Carbon single bond

We will generate the energies for the carbon-hydrogen bond /fen and the carbon-carbon single bond Hix using the five linear alkanes from ethane through hexane as the five-member data base. The equation to be used is... 

At 146 pm the C 2—C 3 distance m 1 3 butadiene is relatively short for a carbon-carbon single bond This is most reasonably seen as a hybridization effect In ethane both carbons are sp hybridized and are separated by a distance of 153 pm The carbon-carbon single bond m propene unites sp and sp hybridized carbons and is shorter than that of ethane Both C 2 and C 3 are sp hybridized m 1 3 butadiene and a decrease m bond distance between them reflects the tendency of carbon to attract electrons more strongly as its s character increases... 

This makes a carbon-carbon single bond (the new bond appears as a dashed line)... 

The angle formed between successive bonds along the chain backbone—0 in Fig. 1.5a-is not free to assume all values, but is fixed at a definite angle depending on the nature of the bond. For the tetrahedral angle associated with carbon-carbon single bonds, d = 109.5°. 

The limiting parameter to be considered in attempting to develop a satisfactory method for controlling reactions of elemental fluorine is the weakest bond in the reactant compound. For hydrocarbons the average carbon—carbon single-bond strength is 351.5—368.2 kJ/mol (84—88 kcal/mol). The overall... 

Steric Factors. Initially, most of the coUisions of fluorine molecules with saturated or aromatic hydrocarbons occur at a hydrogen site or at a TT-bond (unsaturated) site. When coUision occurs at the TT-bond, the double bond disappears but the single bond remains because the energy released in initiation (eq. 4) is insufficient to fracture the carbon—carbon single bond. Once carbon—fluorine bonds have begun to form on the carbon skeleton of either an unsaturated or alkane system, the carbon skeleton is somewhat stericaUy protected by the sheath of fluorine atoms. Figure 2, which shows the crowded hehcal arrangement of fluorine around the carbon backbone of polytetrafluoroethylene (PTFE), is an example of an extreme case of steric protection of carbon—carbon bonds (29). 

Stereochemistry. Cyclohexane can exist ia two molecular conformations the chair and boat forms. Conversion from one conformation to the other iavolves rotations about carbon—carbon single bonds. Energy barriers associated with this type of rotation are low and transition from one form to the other is rapid. The predominant stereochemistry of cyclohexane has no influence ia its use as a raw material for nylon manufacture or as a solvent. 

The double-bond length in 1,3-butadiene is 0.134 nm, and the ingle-bond, 0.148 nm. Since normal carbon—carbon single bonds are 0.154 nm, this indicates the extent of double-bond character in the middle single-bond. Upon complexing with metal carbonyl moieties like Fe(CO)2, the two terminal bonds lengthen to 0.141 nm, and the middle bond shortens even more to 0.145 nm (18). 

This reaction proceeds by a concerted, [3,3] sigmatropic rearrangement (cf. the Claisen rearrangement) where one carbon-carbon single bond breaks, while the new one is formed. It is a reversible reaction the thermodynamically more stable isomer is formed preferentially ... 

With certain donor substituents at C-3 the experimental findings may be rationalized rather by a diradical mechanism, where formation of the new carbon-carbon single bond leads to a diradical species 6, which further reacts by bond cleavage to give the diene 2 ... 

The Peterson olefination is a quite modern method in organic synthesis its mechanism is still not completely understood. " The a-silyl organometallic reagent 2 reacts with the carbonyl substrate 1 by formation of a carbon-carbon single bond to give the diastereomeric alkoxides 4a and 4b upon hydrolysis the latter are converted into /3-hydroxysilanes 5a and 5b ... 

Carbon-carbon single bonds in alkanes are formed by a overlap of carbon sjy hybrid orbitals. Rotation is possible around a bonds because of their cylindrical... 

Anti conformation (Section 3.7) The geometric arrangement around a carbon-carbon single bond in which the two largest substituents are 180° apart as viewed in a Newman projection. 

