C=C Bond (c=c + bond)

Distribution by Scientific Domains
Chemistry77%

Selected Abstracts

Regioselective Addition of Aromatic Amines at the Exocyclic C=C Bond of 2-(2-Oxo-2,3-dihydro-1H-indol-3-ylidene)acetic Acid Esters.

CHEMINFORM, Issue 9 2007
V. O. Koz'minykh
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

Synthesis of Nine-, Ten-, and Fifteen-Membered Alkenolides by the Oxidative Cleavage of the Bridging C=C Bond in 2-Oxabicycloalkenes.

CHEMINFORM, Issue 35 2002
Yu. N. Ogibin
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

ChemInform Abstract: Enantioselective Hydrogenation of the Tetrasubstituted C=C Bond of Enamides Catalyzed by a Ruthenium Catalyst Generated in situ

CHEMINFORM, Issue 34 2001
Philippe Dupau
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Asymmetric Dihydroxylation of ,,,-Unsaturated Carboxylic Esterswith Trisubstituted C=C Bonds , Enantioselective Syntheses of Trisubstituted ,-Butyrolactones

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2006
Tobias Kapferer
Abstract ,,,-Unsaturated esters with stereodefined trisubstitued C=C double bonds were prepared by the Arndt,Eistert homologation of ,,,-unsaturated carboxyl halides, by two-step methoxycarbonylation of allylbarium reagents, by deconjugation of ,,,-unsaturated esters, and by Horner,Wadsworth,Emmons variants of the Stobbe condensation. Sharpless asymmetric dihydroxylation of the ,,,-unsaturated esters, followed by spontaneous cyclization, afforded ,-hydroxy-,-lactones in moderate to good yields and with enantiomeric excesses of up to 97,%. Similarly, tetrahydroxy-,-lactones were obtained from diunsaturated esters; these lactones were converted into a bislactone and an unsaturated ,-hydroxy ,-lactone. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Alternative Mechanistic Paths in the Hetero-Diels,Alder Reaction of ,-Oxothiones: A Theoretical Study

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2007
Laura Legnani
Abstract DFT calculations at the B3LYP/6-311+G(d,p) level for the C, H, and O atoms and at the 6-311+G(2df,p) level for the S atom were used to study the hetero-Diels,Alder reactions between several ,-oxothiones and ethylene or methyl vinyl ether (MVE). All the transition states and the intermediates along the reaction pathways, as well as the reaction products, were located. The reactions with ethylene are all concerted though asynchronous whereas in the reactions with MVE the electron-releasing character of the methoxy substituent lowers the energy barriers and enhances the asynchronicity and the charge transfer process to such an extent that the reaction may become unconcerted and exhibit a two-step mechanism with a zwitterionic intermediate derived from nucleophilic attack of electron-rich MVE to the sulfur atom of the strongly electrophilically activated ,-oxothiones. The reactions are also favored by the conjugation of the newly formed C=C bond. Moreover, the geometric features of the diene exert a nonnegligible role, as dienes that are planar or almost planar in their ground state show a lower energy barrier. Thus, both geometric and electronic features of the dienes as well as of the dienophiles play a significant role in the easiness of the reactions and in their mechanism. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Cycloadditions with Cyclic Seven-Membered Ketene Imines,,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2005
Henry Giera
Abstract The cyclic seven-membered ketene imines 8 , isolable despite ring strain , are available by reactions of thiocarbonyl ylides 3 with 2,3-bis(trifluoromethyl)fumaronitrile (4). In contrast to open-chain ketene imines, 8A,8C underwent (2+2) cycloadditions with ethyl vinyl ether at the C=N double bond; the diastereomeric cycloadducts 10 and 11 were characterized by their spectra, and 10A by X-ray analysis. The corresponding adduct 12 from 8A and 2-methoxypropene easily hydrolyzed to give 14. When 8A,8C were treated with diazomethane, (2+3) cycloadditions took place side by side to the C=C and C=N bond of 8. A supposed adduct at the C=C bond, 18A, lost N2, and 19A was formed which contained a cyclopropylideneamine group; at 50 °C, cheletropic elimination produced the isocyanide 22A. Diazomethane addition to the C=N bond of 8 gave rise to condensed 1,2,3-triazoles 21; the HF elimination from the pyrazolines 20 as primary adducts was probably induced by the excess of diazomethane. The structure of 21B was confirmed by X-ray. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Raman scattering determination of the depth of cure of light-activated composites: influence of different clinically relevant parameters

