Search results for "double bond"
showing 10 items of 184 documents
Coordination of copper(II) ions by α,β-dehydro-dipeptides. Potentiometric and spectroscopic study
1991
Abstract Potentiometric and spectroscopic data have shown that the double bond within dehydro-peptides considerably affects their behaviour as ligands relative to their saturated parents, with proton and copper(II) ions.
Theoretical study of the OH addition to the endocyclic and exocyclic double bonds of the d-limonene
2005
Abstract The initial step of the d-limonene + OH gas-phase reaction mechanism was investigated by means of ab initio calculations. We have considered eight different possibilities for the OH addition, corresponding to the two C–C double bonds, the two C atoms of each double bond, and the syn or anti orientation, with respect to the isopropenyl group (endocyclic attack) or the ring cycle (exocyclic attack). Activation energies calculated at the QCISD(T)/6-31G(d)//UMP2/6-31G(d) level, show that there are preferred orientations for the OH addition under atmospheric conditions of temperature and pressure.
Studien zum Vorgang der Wasserstoffübertragung, 68. Die reduktive Überführung aromatischer Säurechloride in Diarylacetylene mit Lithiumamalgam in ein…
1983
Endioldiester A, die durch “Acylierende reduktive Dimerisierung” mit Lithiumamalgam (Li/Hg) nach (1) zuganglich sind, werden mit zwei weiteren Reduktionsaquivalenten nach (2) durch “Reduktive Eliminierung” in Acetylenderivate ubergefuhrt. Hierbei hat sich praparativ das Eintopfverfahren in der Zweistufenarbeitsweise bewahrt. Auch mit Natriumamalgam (Na/Hg) und Kaliumamalgam (K/Hg) gelingt die reduktive Eliminierung nach (2) sowohl von cis- als auch von trans-Endiol-diestern zu Acetylenverbindungen mit guten Ausbeuten. Voraussetzung fur den erfolgreichen Ablauf der Reaktion (2) ist die direkte Verknupfung von zwei Aromaten mit der C C-Doppelbindung in den Endiol-diestern. Endiol-diester mit …
An ELF analysis of the C–C bond formation step in the N-heterocyclic carbene-catalyzed hydroacylation of unactivated C–C double bonds
2012
The changes in electron-density along the C–C bond-formation step in the N-heterocyclic carbene-catalyzed hydroacylation of unactivated double bonds has been studied by an electron localization function (ELF) analysis at the B3LYP/6-31G** level in order to characterize the reaction mechanism. Analysis of DFT reactivity indices and the natural bond orbital and ELF analysis at the most relevant points of the intrinsic reaction coordinate indicate that the reaction path takes place through a two-stage one-step mechanism with non-polar character. In the first stage a hydrogen atom is transferred from the hydroxyl group of Breslow intermediate 12 to the terminal olefinic carbon atom, to yield a …
2,5-Dialkoxysubstituierte Oligo- und Poly(1,4-phenylenethenylen)e
1994
2,5-Dialkoxy Substituted Oligo- and Poly(1,4-phenyleneethenylene)s O-Alkylation and regioselective Rieche formylation of 2-methylhydroquinone (1) yields the 2,5-dialkoxy-4-methylbenzaldehydes 4a–j. The corresponding azomethines 5a–j enter in a strongly alkaline medium a selfcondensation reaction leading to the title compounds 6/7a–j. These conjugated oligomers and polymers possess highly regular structures with exclusively (E)-configurated double bonds. GPC, IR, 1H-, 13C-NMR and MS-FD measurements were used for their characterization. Somewhat different results were obtained for the similarly prepared Schiff base 5l which contains chlorine substituents in the side chains. Cleavage of hydrog…
Reaktionen von Benzothiet mit Iminen
1993
