Search results for "Spectroscopy"

1988

Hydrolysis of Phytic Acid by Microwave Treatment: Application to Phytic Acid Analysis in Pharmaceutical Preparations

1998

Abstract The acid hydrolysis of phytic acid in a Teflon reactor using a domestic microwave oven has been studied and compared with other reported procedures. In 0.44 M HCl quantitative hydrolysis was achieved with six heating stages of 2 min each. A lower yield was obtained with H 2 SO 4 and HNO 3 . The analytical use of this hydrolysis to determine phytic acid by indirect determination of phosphate has been demonstrated by analysis of three pharmaceutical formulations. No sample pretreatment other than obtaining a homogeneous suspension was necessary.

New Sesquiterpene Lactones and Other Constituents fromCentaurea paui

1997

Aerial parts of Centaurea paui afforded, in addition to several known sesquiterpene lactones, the two new elemanolides 2–4, the new elemane derivative 5 as well as the five new heliangolides 14–18. Their structures were elucidated by spectroscopic methods, especially high-field NMR spectroscopy. The structure of the heliangolide 12 previously isolated from this plant, has been confirmed by X-ray diffraction.

The effect of chlorine substituent(s) on the primary loss of a methyl radical from chlorinated veratroles (1,2-dimethoxybenzenes)

1989

Trichomonazide Wirkstoffe, 2. Mitt. Verzweigtkettig 4,6-disubstituierte 2-Cyanaminopyrimidine

1985

Aus der Umsetzung von Dicyandiamid (1) mit den β-Diketonen 2a–b gehen die 4,6-verzweigtkettig disubstituierten 2-Cyanaminopyrimidine 3a–b hervor. Fur Strukturtyp 3 last sich aus den spektroskopischen Daten, speziell aus den 1H- und 13C-NMR-Werten, das Vorliegen eines Gleichgewichts zwischen den tautomeren 2-Cyanamino- und 2-Cyaniminopyrimidinformen ableiten. 3 zeichnet sich durch trichomonazide, antivirale und antimykotische Wirkung aus. Trichomonacidal Agents, II: 4,6-Disubstituted 2-(Cyanoamino)pyrimidines Carrying Branched Substituents The reaction of dicyandiamide (1) with the β-diketones 2a–b yields the 4,6-branched disubstituted 2-(cyanoamino)pyrimidines 3a–b. From spectroscopic evide…

ChemInform Abstract: Synthesis of Pyrido(2,3-d)pyrimidines in the Reaction of 6-Amino-2,3- dihydro-2-thioxo-4(1H)-pyrimidinone with Chalcones.

2010

6-Amino-2,3-dihydro-2-thioxo-4(1H)-pyrimidinone (1) reacts in boiling DMF with α,/β-unsaturated ketones 2 yielding the pyrido[2,3-d]pyrimidine systems 5 and 6, respectively. The orientation in the addition process can be determined by nmr measurements, especially by NOE difference spectroscopy. The products do not correspond to a normal Skraup or Doebner-v. Miller synthesis.

Theoretical characterization of the absorption spectra of phenanthrene and its radical cation

2003

The vertical absorption spectra of phenanthrene and its radical cation have been studied theoretically by means of a multiconfigurational second-order perturbation approach. Singlet-singlet transition energies and oscillator strengths, and singlet-triplet excitation energies have been studied in the absorption spectrum of phenanthrene up to 6 eV. The absorption spectrum of the pehnanthrene radical cation has been computed up to 3.4 eV. The results obtained confirm previous assignments and also lead to new interpretations of the main features of the spectra of these systems.

Stereocontrolledα-Alkylation of Fully ProtectedL-Serine

2004

Diastereoselective alkylation of the (2S,4S) and (2R,4S) diastereomers of 3-tert-butyl 4-methyl 2-tert-butyl-1,3-oxazolidine-3,4-dicarboxylate (1a/b) is reported. Formation of both diastereomers of these oxazolidines was achieved by changing the order of protection steps, and their relative and absolute configurations were determined by NOESY spectroscopy. The use of the bulky ring substituent tBu together with Boc as the N-protecting group led to the exclusive formation of only one alkylated diastereomer. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Benzodiselenagermoles and spirobisbenzodiselenagermoles

1993

Synthesis of benzodiselenagermoles and bisbenzodiselenagermoles was carried out by transmetallation group 4 group 14 between diselenophenylenezirconocenes and dialkyl-, diaryl- or alkylaryldichlorogermanes, aryltrichlorogermane or germanium tetrachloride. The new compounds were studied by 1H, 77Se NMR and mass spectrometry. In the case of compounds with substituted phenyl groups, double irradiation and 2D NMR experiments were performed to determine the chemical shifts of the two selenium atoms. The crystal structure of a spirobisbenzodiselenagermole has been established by X-ray diffraction analysis.

A Bichromophore Based on Perylene and Terrylene for Energy Transfer Studies at the Single-Molecule Level

1999

A functionalized dialkylperylene and a modified terrylenetetracarboxdiimide (TTCDI) were joined by a hexanediyl spacer. The resulting bichromophoric molecule 1 (R = 4-tert-butylphenoxy) is a suitable model system for donor–acceptor energy transfer studies at the single-molecule level.