Alkane bonds

G. Farrell, T. J. Burkey. How Strong are Metal-Alkane Bonds Separation ofThermal and Molecular Contributions to Photoacoustic Signals Using High Pressure. Abstr. Pap. Am. Chem. Soc. 1994, 208, 523-INOR. 

One of the most popular nitroxide-based radicals (TEMPO) has been shown to abstract H-atoms from activated C—H bonds. However, the nitroxide itself is easily photo-degraded, hi order to examine more photochemically stable alternatives to TEMPO in abstraction reactions, the related isoindoline nitroxide radical (61) has been examined.116 Abstractions from unactivated primary, secondary, and tertiary C—H alkane bonds were all achieved. 

B is correct. The bonds are stabilized by resonance and are shorter and stronger than carbon-carbon alkane bonds but longer and weaker than carbon-carbon alkene bonds. 

The term oxidative cyclization is based on the fact that two-electron oxidation of the central metal occurs by the cyclization. The same reaction is sometimes called reductive cyclization . This term is based on alkene or alkyne bonds, because the alkene double bond in 13 is reduced to the alkane bond 14, and the alkyne 15 bond is reduced to the alkene bond 16 by the cyclization. Cyclizations of alkynes and alkenes catalyzed by transition metal complexes proceed by oxidative cyclization. In particular, low-valent complexes of early transition metals have a high tendency to obtain the highest possible oxidation state, and hence they react with alkynes and alkenes forming rather stable metallacycles by oxidative addition or oxidative cyclization. 

Carbonyl radicals in a polymer arise through a radical oxidation of aldehyde groups. The comparison of the rate of transfer reaction of methyl radical to tertiary alkanes and to aldehydes is more favorable for aldehydes which are by one to two orders more reactive [89]. The concentration of aldehyde groups in an oxidized polymer is usually considerably lower than that of alkane bonds C—H. The course of decarbonylation becomes therefore significant only in such a case when further oxidation occurs in highly oxidized microregions. As a random reaction taking place in the polymer bulk it is less probable. 

Carbonyl group Alcohol group Alkane bonds Alkene bonds... 

Alkenes are different from alkanes, however, in a number of ways. First, their bonds are different, as indicated by their suffixes. As you will recall, the -ane ending tells you that alkane compounds are joined by single bonds. The -ene ending for alkenes tells you that these compounds have one or more double bonds. A double bond involves four bonding electrons between two carbon atoms, instead of the two bonding electrons in all alkane bonds. Examine Figure 13.18 to see how the presence of a double bond affects the number of hydrogen atoms in an alkene. 

Rh-CsHs complex - first characterization of compound with metal-alkane bonding... 

Key properties of noble gases are summarized in Table 1 other properties are in refs. 6 and 11. The formation and detection of M-Ng bonds provide many of the same challenges as for transition metal-alkane bonds. Comparison of spectra and energetics of species such as Cr(CO)5Xe and Cr(CO)s(alkane) points to further similarities in bond enthalpies. Recent reviews tackle complexes of alkanes in detail . Since investigations of alkane complexes are more frequent than those of xenon complexes, we may use these results to anticipate the formation of further M-Ng bonds [e.g., to HMn(CO)4]. 

TABLE 11.1 Representative Bond Enthalpies for Metal-Alkane Bonds for Substrates Coordinated to Metal Pentacarbonyl Fragments, M(CO)s6... 

No isolable and fully characterized examples of a transition metal complex with a coordinated alkane have been reported. With typical metal-alkane bond energies <15kcal/mol, isolation of these complexes is a substantial challenge. However, spectroscopic methods have been incorporated to directly observe alkane coordination. Initially, fast IR methods were utilized to study transient alkane coordination. More recently, novel NMR techniques have been developed to directly observe the coordination of alkanes to transition metals. Both techniques have afforded valuable insight into metal-hydrocarbon bonding. 

The nature of the species obtained upon alkane bond cleavage. 

Reactions of Alkanes Bond-Dissociation Energies, Radical Halogenatlon, and Relative Reactivity... 

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