Carbon-hydrogen bonds tertiary

Fluorine is well known for its ability to fluonnate seleeti vely terttary carbon-h drogen bonds that are slightly activated by polar substituents Hypofluorite reagents also react with carbon-hydrogen bonds, both secondary and tertiary but tertiary bonds react better [6]... 

Fluoroxytiifluorouiethane ettectively fluorinates tertiary carbon-hydrogen bonds in materials with biologieal applications [2 3] (equations 23 and 24)... 

Thermogravimetric data indicate that the structure of a polymer affects stability in a neutral environment (HI). A polymer such as Teflon, with carbon-carbon bonds which are (by comparison) easily broken, and with strong carbon-fluorine bonds, is quite stable thermally. However, polyethylene, also with carbon-carbon bonds but containing carbon-hydrogen bonds which are broken relatively easily in comparison with the carbon-fluorine bond, is less stable than Teflon. In turn, polyethylene is more stable than polypropylene. This difference in stability is probably caused by tertiary carbon-hydrogen bonds in polypropylene. Polypropylene is more stable than polyisobutylene or polystyrene, which decompose principally by unzipping mechanism. 

Only limited success was achieved in determining the relative reactivity of primary, secondary, and tertiary carbon-hydrogen bonds to sulphonyl nitrenes 8>. Insertion of p-toluenesulphonyl nitrene into 2-methylbutane gave a mixture of products which could not be completely resolved. The ratio of (primary) (secondary + tertiary) = [38 + 39 40 + 41] was 1.53, compared to a ratio of 5.6 for carbethoxynitrene58>, indicating the lowered selectivity of the sulphonyl nitrene relative to the carbethoxynitrene, as might be expected from the possible resonance stabilization of the latter species. 

There are not many drugs that are alkynes however, one good example is ethinyl estradiol (Fig. 4.6). Even though ethinyl estradiol is not an aryl alkyne, the acetylenic group is attached to a tertiary carbon and not adjacent to an a-carbon-hydrogen bond. 

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. 

Indeed, it has recently been shown by Rozen [13] that tertiary carbon-hydrogen bonds can be selectively replaced by carbon-fluorine bonds when the reaction is carried out in a polar solvent at low temperature,but it was suggested that an electrophilic process involving a carbocationic transition state is occuring in these instances (see 3.1.1.1). 

Alaimo, P.J.. Arndtsen, B.A. and Bergman. R.G. (2000) Alkylation of iridium via tandem carbon-hydrogen bond activation/decarbonylation of aldehydes. Access to complexes with tertiary and highly hindered metal-carbon bonds. OrganometaUics, 19 (11), 2130-2143. 

D. Gutman, The Controversial Heat of Formation of the tert-C4H9 Radical and the Tertiary Carbon-Hydrogen Bond Energy, Acc. Chem. Res. 1990, 23, 375-380. 

Of prime importance to the continued growth of polypropylene are the stabilizer systems which must be used to protect the resin during processing, and during exposure of finished products to various environmental and use conditions. The weak tertiary carbon—hydrogen bonds in polypropylene make it particularly susceptible to degradation caused by heat, oxidation, process shearing, and ultraviolet radiation (24). 

The phenolic initially gives up its labile hydrogen, which in turn reacts with the various radicals produced in chain reactions then the phenoxy radical becomes stabilized owing to its ability to form resonance structures. The resonance-stabilized forms of the phenoxy radical will not attack tertiary carbon—hydrogen bonds in the polypropylene chain but will react with other radicals such as a peroxide, resulting in the elimination of a second free radical. 

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. 

Dauben, H. J., Jr., McCoy, L. L. N-Bromosuccinimide. II. Allylic bromination of tertiary hydrogens. J. Org. Chem. 1959, 24,1577-1579. Russell, G. A., DeBoer, C. Directive effects in aliphatic substitutions. XVIII. Substitutions at saturated carbon-hydrogen bonds utilizing molecular bromine or bromotrichloromethane. J. Am. Chem. Soc. 1963, 85, 3136-3139. 

The carbon is electrically neutral, but it does have a greater electronegativity than hydrogen, and so it attracts slightly the electrons within the carbon/ hydrogen bonds. Now suggest the relative order of stability of the primary, secondary and tertiary carbon radicals. tertiary>secondary>primary... 

---