Cyclohexene hydrogenation carbon effect

When an alkene reacts with BH3 in THF solution, rapid addition to the double bond occurs three times and a tricilkylborcme, R3B, is formed. For example, 1 molar equivalent of BH3 adds to 3 molar equivalents of cyclohexene to yield tricyclohexylborane. When tricvclohexylborane is then treated with aqueous hydrogen peroxide (H2C>2) in basic solution, an oxidation takes place. The three C-B bonds are broken, -OH groups bond to the three carbons, and 3 equivalents of cyclohexanol are produced. The net effect of the... 

Electronic effects can also influence the ease of double bond hydrogenation. Compounds such as A cyclohexenecarboxaldehyde (4) and other 3-carbonyl substituted cyclohexenes, such as 5 and 6, are more difficult to hydrogenate than the non-carbonyl containing materials. This decrease in activity has been attributed to an interaction between the carbonyl carbon and the 7t cloud of the double bond, shown by 7, which has been termed a supra-annular effect.7-"... 

Reference (70) reports the hydrogenation of 2-propene-l-ol, 2-methyl-3-butene-2-ol, 1-hexene, and cyclohexene on the catalyst 5% Pt/silica gel in a series of 19 solvents. In all these solvents the strongest adsorption was observed for 2-propene-l-ol, the weakest was recorded for cyclohexene. The adsorptivity of 1-hexene was comparable to that of 2-methyl-3-butene-2-ol and varied markedly with the solvent. The weakest adsorptivity of cyclohexene may be assigned to the fact that here in fact we have a disubstituted double bond. By comparing the adsorptivities of 2-propene-l-ol and 1-hexene, it can be seen that the adsorptivity is favorably affected by the presence of the OH group on the a-carbon atom next to the double bond. On the contrary, the adsorptivity of 2-methyl-3-butene-2-ol was weaker, probably due to the steric effect of the methyl groups. 

Aldehydes can be obtained homogeneously from ozonides by reductive cleavage, which can be effected either by zinc in glacial acetic acid or by catalytic hydrogenation of the ozonide118,119 in the presence of a 1 19 palladium-calcium carbonate catalyst.120 Adipdialdehyde has thus been obtained from cyclohexene in 60-70% yield 121... 

Catalysts were prepared by impregnation of Pt inside the pore structure of carbon fibers. Care was taken to eliminate the active metal from the external surface of the support. A very high dispersion of Pt was measured. Four reactions were carried out in a fixed-bed reactor competitive hydrogenation of cyclohexene and 1-hexene, cyclization of 1-hexene, n-heptane conversion and dehydrogenation of cyclohexanol. Three types of carbon fibers with a different pore size and Pt-adsorption capacity along with a Pt on activated carbon commercial catalyst were tested. The data indicate a significant effect of the pore size dimension on the selectivity in each system. The ability to tailor the pore structure to achieve results drastically different from those obtained with established supports is demonstrated with heptane conversion. Pt on open pore carbon fibers show higher activity with the same selectivity as compared with Pt on activated carbon catalysts. 

A carbon attached to a double bond is deshielded due to its sp hybridization and some diamagnetic anisotropy. This effect can be seen in the NMR spectrum of cyclohexene (Fig. 4.12). Cyclohexene has a plane of symmetry that runs perpendicular to the double bond. As a result, we observe only three absorption peaks. There are two of each type of carbon. Each of the double-bond carbons c has only one hydrogen, whereas each of the remaining carbons has two. As a result of a reduced NOE, the double-bond carbons have a lower-intensity peak in the spectrum. 

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