Bond in hydrocarbons

Double bonds in hydrocarbons are indicated by changing the suffix -ane to -ene, and triple bonds are indicated by... 

Although the —CH2— group could be inserted in other places, the free rotation about single C—C bonds in hydrocarbons allows the resulting molecules to be twisted into one or the other of these two isomers. Both compounds are gases, but butane (24) condenses at —1CC, whereas methylpropane (25) condenses at — 12°C. Two molecules that differ only by rotation about one or more bonds may look different on paper, but they are not isomers of each other they are different conformations of the same molecule. Example 18.3 illustrates how to tell if two molecules are different isomers or different conformations of the same isomer. 

Ionic Dissociation of Carbon-Carbon a- Bonds in Hydrocarbons and the Formation of Authentic Hydrocarbon Salts... 

Ionic dissociation of the carbon-carbon a bond in hydrocarbons 184... 

To sum up, in addition to the electronic stabilization and solvation, classical steric congestion caused by either the cation or anion moieties effectively controls the ease of ionic dissociation of the carbon-carbon a bond in hydrocarbons. 

Spectroscopy of the PES for reactions of transition metal (M ) and metal oxide cations (MO ) is particularly interesting due to their rich and complex chemistry. Transition metal M+ can activate C—H bonds in hydrocarbons, including methane, and activate C—C bonds in alkanes [18-20] MO are excellent (and often selective) oxidants, capable of converting methane to methanol [21] and benzene to phenol [22-24]. Transition metal cations tend to be more reactive than the neutrals for two general reasons. First, most neutral transition metal atoms have a ground electronic state, and this... 

One common feature of all M + hydrocarbon systems mentioned in Sec. 1.2.2 is that none of the products resulted from cleavage of a C-C bond. This is a result of several factors. First, C-H bonds are less directional than C-C bonds (Sec. 1.1), allowing for multicentered bonding at the transition state, which tends to lower the barrier for C-H insertion relative to C-C insertion.2,18,22 Second, since M-H bonds are usually stronger than M-C bonds, intermediates resulting from insertion into a C-H bond are usually thermodynamically favored.141 Third, there are typically more C-H bonds in hydrocarbons than C-C bonds, so C-H insertion is also statistically favored. Finally, C-H bonds are more accessible to an incoming metal atom and are therefore more susceptible to insertion. 

Ionic dissociation of carbon-carbon a-bonds in hydrocarbons and the formation of authentic hydrocarbon salts, 30, 173 Ionization potentials, 4, 31 Ion-pairing effects in carbanion reactions, 15, 153 Ions, organic, charge density-NMR chemical shift correlations, 11,125 Isomerization, permutational, of pentavalent phosphorus compounds, 9, 25 Isotope effects, hydrogen, in aromatic substitution reactions, 2,163... 

The properties of some boron hydrides along with those of other volatile hydrides are shown in Table 13.2. A very interesting reaction that diborane undergoes is one in which it reacts with double bonds in hydrocarbons. The reaction can be shown as... 

The comparison of the BDE of hydrocarbons and amines proves the strong effect of the amino group on the BDE of the a-C—H bond. This is the result of the strong interaction of the a-C atom free valence of the aminoalkyl substituent with the p-electron pair of nitrogen atom. The energy of such interaction demonstrates the difference in the BDE of the a-C—H bond in hydrocarbons and amines (AD = Dc h(RCH3) — Dc H (RNH2)). 

Each of these bond enthalpies is an average enthalpy, measured from a series of similar molecules. Values of AH, . for, say, C-H bonds in hydrocarbons are likely to be fairly similar, as shown by the values in Table 3.3. The bond energies of C-H bonds will differ (sometimes quite markedly) in more exceptional molecules, such as those bearing ionic charges, e.g. carbocations. AH, . values differ for the OH bond in an alcohol, in a carboxylic acid and in a phenol. 

FIGURE 8.14 Critical sooting equivalence ratio l c at 2200K as a function of the number C—C bonds in hydrocarbon fuels. +, 0, and - indicate ethane/l-octane mixtures in molar ratios of 5 to 1, 2 to 1 and 1 to 2, respectively x, acetylene/benzene at a molar ratio of 1 to 3. The O symbol for 2 to 1, falls on top of the butene symbol. 

For the anodic substitution of unactivated CH-bonds, some fairly selective reactions for tertiary CH-bonds in hydrocarbons and y—CH-bonds in esters or ketones are available [85-87]. However, in some cases, a better control of follow-up oxidations remains to be developed. Chemically, a number of selective reactions are available, such as the ozone on silica gel for tertiary CH-bonds [88], the Barton or Hoffmann-LoefHer-Freytag reaction for y-CH-bonds [89], and for remote CH-bonds, Cprop)2NCl/H [90, 91], photochlorination of fatty acids adsorbed on alumina [92] or template-directed oxidations [93]. 

Michael additions to benzotriazole-stabilized carbanions have been reviewed. review of the structural dependence of heterolytic bond dissociation energy of carbon-carbon a-bonds in hydrocarbons has summarized the synthesis and behaviour of molecules in which highly stable cationic and anionic hydrocarbon moieties have apparently been combined. 

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