Reactions of Benzothiete with Imines A great variety of compounds 3a–w containing CN double bonds was studied in the reaction with benzothiete (1). H, alkyl, aryl, OR, SR and NR groups can be attached to the imino function. The azomethines 3a–f, the thiazolines 3g–i, the lactim 3n, the oximes 3r–t, the isoxazolinone 3u and the azine 3v show [8π + 2π] cycloaddition reactions yielding derivatives of 1,3-benzothiazine (4a–i, n, r–v). In the case of 4n, s, t secondary reactions occur, initiated by elimination processes. [8π + 2π] Cycloadditions account also for the reactions 3e 10, 11, 3o 18(I), and 3q 19; however, CC double bonds are representing the 2π component in these examples. The thiazol…
Thermal Rearrangements of Perchlorohexatrienes-Structures and Experimental and Theoretical Evaluation of Pathways to Isomerization and Cyclization
2009
We have prepared trans- (1) and cis-octachloro-1,3,5-hexatriene (2) by known routes and studied their thermal behavior experimentally and theoretically by ab initio calculations. The three double bonds in 1 and 2 are completely decoupled due to steric hindrance by the eight Cls, as indicated by calculations as well as the single-crystal X-ray structure of 1. The cis isomer 2 can be isomerized to the trans isomer 1 by heating it to 220–250 °C either neat or dissolved in high-boiling solvents, leading to a roughly 2:1 mixture of trans and cis isomers. Calculations at several different levels of theory predict 1 and 2 to be isoenergetic within 2 kJ mol–1. Unimolecular cis/trans isomerization i…
A green route to synthesize poly(lactic acid)-based macromonomers in scCO2 for biodegradable nanoparticle production
2014
Poly(lactic acid)-based macromonomers, aimed at biomedical applications and with well-defined average chain length, are produced through catalytic ring-opening polymerization of L,L-lactide co-initiated by a co-monomer bearing a double bond. Reactions have been carried out in supercritical carbon dioxide (scCO2) at different temperatures, ranging from 90 to 130 °C. The resulting oligomers have been characterized by different techniques (1H-NMR, 13CNMR, MALDI-TOF, ESI, GPC, FT-IR, TGA), which show that oligomers with narrower molecular weight distribution are produced at the lowest temperature. In addition, a significant reduction of the impact of the secondary reactions has been found at th…
Hetero-Multifunctional Poly(ethylene glycol) Copolymers with Multiple Hydroxyl Groups and a Single Terminal Functionality
2009
Hetero-multifunctional poly(ethylene glycol-co-glycerol) random copolymers with multiple hydroxyl functionalities and a single terminal functionality have been prepared by copolymerization of ethylene oxide (EO) and ethoxy ethyl glycidyl ether (EEGE) with the use of a suitable initiator, introducing a protected amino group or a double bond, respectively. Acidic deprotection was used for removal of the acetal protecting groups in the chain, and the terminal amino group was regenerated by catalytic hydrogenation. A series of copolymers with narrow polydispersity was obtained, varying comonomer fractions from 3 to 67% and molecular weights in the range of 5 000-32 000 g · mol(-1) (1.05 < $\ove…
ChemInform Abstract: Stereoselective Synthesis of 8,12-Furanoeudesmanes from Santonin. Absolute Stereochemistry of Natural Furanoeudesma-1,3-diene an…
2010
Ketobutenolide 3, easily obtained from santonin (1), has been transformed into two natural furanoeudesmanes 4 and 5, isolated from Commiphora molmol and Tubipora musica, respectively. trans- And cis-decalin systems were obtained by stereoselective reduction of the C4−C5 double bond in 3 in the following way: hydrogenation of 3 over Pd/C followed by acidic treatment gave the cis isomer 10 as the major product; selective hydrogenation of the C1-C2 double bond with the Wilkinson’s catalyst followed by reduction with NaTeH yielded mainly the trans isomer 9. Compounds 9 and 10 were transformed into 4 and 5 in parallel sequences. Optical rotation and CD measurements of the synthetic products rev…