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Carbon bonds about

Figure 3.39 The minimal PSB model, cis-C5/75M7)7 for the PSB photoisomerization. The vertical line indicates the carbon-carbon bond about which the excited state isomerization occurs and defines the two sides used in the definition of the valence bond states. Figure 3.39 The minimal PSB model, cis-C5/75M7)7 for the PSB photoisomerization. The vertical line indicates the carbon-carbon bond about which the excited state isomerization occurs and defines the two sides used in the definition of the valence bond states.
A very rough estimate of the theoretical tensile fracture stress of a fully aligned polymer can be made quite easily by multiplying the strength of a covalent carbon-carbon bond (about 6 x 10 N see, for example Kelly and Macmillan, 1986) by the number of bonds that can be broken by unit area. [Pg.31]

The origin of a torsional barrier can be studied best in simple cases like ethane. Here, rotation about the central carbon-carbon bond results in three staggered and three eclipsed stationary points on the potential energy surface, at least when symmetry considerations are not taken into account. Quantum mechanically, the barrier of rotation is explained by anti-bonding interactions between the hydrogens attached to different carbon atoms. These interactions are small when the conformation of ethane is staggered, and reach a maximum value when the molecule approaches an eclipsed geometry. [Pg.343]

Example I hc reaction coordinate for rotation about the central carbon-carbon bond in rt-bulane has several stationary points.. A, C, H, and G are m in im a and H, D, an d F arc tn axirn a. Only the structures at the m in im a represen t stable species an d of these, the art/[ con form ation is more stable th an ihc nauchc. [Pg.14]

Symmetrical diols can be made by a radical reaction. Radical reactions are rarely much use in carbon-carbon bond formation as they often give poor yields and many products They are of course useful in some FGl reactions in things hke altylic bromination and in functionahsing remote carbon atoms. If rou want to read more about this see Tedder, Part 2, Chapter 11 or Carruthers, Chapter 4. One useful radical reaction is the prnacol reduction ... [Pg.49]

FIGURE 3 4 Potential energy diagram for rotation about the carbon-carbon bond in ethane Two of the hydrogens are shown in red and four in green so as to indicate more clearly the bond rotation... [Pg.107]

Conformational analysis is far simpler m cyclopropane than m any other cycloalkane Cyclopropane s three carbon atoms are of geometric necessity coplanar and rotation about Its carbon-carbon bonds is impossible You saw m Section 3 4 how angle strain m cyclopropane leads to an abnormally large heat of combustion Let s now look at cyclopropane m more detail to see how our orbital hybridization bonding model may be adapted to molecules of unusual geometry... [Pg.114]

Sketch an approximate potential energy diagram similar to that shown in Figures 3 4 and 3 7 for rotation about the carbon-carbon bond in 2 2 dimethylpropane Does the form of the poten tial energy curve of 2 2 dimethylpropane more closely resemble that of ethane or that of butane" ... [Pg.137]

Section 20 21 Acyl chlorides anhydrides esters and amides all show a strong band for C=0 stretching m the infrared The range extends from about 1820 cm (acyl chlorides) to 1690 cm (amides) Their NMR spectra are characterized by a peak near 8 180 for the carbonyl carbon H NMR spectroscopy is useful for distinguishing between the groups R and R m esters (RCO2R ) The protons on the carbon bonded to O m R appear at lower field (less shielded) than those on the carbon bonded to C=0... [Pg.877]

This effect is not simply due to the better packing possible with the branched isomers. The lumpy brcuiched structures impede rotation about the carbon-carbon bond on the main chain, thus giving a stiffer molecule with consequently higher transition temperature. [Pg.422]

The view has also existed in the past that the carbon-silicon bond should be similar in behaviour to the carbon-carbon bond and would have a similar average bond energy. There is some measure of truth in the assumption about average bond energy but because silicon is more electropositive than carbon the C—Si bond will be polar and its properties will be very dependent on the nature of groups attached to the carbon and silicon groups. For example, the CH3—Si group is particularly resistant to oxidation but H13—Si is not. [Pg.816]

The 7t-electron delocalization requires proper orbital alignment. As a result, there is a significant barrier to rotation about the carbon-carbon bonds in the allyl cation. The results of 6-31G/MP2 calculations show the perpendicular allyl cation to be 37.8 kcal/mol higher than the planar ion. Related calculations indicate that rotation does not occur but that... [Pg.281]

Polyisobutylene has a similar chemical backbone to butyl rubber, but does not contain double carbon-carbon bonds (only terminal unsaturation). Many of its characteristics are similar to butyl rubber (ageing and chemical resistance, low water absorption, low permeability). The polymers of the isobutylene family have very little tendency to crystallize. Their strength is reached by cross-linking instead of crystallization. The amorphous structure of these polymers is responsible for their flexibility, permanent tack and resistance to shock. Because the glass transition temperature is low (about —60°C), flexibility is maintained even at temperatures well below ambient temperature. [Pg.584]

Free radicals are initially generated whenever polymer chains are broken and carbon radicals are formed. These effects occur during manufacture and in service life. Many elastomers are observed to oxidize at relatively low temperature (about 60°C), where carbon-hydrogen and carbon-carbon bond cleavages are highly unlikely. It has been demonstrated [52] that traces of peroxides impurities in the rubber cause low-temperature oxidation of rubber. These initiating peroxides are present in even the most carefully prepared raw rubber polymer [53]. [Pg.641]

Huonne specifically weakens the carbon-carbon bond opposite the carbon atom beanng fluonne by about 4-5 kcal/mol per fluonne atom [ 25] It has been shown expenmentally that isomenzation of cir-l, l-difluoro-2,3-dimethylcyclopropane to the trans isomer has an activation energy )of 49 7 kcal/mol [126], which is about 10 kcal/mol lower than that of the parent hydrocarbon [127] (equation 26)... [Pg.922]

Difluorobutane contains two chiral atoms, and can exist as any one of three stereoisomers. Predicting the properties of these molecules is complicated due to the fact that each exists as a mixture of three conformers because of rapid internal rotation about the central carbon-carbon bond. [Pg.69]

Step through the sequence of structures depicting rotation about the carbon-carbon bond in the two dibromoethane isomers l,2-dibromo-l,2-diphenylethane A andfi). For each, plot energy (vertical axis) vs. BrCCBr torsion angle (horizontal axis), and identify all minimum-energy structures. Which of these are reactive conformers , that is, conformers which are set up for either syn or anti elimination of HBr Which are non-reactive conformers , that is, which do not meet the requirements for elimination Do the reactive conformers correspond only to syn elimination, only to anti elimination, or are both pathways represented Which alkene would these reactive conformers lead to Are your results consistent with the observation that each isomer of the starting material gives only one alkene Explain. [Pg.99]


See other pages where Carbon bonds about is mentioned: [Pg.112]    [Pg.202]    [Pg.64]    [Pg.112]    [Pg.202]    [Pg.64]    [Pg.24]    [Pg.156]    [Pg.57]    [Pg.107]    [Pg.108]    [Pg.117]    [Pg.455]    [Pg.40]    [Pg.80]    [Pg.229]    [Pg.61]    [Pg.437]    [Pg.164]    [Pg.384]    [Pg.66]    [Pg.127]    [Pg.136]    [Pg.758]    [Pg.271]    [Pg.95]    [Pg.57]    [Pg.107]    [Pg.455]    [Pg.76]    [Pg.111]    [Pg.271]   
See also in sourсe #XX -- [ Pg.1009 ]

See also in sourсe #XX -- [ Pg.1045 ]




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