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Bonds carbon sigma

The two kinds of covalent bond are not identical, one being a simple covalent bond, a sigma (ct) bond, the other being a stronger (but more reactive) bond called a n bond (p. 56). As in the formation of methane both elements attain noble gas configurations. We can consider the formation of ethene as the linking of two tetrahedral carbon atoms to form the molecule C2H4 represented as ... [Pg.39]

Figure 1.17 The hypothetical formation of the bonding molecular orbitals of ethane from two sp -hybridized carbon atoms and six hydrogen atoms. All of the bonds are sigma bonds. (Antibonding sigma molecular orbitals — are called a orbitals — are formed in each instance as well, but for simplicity these are not shown.)... [Pg.35]

The purpose of this article is to review recent results on the carbonylation chemistry of actinide-to-carbon sigma bonds, bearing in mind the unique properties of 5f-organometallics cited above. We focus our attention on the properties of bis(pentamethylcyclopentadienyl) actinide acyls. Just as transition metal acyls (A) occupy a pivotal role in classical carbonylation chemistry, it will be seen that many of the unusual... [Pg.60]

If hydrogen gas is added to the reaction mixture of J, and 11 the hydrogenolysis reaction of thorium-to-carbon sigma bonds (J-1 22) allows interception of species 13 and thus, catalytic hydrogenation of the inserted carbon monoxide functionality. At 35 C under 0.75 atm initial H2 pressure with [JJ =9.0 x 10" M and [ 1JJ = 6.5 x 10" M, hydrogenation and isomerization are competitive and both the enolate and the alkoxide reduction product 14 are produced (eq.(13)). Under these conditions, turnover fre-... [Pg.72]

This article reviews recent results on the chemical, spectral and structural properties of bis(pentamethylcyclopentadienyl) thorium and uranium dihaptoacyl complexes produced by migratory insertion of carbon monoxide into actinide-carbon sigma bonds. [Pg.80]

Figure 3.12 Carbon sigma hybrids for ctCh bonds (left-hand panels) and Figure 3.12 Carbon sigma hybrids for ctCh bonds (left-hand panels) and <jCc bonds (right-hand panels) in CH4, C2H4, C2H2, and CeH6.
Flood, Thomas C., Stereochemistry of Reactions of Transition Metal-Carbon Sigma Bonds, 12, 37. Floss, Heinz G., Stereochemistry of Biological Reactions at Proprochiral Centers, 15, 253. Freedman, T. B., Stereochemical Aspects of Vibrational Optical Activity, 17, 113. [Pg.596]

In ethylene, there are two types of bonds. Sigma (tr) bonds have the overlap of the orbitals on a line between the two atoms involved in the covalent bond. In ethylene, the C-H bonds and one of the C-C bonds are sigma bonds. Pi (ir) bonds have the overlap of orbitals above and below a line through the two nuclei of the atoms involved in the bond. A double bond is always composed of one sigma and one pi bond. A carbon-to-carbon triple bond results from the... [Pg.150]

Green) Stereochemistry of Reactions of Transition Metal-Carbon Sigma Bonds 9 35... [Pg.488]

An aliphatic metal-carbon sigma bond, e. g., M-CH3, affords a fairly small C chemical shift, sometimes at negative d values. The relatively rare r allyl derivative, PdCl(q allyl)(PHOX), 61 [61], which is related to allylic alkylation chemistry, shows... [Pg.16]

Equations 11, 12, and 13 constitute a process for the formation of the metal-carbon sigma bond. Carbonyl insertion may now occur as shown in Equation 14. [Pg.9]

Synthesis and Reactions of Palladium-Carbon Sigma-Bonded Complexes... [Pg.99]

Tn most organic syntheses involving palladium, palladium-carbon sigma bonds are involved at some stage in the reaction pathway (J). Two important types of reactions which take place in organo-palladium syntheses are oxidative additions to palladium(O) and addition of palladium (II) complexes across olefins as well as the respective reverse (elimination) reactions. In both these reactions, carbon-palladium sigma bonds are made and broken ... [Pg.99]