There are two plausible reactions which lead to the observed products of the metathesis of alkenes. The first possibility involves cleavage of a carbon-carbon single bond adjacent to the double bond the second involves cleavage of the double bond itself. The following transalkylation... 

However, there are also examples of addition across a strained carbon-carbon single bond, as occurs with bicyclobutane1 and derivatives (Scheme 4.21, Scheme 4.22).180,181 Interestingly, l-cyano-2,2,4,4-letramethylbieylobulane (31) is reported to provide a polykctcniminc (Scheme 4.22).183 This is the only known examples of a a-cyanoalkyl radical adding monomer via nitrogen. 

A unique characteristic feature of the cyclic three-membered ring sulfones and sulfoxides is the dramatic increase in the length of the carbon-carbon single bonds and the carbon-carbon double bonds in the series of thiirane-thiirane oxide-thiirane dioxide (20a -> 16a -> 17a), and thiirene-thiirene oxide-thiirene dioxide (21 -> 18a -> 19b). 

A carbon-carbon double bond is stronger than one carbon-carbon single bond but weaker than the sum of two single bonds (Section 2.15). A carbon-carbon triple bond is weaker than the sum of three carbon-carbon single bonds. Recall that a single C—C bond is a o-bond, but the additional bonds in a multiple bond are TT-bonds. One reason for the difference in strength is that the side-by-side overlap of p-orbitals that results in a rr-bond is not as great as the end-to-end overlap that results in a o-bond. 

The carhon-carbon double bond in alkenes is more reactive than carbon-carbon single bonds and gives alkenes their characteristic properties. As we saw in Section 3.4, a double bond consists of a a-bond and a 7r-bond. Each carbon atom in a double bond is sp2 hybridized and uses the three hybrid orbitals to form three cr-bonds. The unhvbridized p-orbitals on each carbon atom overlap each other and form a Tr-bond. As we saw in Section 3.7, the carbon-carbon 7r-bond is relatively weak because the overlap responsible for the formation of the 7r-bond is less extensive than that responsible for the formation of the a-bond and the enhanced electron density does not lie directly between the two nuclei. A consequence of this weakness is the reaction most characteristic of alkenes, the replacement of the 77-bond by two new a-bonds, which is discussed in Section 18.6. 

The convenience and usefulness of the concept of resonance in the discussion of chemical problems are so great as to make the disadvantage of the element of arbitrariness of little significance. Also, it must not be forgotten that the element of arbitrariness occurs in essentially the same way in the simple structure theory of organic chemistry as in the theory of resonance — there is the same use of idealized, hypothetical structural elements. In the resonance discussion of the benzene molecule the two Kekule structures have to be described as hypothetical it is not possible to synthesize molecules with one or the other of the two Kekule structures. In the same way, however, the concept of the carbon-carbon single bond is an idealization. The benzene molecule has its own structure, which cannot be exactly composed of structural elements from other molecules. The propane molecule also has its own structure, which cannot be composed of structural elements from other molecules — it is not possible to isolate a portion of the propane molecule, involving parts of two carbon atoms... 

It is interesting to note that the unsaturation of a double bond amounts to 0.74 v. e., this being the energy liberated by a reaction leading to the formation of two carbon-carbon single bonds in place of a double bond. For a triple bond the unsaturation is 2.1 v. e. 

The calculated intensity curves are changed in shape only very slightly by changing C=C from 1.34 to 1.38 A., so that the carbon-carbon doublebond distance in these substances cannot be evaluated independently. We think that the value is within 0.02 of 1.34 A. if we were to assume 1.38 A., the values quoted below for the carbon-carbon single-bond distance would be decreased to 1.52 A. for isobutene and 1.53 A. for tetramethylethylene. 

The Constancy of the Carbon-Carbon Single-Bond Distance.—For the eleven hydrocarbons... 

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