Carbon-methyl bonds

Similarly, of the low-energy staggered conform-ers, there will be two equivalent ones where the carbon-methyl bonds are inclined at 60° to each other, and one in which the carbon-methyl bonds are inclined at 180°. We can also predict that the latter conformer, which has the methyl groups as far away from each other as possible, will be of lower energy than the alternative staggered... 

Apparently, the torsional strain resulting from eclipsing a carbon-hydrogen bond with a carbon-methyl bond is only 1.2 kJ (0.3 kcal) more than the strain of eclipsing two PROBLEM-SOLVING carbon-hydrogen bonds. 

A further peculiarity of saturated hydrocarbons is that they can be branched. At the simplest level methyl, ethyl, isopropyl and tert-butyl groups need to be considered as examples of primary to quaternary carbon centres, whose increasing branching has important consequences. They have an internal conformational analysis—about each carbon-methyl bond—as well as the analysis of the bond to the rest of the molecule. 

Atomic Carbon.—Skell and Plonka have extended their studies of the chemistry of atomic carbon, which they generate in a low-intensity carbon arc. The mechanism of the conversion of carbon-hydrogen bonds to carbon-methyl bonds has been investigated thoroughly the detection of triplet carbenes as intermediates infers that the inserting carbon atoms are in the state. 

The protonation of an alkylaromatic molecule occurs at its ipso position (eq. 1). This weakens the carbon — methyl bond and initiates transfer to a second aromatic molecule (eqs. 2 and 3). Transfer of a proton back to the zeolite from the protonated xylene gives the xylene product and regenerates the acid site in the catalyst (eq. 4). 

In the acid catalyzed dehydration of 2 methyl 1 propanol what carbocation would be formed if a hydride shift accompanied cleavage of the carbon-oxygen bond in the alkyloxonium lon" What ion would be formed as a result of a methyl shift" Which pathway do you think will predominate a hydnde shift or a methyl shift" ... 

Secondary alkyl halides react by a similar mechanism involving attack on benzene by a secondary carbocation Methyl and ethyl halides do not form carbocations when treated with aluminum chloride but do alkylate benzene under Friedel-Crafts conditions The aluminum chloride complexes of methyl and ethyl halides contain highly polarized carbon-halogen bonds and these complexes are the electrophilic species that react with benzene... 

Rotation about the carbon-nitrogen bond is slow in amides The methyl groups of NJ dimethylformamide are nonequivalent because one is cis to oxygen the other cis to hydrogen... 

The dimsyl ion also adds to carbon—carbon double bonds, and if the mixture is heated for several hours, methanesulfenate is eliminated. The overall result is methylation, and for compounds such as quinoline or isoquinoline (eq. 20), yields ate neady quantitative (50). The reaction sequence for isoquinoline to 1-methyhsoquinoline is as follows ... 

Diazoalkanes add to the carbon-carbon double bonds of 2,3-diphenylthiirene 1-oxide and 1,1-dioxide. The adducts lose SO or SO2 to give pyrazoles and related compounds (Scheme 103) (80CB1632). Mesoionic oxazolones (75CLH53), 4-methyl-5-phenyl-l,2-dithiolene-3-thione (80JOU395) and pyrylium betaines (72JOC3838) react similarly via intermediate adducts (Scheme 104). Enamines (Scheme 96) and ynamines add to the double bond of 2,3-diarylthiirene 1,1-dioxides to give acyclic and cyclic sulfones by a thermal. 

With very few exceptions, the pine resin acids belong to four basic skeletal classes abietane, pimarane, isopimarane, and labdane (Fig. 7). The acids of the abietane, pimarane and isopimarane series have a isopropyl or methyl/ethyl group in the carbon-13 position and a single carboxyl group in the carbon-18 position, and differ only in the number and location of the carbon-carbon double bonds (the most common have two carbon-carbon double bonds). The acids of labdane series are less common and contain one carboxyl group in the carbon-19 position. 

The common pine resin acids based on the pimarane and isopimarane skeletal (pimaric-type acids) are shown in Fig. 9. The pimarane and isopimarane acids series differ only in the methyl group position in the carbon-13 position. Isopimaric and sandaracopimaric acids differ in the location of the carbon-carbon double bond. 

In striking contrast to the above observations is the finding that both reduction and reductive methylation of the tetrahydropyranyl ether of 17a-ace-toxypregnenolone (71) afford the expected products (72a, b) in 85-88 % yields by direct crystallization of the crude reaction products. Clearly, the complications in the reduction of the 16-en-20-one system are attributable primarily to reactions of the carbon-carbon double bond rather than to the a-carbanion (73), which is the final intermediate in both the reduction of the 16-dehydro compounds and the 17-acetoxy ketones. 

House investigated the role of cuprous ions in the conjugate addition of organometallic reagents. He found that the catalytic effect can be explained by the intervention of a methyl copper derivative, which reacts rapidly with the carbon-carbon double bonds of the conjugated system. 

Consequently rotation about the carbon-nitrogen bond constitutes exchange of the methyl protons between nonequivalent sites, analogous to cis-trans isomerization ... 

The separation of mixtures involving N-methyl-JLtetrahydropyridines into their pure components by means of gas-liquid chromatography was discussed in a report by Holik et al. (87). They found that, using tris(/3-cyanoethoxymethyl)-y-picoline as the stationary phase, the primary factors involved in the specific retention volumes of these enamines is the electronic effect of a methyl substituent and the nitrogen atom on the carbon-carbon double bond. It was observed that 1,3-dimethyl-Zl -tetrahydropyridine (141) has a smaller specific retention volume and, hence, is eluted before... 

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