Palladium (II)-Nucleophile Addition across Olefins. Adding palladium complexes to olefins, either in the presence of an external nucleophile or a ligand which is attached to palladium, produces a palladium-carbon sigma-bonded complex which is not usually isolated in the case of monoolefins. Instead it decomposes and in doing so oxidizes the olefin to an organic carbonyl compound or a vinyl compound, exchanges a substituent group on the olefin, isomerizes the double bond, arylates (alkylates) the olefin, or carboxylates the olefin (2, 3). [Pg.100]

In the case of certain diolefins, the palladium-carbon sigma-bonded complexes can be isolated and the stereochemistry of the addition with a variety of nucleophiles is trans (4, 5, 6). The stereochemistry of the addition-elimination reactions in the case of the monoolefins, because of the instability of the intermediate sigma-bonded complex, is not clear. It has been argued (7, 8, 9) that the chelating diolefins are atypical, and the stereochemical results cannot be extended to monoolefins since approach of an external nucleophile from the cis side presents steric problems. The trans stereochemistry has also been attributed either to the inability of the chelating diolefins to rotate 90° from the position perpendicular to the square plane of the metal complex to a position which would favor cis addition by metal and a ligand attached to it (10), or to the fact that methanol (nucleophile) does not coordinate to the metal prior to addition (11). In the Wacker Process, the kinetics of oxidation of olefins suggest, but do not require, the cis hydroxypalladation of olefins (12,13,14). The acetoxypalladation of a simple monoolefin, cyclohexene, proceeds by trans addition (15, 16). [Pg.100]

One approach to the problem of determining the stereochemistry of the unstable palladium-carbon sigma-bonded intermediate is its trapping by replacement of the palladium with some other group by a reaction that takes place at least competitively with elimination. The carbonylation of such intermediates proceeds more rapidly than the elimination, and it proceeds with 100% retention of configuration at the carbon bearing the palladium (17, 18). [Pg.101]

Doubly bonded carbons are sp2-hybridized. Carbon has three sp2 hybrid orbitals, which lie in a plane and point toward the comers of an equilateral triangle, and one unhybridized p orbital, which is oriented at a 90° angle to the plane of the sp2 hybrids. When two s/r-hybridized carbon atoms approach each other with sp2 orbitals aligned head-on for sigma bonding, the unhybridized p orbitals on each carbon overlap to form a pi bond, resulting in a net carbon-carbon double bond. [Pg.987]

Flood has recently published an excellent contribution which includes a review of the stereochemistry of insertion reactions of CO and S02 into metal-carbon sigma bonds. [Pg.166]

Pi bonds are more reactive than sigma bonds. Carbon, nitrogen, oxygen and sulfur are the only atoms that commonly form re-bonds. Phosphorous forms tc-bonds with oxygen in nucleotide phosphates such asATR... [Pg.11]

As a simple example, let s consider the case of ethane. Rotation about the carbon-carbon sigma bond results in a number of different conformations for this molecule. There are two extremes for these conformations, as shown in Figure 6.4. The eclipsed conformation has each hydrogen on one carbon as close as possible to one hydrogen on the other carbon. The staggered conformation has the hydrogens on one carbon as far from the hydrogens on the other as possible. Other conformations are intermediate between these two extremes. [Pg.186]


See other pages where Bonds carbon sigma is mentioned: [Pg.37]    [Pg.126]    [Pg.38]    [Pg.426]    [Pg.61]    [Pg.59]    [Pg.77]    [Pg.160]    [Pg.155]    [Pg.37]    [Pg.135]    [Pg.8]    [Pg.135]    [Pg.111]    [Pg.1278]    [Pg.13]    [Pg.15]    [Pg.551]    [Pg.128]    [Pg.161]   
See also in sourсe #XX -- [ Pg.54 ]




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Actinide-to-carbon sigma bonds

Bonding sigma bond

Carbon metal sigma bond

Carbon sigma bonds, actinide

Carbon sigma-bonded complexes

Carbon sigma-bonded complexes palladium

Carbon-palladium sigma-bond

Organometallic with metal-carbon sigma bonds

Sigma

Sigma -bonded carbon-backbone

Sigma bond

Sigma bond carbon—oxygen

Sigma-bonding

The Carbon-Metal Sigma Bond

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