Frans-but-2-ene

With palladium—alumina, the products of the reaction of but-l-yne with deuterium [189] were but-l-ene, 99.1% frans-but-2-ene, 0.2% cis-but-2-ene, 0.2% n-butane, 0.5%, until at least 75% of the but-l-yne had reacted. But-l-ene hydrogenation and hydroisomerisation were observed to occur when all the but-l-yne had reacted. The formation of but-2-ene as an initial product was postulated as being the result of a slow isomerisation of but-l-yne to absorbed buta-1 2-diene... 

Metal Temp. (°C) Initial PH2/pC2H2 cis-But -2-ene frans-But -2-ene But-l-ene Selec- tivity... 

The close similarities in the deutero-cis- and deutero-frans-but-2-ene distributions, together with the observation that the frans-but-2-ene but-... 

The formation of but-2-ene and the more highly deuterated cis- and frans-but-2-enes (-d3 and above) were considered to arise from the hydrogenation of adsorbed buta-1 2-diene formed by isomerisation of but-... 

The hydrogenation of buta-1 2-diene appears to have received relatively little attention. Over palladium—alumina at room temperature, the products of the gas phase hydrogenation were c/s-but-2-ene, 52% but-l-ene, 40% frans-but-2-ene, 7% and n-butane, 1% [189]. Some isomerisation of the buta-1 2-diene to but-2-yne (10%) together with traces of but-l-yne and buta-1 3-diene was also observed. A similar butene distribution (namely, cis-but-2-ene 52%, but-l-ene 45% and frans-but-2-ene 3%) was observed in the liquid phase hydrogenation over palladium [186]. 

In the nickel- and cobalt-catalysed reactions [166,207] it was observed that the butene distribution depended upon the temperature of reduction of the catalyst. For both powders and alumina-supported catalysts prepared by reduction of the oxides, reduction at temperatures below ca. 330° C gave catalysts which exhibited so-called Type A behaviour where but-2-ene was the major product and the frans-but-2-ene/cis-but-2-ene ratio was around unity. Reduction above 360° C (Ni) or 440° C (Co) yielded catalysts which gave frans-but-2-ene as the major product (Type B behaviour). It is of interest to note that the yield of cis-but-2-ene was not significantly dependent upon the catalyst reduction temperature with either metal. 

Mechanism A is a generalised mechanism which was proposed for those metals where the frans-but-2-ene cis-but-2-ene ratio was around unity. This mechanism contains a variety of reversible steps which permit the conformational interconversion of the diadsorbed buta-1 3-diene. Consequently, the trans cis ratio will depend upon the relative rates of these reversible steps and the ratio may be much lower than would be expected if the relative surface concentrations of anti- and syn-diadsorbed buta-1 3-diene, species I and III, respectively, in Fig. 37, were similar to the relative amounts of anti- and syn-buta-1 3-diene in the gas phase. It was also suggested that the relative importance of the various steps in mechanism A may be different for different metals. Thus, for example, the type A behaviour of nickel and cobalt catalysts, as deduced from the butene distributions and a detailed examination of the butene AAprofiles [166], was... 

An 11 kJ/mol (2.7 kcal/mol) stability difference is typical between a monosubstituted alkene (but-l-ene) and a trans-disubstituted alkene (frans-but-2-ene). In the following equations, we compare the monosubstituted double bond of 3-methylbut-l-ene with the trisubstituted double bond of 2-methylbut-2-ene. The trisubstituted alkene is more stable by 14 kJ/mol (3.4 kcal/mol). 

Compounds with permanent dipole moments engage in dipole-dipole attractions, while those without permanent dipole moments engage only in van der Waals attractions. cw-But-2-ene and fran -but-2-ene have similar van der Waals attractions, but only the cis isomer has dipole-dipole attractions. Because of its increased intermolecular attractions, m-bul-2-ene must be heated to a slightly higher temperature (4 °C versus 1 °C) before it begins to boil. 

More direct evidence for the formation of difluorocarbene as an intermediate comes from the photolysis of difluorodiazirine in the presence of chlorine, iodine, dinitrogen tetroxide, and nitryl chloride when the corresponding difluoromethane derivatives were formed, and in the presence of isobutene, buta-l,3-diene, and cis- and frans-but-2-ene when the corresponding 1,1-difluorocyclopropane derivatives were formed. Even with considerable excesses of olefins, appreciable tetra-... 

Analysis of ds-but-2-ene/frans-but-2-ene ratios and deuterium distributions allowed the authors to suggest the most favoured conformations of the adsorbed alcohol, which were those with the methyl groups on the same side of the molecule (e.g. Modes 1+3, Scheme 8). 

Alternatively, frans-but-2-ene could be anti-hydroxylated with aqueous peracetic acid. 

Irradiation of the diazocyclohexadienone (108) in the presence of isoprene affords the spiro-adduct (109), whereas the thermally induced reaction gives only (110), which is probably formed via (109) by a vinylcyclopropane rearrangement cf. p. 111). Photolysis if diazomethyltrimethylsilane with frans-but-2-ene gives the trans-cyclopropane (111) (23%) and olefin (112) (61%), consistent with singlet carbene formation. With ethylene, only 17% of cyclopropyl trimethylsilane was obtained, along with 30% of (112). The steric hindrance in tetramethylethylene completely prevented cyclopropane formation, as did electronic effects in fluoro-olefins. No... 

The Lewis acid catalysed addition of propiolate esters to olefins gave cyclobutenes stereospecifically. Thus, cis-but-2-ene and frans-but-2-ene gave 35 % and 31 % yields of isomerically pure cyclobutenes (90) and (9IX respectively, on treatment with methyl propiolate and aluminium trichloride at 25 °C. With 1,2-dimethylcyclohexene, the bicyclo[4,2,0]octene (92) was formed in 72% yield. Use of unsymmetrical olefins such as propene and but-l-ene gave mixtures of regioisomeric cyclobutenes, and 1,1-dialkylated olefins gave ene-addition products. 

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