripoles. 2,6-Bis(hetarenio)pyrimidin-4-olates: Hybrids between Hetarenium Salts and Cross-Conjugated Mesomeric Betaines

Heteroaromatic Tripoles. 2,6-Bis(hetarenio)pyrimidin-4-olates: Hybrids between Hetarenium Salts and Cross-Conjugated Mesomeric Betaines

Synthesis, base strength, and prototropic behaviour of a number of alkyllumazines

Hydrogen-1 and carbon-13 nuclear magnetic resonance investigation of nicotinic acid, its anion, and cation, in water and water-dimethyl sulfoxide mixtures. Influence of dimethyl sulfoxide on relative acidities

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¹³C‐NMR. Spectra of Pteridines