Carbon-hydrogen bond reactivity hydrocarbons

Reactivity ratios for all the combinations of butadiene, styrene, Tetralin, and cumene give consistent sets of reactivities for these hydrocarbons in the approximate ratios 30 14 5.5 1 at 50°C. These ratios are nearly independent of the alkyl-peroxy radical involved. Co-oxidations of Tetralin-Decalin mixtures show that steric effects can affect relative reactivities of hydrocarbons by a factor up to 2. Polar effects of similar magnitude may arise when hydrocarbons are cooxidized with other organic compounds. Many of the previously published reactivity ratios appear to be subject to considerable experimental errors. Large abnormalities in oxidation rates of hydrocarbon mixtures are expected with only a few hydrocarbons in which reaction is confined to tertiary carbon-hydrogen bonds. Several measures of relative reactivities of hydrocarbons in oxidations are compared. 

AUhough the main alkylation reactions are thought to occur at or close to the Interface between the acid and hydrocarbon phases (7,15,16), the acid boundary layer at the interface seems more probable. This conclusion is based on the fact that other isoparaffins (including LE s, TMP s, OMH s, and HE s) appear to be much less reactive relative to hydride transfer steps as compared to Isobutane yet many of these Isoparaffins contain one or more tertiary carbon-hydrogen bonds. These heavy isoparaffins are, however, even less soluble in the-acid phase than isobutane. 

The C—H bond is particularly strong and this accounts for the gi eat stability of saturated hydrocarbons and the enormous number of compounds with carbon-hydrogen bonds. Only short chains of Si atoms occur and the links between them are readily broken. There are not many hydrides and they are very reactive. 

The efficient light-initiated decomposition of azides has been the basis for commercially important photoresist formulations for the semiconductor industry. A common approach is to mix a diazide, such as diazadibenzylidenecyclohexanone (I), with an unsaturated hydrocarbon polymer. Excitation of the difunction-al sensitizer produces highly reactive nitrenes which crosslink the polymer by a variety of paths including insertion into both carbon-carbon double bonds and carbon-hydrogen bonds, and by generation of radicals. The polymer component in the most widely used resists is polyisoprene which has been partially eye Iized by reaction with p-toluenesulfonic acid G). Other polymers used include polycyclopentadiene and the copolymer of cyclopentadiene and a-methyI styrene ( ). 

Jones WD, Peher FJ. Comparative reactivities of hydrocarbon carbon-hydrogen bonds with a transition-metal complex. Acc Chem Res. 1989 22 91-100. 

In Section 3.7, we discussed bond dissociation energies for small molecules such as methane and ethane. Now we will extend that discussion to more complex alkanes. Much of the chemical reactivity of hydrocarbons is associated with the carbon-hydrogen bond. The bond dissociation energy, A//°, of the C—H bond of methane is 438 kj mole. In Section 3.7, we saw that this bond dissociation energy is given by the A//° for the following reaction. When we refer to bond dissociation energies, we use the term DH°... 

The need of converting stable hydrocarbons into reactive ones such as olefins makes dehydrogenalion occupy a position of primary importance. Such a reaction is the special case of decomposition in which rupture of a carbon-hydrogen bond occurs. 

Compounds that contain only hydrogen and carbon are called hydrocarbons. The hydrocarbons that have only single bonds all have similar chemistry and they are called, as a family, the saturated hydrocarbons. If there are carbon-carbon double bonds, the reactivity is much enhanced. Hence hydrocarbons containing one or more double bonds are named as a distinct family, unsaturated hydrocarbons. Both saturated and unsaturated hydrocarbons can occur in chain-like structures or in cyclic structures. Each of these families will be considered. 

Many of the characteristic features of hydroalanation of alkenes (reactivities, selectivities) are very similar to those of hydrosilylation. Terminal alkenes react readily in hydroalumination, whereas internal alkenes are much less reactive. Aluminum usually adds selectively to the terminal carbon. Hydroalumination of styrene, however, leads to a mixture of regioisomers.392 When hydroalumination of alkenes is followed by protolysis, saturated hydrocarbons are formed that is, net hydrogenation of the carbon-carbon double bond may be achieved. The difference in reactivity of different double bonds allows selective hydroalumination of the less hindered bond in dienes 393... 

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