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Mesomeric Betaine (mesomeric + betaine)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Nucleophilic Carbenes and Pseudo-Cross-Conjugated Mesomeric Betaines of Indazole Starting from Analogues of the Alkaloid-Betaine Nigellicine

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2005
Andreas Schmidt
Abstract The alkaloid Nigellicine possesses the indazolium-3-carboxylate ring system as electronically relevant partial structure which represents a member of the class of pseudo-cross-conjugated mesomeric betaines. Indazolium-3-carboxylate, prepared starting from indazole-3-carboxylic acid by an esterification,methylation,saponification sequence, can be converted into the isoconjugated phenyl- and 4-(nitrophenyl)amidates and the thiocarboxylate as additional examples of pseudo-cross-conjugated systems. In accordance with results of ab initio calculations decarboxylation of indazolium-3-carboxylate with formation of the nucleophilic carbene indazol-3-ylidene begins at approximately 40 °C as evidenced by temperature-dependent NMR spectroscopy. The carbene can be trapped with protons as indazolium salts, and carbon dioxide which reconstitutes the pseudo-cross-conjugated mesomeric betaine. According to the calculations, the carbene adopts a singlet ground state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Vibrational spectra and quantum chemical calculations of uracilyl,pyridinium mesomeric betaine

JOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2007
A. Schmidt
Abstract Modified nucleobases (MNs) are promising molecules with potential application in non-linear optic (NLO) and drug design against a wide number of diseases. In the present paper we report studies on a cross-conjugated mesomeric betaine, which can act as a MN, formed by the covalent union of a 4-dimethylamino pyridinium and a uracilyl groups. The molecule thus formed must be presented by a dipolar canonical formulae in which positive and negative charges are delocalized within separated moieties. Quantum chemistry density functional theory (DFT) calculations, at the B3PW91/6-31G** level, and Fourier transform (FT) infrared and Raman spectra of this molecule and its N -deuterated derivative were performed. The calculated structural properties over the ground state optimized structure evidenced a strong separation between the two conjugated systems. Comparison with previous results obtained for the cationic species indicated that N -protonation clearly affects the degree of conjugation. Assignments of the FT-IR and FT-Raman spectra were supported by the DFT wavenumbers, intensities and normal modes, which also evidenced the separation of the two conjugated systems. Significant deviations were found for the stretching force constants of the inter-ring and the uracilyl skeletal bonds when comparing this molecule with its N -protonated species. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Nucleophilic Carbenes and Pseudo-Cross-Conjugated Mesomeric Betaines of Indazole Starting from Analogues of the Alkaloid-Betaine Nigellicine

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2005
Andreas Schmidt
Abstract The alkaloid Nigellicine possesses the indazolium-3-carboxylate ring system as electronically relevant partial structure which represents a member of the class of pseudo-cross-conjugated mesomeric betaines. Indazolium-3-carboxylate, prepared starting from indazole-3-carboxylic acid by an esterification,methylation,saponification sequence, can be converted into the isoconjugated phenyl- and 4-(nitrophenyl)amidates and the thiocarboxylate as additional examples of pseudo-cross-conjugated systems. In accordance with results of ab initio calculations decarboxylation of indazolium-3-carboxylate with formation of the nucleophilic carbene indazol-3-ylidene begins at approximately 40 °C as evidenced by temperature-dependent NMR spectroscopy. The carbene can be trapped with protons as indazolium salts, and carbon dioxide which reconstitutes the pseudo-cross-conjugated mesomeric betaine. According to the calculations, the carbene adopts a singlet ground state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Electrospray ionization mass spectrometric studies of nucleophilic carbenes derived from pyrazolium and indazolium carboxylates

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2005
Andreas Schmidt
Pyrazolium-3-carboxylate and indazolium-3-carboxylate, which belong to the class of pseudo-cross-conjugated mesomeric betaines and which represent the electronically relevant partial structures of the betaine alkaloid Nigellicin, were examined by electrospray ionization mass spectrometry. These compounds decarboxylate to pyrazol-3-ylidene and indazol-3-ylidene. The formation of adducts of these new nucleophilic carbenes under the measurement conditions was examined. Copyright © 2005 John Wiley & Sons, Ltd. [source]