JOURNAL OF ORAL REHABILITATION, Issue 6 2002
G. Leloup
The purpose of this research was to determine the depth of cure of light-activated composites in relation with different clinically relevant parameters. A Raman spectroscopic method has been used. The measurement of cure is made on a relative basis by comparing the vibration band of the residual unpolymerized methacrylate C=C bond at 1640 cm,1 against the aromatic C=C stretching band at 1610 cm,1 used as an internal standard. The information gained draw attention to the importance of light transmission during the exposure. The influence of sample's thickness on the depth of cure is illustrated by a second order polynomial regression. The shade and translucency of the resin composite also modify the light transmission and thus have a significant influence on the degree of conversion. Moreover the light-source intensity and the distance from the curing tip are important parameters of influence. A significant reduction of the depth of cure is observed for all sample thickness of resin composite tested when using a light device with an intensity of 300 mW cm,2 as well as using a distance from the curing tip higher than 20 mm. [source]

The iso­thio­cyanate complex of tri­phenyl­borane forms an unusual coordination polymer with [K(18-crown-6)]+, both in the solid state and in solution

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2003
Orde Q. Munro
The title salt, (1,4,7,10,13,16-hexa­oxa­cyclo­octa­decane-,6O)[(iso­thio­cyanato)­tri­phenyl­borato-,S]­potassium(I), [K(C19H15BNS)(C12H24O6)] or [K(SCNBPh3)(18-crown-6)], where 18-crown-6 is 1,4,7,10,13,16-hexaoxa­cyclo­octa­decane and [SCNBPh3], is the (iso­thio­cyanato)­tri­phenyl­borate anion, exhibits a supramol­ecular structure that is best described as a helical coordination polymer or molecular screw. This unusual supramolecular structure is based on a framework in which the SCN, ion bridges the chelated K+ ion and the B atom of BPh3 in a ,2 fashion. The X-ray crystal structure of the title salt has been determined at 100,(1) and 293,(2),K. The K+ ion exhibits axial ligation by the S atom of the [SCNBPh3], anion, with a K,S distance of 3.2617,(17),Å (100,K). The trans -axial ligand is an unexpected ,2 -bound C=C bond of a phenyl group (meta - and para -C atoms) that belongs to the BPh3 moiety of a neighboring mol­ecule. The K,C bond distances span the range 3.099,(3),3.310,(3),Å (100,K) and are apparently retained in CDCl3 solution (as evidenced by 13C NMR spectroscopy). By virtue of the latter interaction, the supramolecular structure is a helical coordination polymer, with the helix axis parallel to the b axis of the unit cell. IR spectroscopy and semi-empirical molecular orbital (AM1) calculations have been used to investigate further the electronic structure of the [SCNBPh3], ion. [source]

Effect of Substrate Temperature on the Plasma Polymerization of Poly(methyl methacrylate),

CHEMICAL VAPOR DEPOSITION, Issue 1 2006
B. Casserly
Abstract Low-power, plasma-enhanced (PE)CVD together with polymerization of methyl methacrylate (MMA) can be used to deposit thin films of poly(methyl methacrylate) (PMMA) with,minimal loss of functional groups, as shown by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Raman spectrometry (RS). Retention of functional groups decreases with increased substrate temperature, corresponding to decreased deposition rates. From XPS data, the calculated percentage loss of functional groups ranges from 0.9,% to 43.4,%, changing as a function of deposition conditions. RS confirms the presence of C=C bonds in the polymer backbone as a result of scission of the ester group from MMA. The thermal properties of PECVD-produced films from MMA can be tailored by varying the substrate temperature. Onset of thermal decomposition increases with increased substrate temperature by eliminating thermally labile peroxide linkages in the polymer backbone, and by crosslinking that occurs at radical sites generated via scission of functional group bonds. The post-anneal thicknesses of the remaining polymer is of the order of 4,nm or less, indicating that low-power PECVD of PMMA is a viable candidate to act as a sacrificial material for air-gap fabrication. [source]