Search results for "double bond"
showing 10 items of 184 documents
Molecular structures and vibrations of m-methylaniline in the S0 and S1 states studied by laser induced fluorescence spectroscopy and ab initio calcu…
2000
Abstract The UV fluorescence excitation and dispersed fluorescence spectra of a jet-cooled m-methylaniline have been obtained for the S1←S0 transition, in which some of the bands have been observed for the first time. The main spectral bands have been assigned by comparison with those of other relevant substituted benzenes. It was found that the spectra exhibit an important feature which is the internal rotation of the methyl group in the electronic ground and excited states. Ab initio calculations at MP2/6-31G* and CIS/6-31G* show that the optimized structure of m-methylaniline in the ground state is not planar with the amino group having sp3 hybridation-like character due to the existence…
[39] Lipoperoxyl radical-scavenging activity of vitamin A and analogs in homogeneous solution
1994
Publisher Summary This chapter describes the assay method for determining the reactivity of all- trans -retinol and other natural and synthetic retinoids, with radicals generated by reaction of the lipid-soluble azo initiator 2,2 ' -azobis(2,4-dimethylvaleronitrile) (AMVN) with methyl linoleate. The chapter discusses the general principles for measuring antioxidant activity. The oxidation of linoleic acid methyl ester (LAME) is the simplest model for studying the oxidation of polyunsaturated lipids and has been widely adopted to evaluate antioxidant activity. Because linoleic acid has two double bonds, peroxidation occurs at the bisallylic hydrogens and generates conjugated diene hydroperox…
Molecular Recognition-Induced Function and Competitive Replacement by Hydrogen-Bonding Interactions: Amphiphilic Barbituric Acid Derivatives, 2,4,6-…
1998
The phenomenon of molecular recognition inducing further function is common in nature. However, there are few synthetic systems which achieve this cascade type mechanism, and those are generally ca...
Cycloaddition reactions of benzothiete and hetero dienophiles for the synthesis of heterocyclic systems
1986
Abstract Benzothiete ( 1 ) undergoes cycloaddition reactions with hetero dienophiles with NN-, NO- or CO- double bonds, leading to six-membered heterocyclic ring systems of 2H-3,4-dihydro-1,2,3-benzothiadiazine ( 3 ), 4H-3,1,2-benzoxathiazine ( 4 ) and 4H-3,1-benzoxathiin.
Geometric and electronic structure of dithiapyranylidine: evolution upon oxidation
1993
Abstract We present a theoretical investigation of the modifications that successive oxidation induces on the geometric and electronic structures of the π-electron donor dithiapyranylidene. The lengthening of the double bonds and the shortening of the single bonds calculated as the molecular charge increases indicate a gain of aromaticity with oxidation. Both the geometricand the electronic structure of dithiapyranylidene show a clear evolution towards those of biphenyl as oxidation takes place.
A molecular electron density theory study of the mechanism, chemo- and stereoselectivity of the epoxidation reaction of R -carvone with peracetic acid
2019
The epoxidation reaction of R-carvone 8 with peracetic acid 9 has been studied within the molecular electron density theory at the B3LYP/6-311(d,p) computational level. The chemo- and stereoisomeric reaction paths involving the two C–C double bonds of R-carvone 8 have been studied. DFT calculations account for the high chemoselectivity involving the C–C double bond of the isopropenyl group and the low diastereoselectivity, in complete agreement with the experimental outcomes. The Baeyer–Villiger reaction involving the carbonyl group of R-carvone 8 has also been analysed. A bonding evolution theory analysis of the epoxidation reaction shows the complexity of the bonding cha…
Degradation of Acetylenic Triacylglyceroles and the Inactivation of Membrane Preparations from Moss Protonema Cells
1997
Protonema cells of the moss Ceratodon purpureus accumulate triacylglycerols with two acetylenic fatty acids, 9,12-octadecadien-6-ynoic acid (18:2A) and 9,12,15-octadeca-trein-6-ynoic acid (18:3A), as main components. By following the incorporation of the [14C]-precursors acetate, linoleate, α-linolenate, γ-linolenate, stearidonate and 18:2A, into 18:3A in triacylglycerol accumulating cells, the pathway for acetylenic acids could be established. 18:2A and 18:3A could be synthesized by a second desaturation of the Δ6 double bond of γ-linolenate and stearidonate, respectively. However the major pathway for 18:3A synthesis was via a Δ15 desaturation of 18:2A. Since 18:2A was found exclusively i…
Crystal structure of the chalcone (E)-3-(furan-2-yl)-1-phenylprop-2-en-1-one
2015
The crystal packing of the compound is described by an intermolecular arrangement with the molecules as interlaced layers in a zigzag fashion, denoting interacting self-complementary dimers mainly by the localization of weak hydrogen bonds in a head-to-tail arrangement.
Isolation, structural and toxicological characterization of three new mycotoxins produced by the fungusAureobasidium pullulans.
1993
3 substances, B1, B2, and E1 were isolated from culture medium extracts ofAureobasidium pullulans by reversed phase liquid chromatography and subsequent liquid chromatographic purification steps on silica gel.The 3 compounds inhibited the metabolism ofSaccharomyces cerevisiae and showed toxic effects in the growth inhibition test toEscherichia coli andBacillus subtilis.Elementary analysis and mass spectroscopical methods revealed sum formulas of C23H22O6, C22H20O6 and C24H28O3 for B1 B2, and E1 and molecular weights of 394, 380, and 364, respectively. Mass spectroscopical, UV-, IR-,(13)C-NMR, and(1)H-NMR-spectroscopical investigations revealed polycyclic, non-aromatic compounds containing s…
Stereochemistry of terpene derivatives. Part 4:☆ Fragrant terpenoid derivatives with an unsaturated gem-dimethylbicyclo[3.1.0]hexane system
2005
Abstract Starting from (+)-3-carene 1 several chiral fragrant compounds with the bicyclo[3.1.0]hexane system 4–6 and 10–20 were synthesized. These compounds are structural analogues of naturally occurring fragrant compounds, such as ionones and damascones, and possess either an endo- or an exo-cyclic double bond in the bicyclo[3.1.0]hexane moiety. The absolute configuration of selected products was confirmed by X-ray crystallography and circular dichroism analysis.