Bond-forming

All the elements are able to share two electrons forming two covalent bonds. The two covalent bonds formed by oxygen can be separate bonds, for example... 

The large value for fluorine, and the marked decrease from fluorine to iodine, are points to be noted. The high value for fluorine means that the bond between an element M and fluorine is likely to be more ionic (more polar) than a bond formed by M with any other elements. The low value for iodine indicates the possibility that iodine may be electropositive in some of its compounds. 

Hendrickson (14,15] concentrated mainly on C-C bond-forming reactions because the construction of the carbon atom skeleton is the major task in the synthesis of complex organic compounds. Each carbon atom is classified according to which kind of atoms are bonded to it and what kind of bonds ([Pg.184]

To account for barriers of rotation about chemical bonds, i.e., the energetics of twisting the 1,4-atoms attached to the bonds formed by the atoms 2-3, a three-term torsion energy function like that in Eq. (24) is used, in the given form or slightly modified, in almost every force field. 

Synthesis This is part of Kutney s quebrachamine synthesis (J. Amer. Chem. Soc., 1966, 3656). He foimd that if X = OEt, both C-N bond-forming operations could be... 

Isocyanide is isoelectronic with CO and a reactive compound in the presence of Pd catalysts. The heterobicyclic compound 127 is obtained by the successive insertion of 2.6-xylyl isocyanide (126) into the Pd-hydride bond formed from the hydrosilane[121. Aryl isocyanide inserts into the Si—Si bond in oligo-silanes. For example, 3 mol of 2,6-xylyl isocyanide insert into the tetrasilane 128 to give 129[122],... 

Before we descrrbe the bondrng rn methane rt rs worth porntrng out that bondrng theo rres attempt to descrrbe a molecule on the basrs of rts component atoms bondrng theo rres do not attempt to explarn how bonds form Thus the world s methane does not come... 

Section 2 21 Carbon is sp hybridized m acetylene and the triple bond is of the ct + Tt + Tt type The 2s orbital and one of the 2p orbitals combine to give two equivalent sp orbitals that have their axes m a straight line A ct bond between the two carbons is supplemented by two tr bonds formed by overlap of the remaining half filled p orbitals... 

The longest continuous chain that includes the double bond forms the base name of the alkene and the chain is numbered in the direction that gives the doubly bonded carbons their lower numbers The locant (or numerical position) of only one of the dou bly bonded carbons is specified in the name it is understood that the other doubly bonded carbon must follow in sequence... 

There are two different types of carbon-carbon bonds m propene CH3CH=CH2 The double bond is of the ct + tt type and the bond to the methyl group is a ct bond formed by sp -sp overlap... 

The mechanism of free radical polymerization of ethylene is outlined m Figure 6 17 Dissociation of a peroxide initiates the process m step 1 The resulting per oxy radical adds to the carbon-carbon double bond m step 2 giving a new radical which then adds to a second molecule of ethylene m step 3 The carbon-carbon bond forming process m step 3 can be repeated thousands of times to give long carbon chains... 

Carbon-Carbon Bond-Forming Reactions of Organometallic Reagents... 

Hydrolysis of (CH3CHDO)4B in H2O leads to the formation of ethanol retaining the C—D bond formed in the preceding step while forming an O—H bond... 

Aldol condensations are one of the fundamental carbon-carbon bond forming processes of synthetic organic chemistry Furthermore because the products of these aldol con densations contain functional groups capable of subsequent modification access to a host of useful materials is gamed... 

The carbon-carbon bond forming potential of the aldol condensation has been extended beyond the self condensations described in this section to cases in which two different carbonyl compounds react m what are called mixed aldol condensations... 

Use curved arrows to show the carbon-carbon bond forming processes that lead to the four aldol addition products just shown J... 

Like other carbon-carbon bond forming reactions organocuprate addition to enones is a powerful tool m organic synthesis... 

The leader of DuPont s effort was Wallace H Carothers who reasoned that he could reproduce the properties of silk by constructing a polymer chain held together as is silk by amide bonds The neces sary amide bonds were formed by heating a dicar boxylic acid with a diamine Hexanedioic acid adipic acid) and 1 6 hexanediamme hexamethylenedi-amine) react to give a salt that when heated gives a polyamide called nylon 66 The amide bonds form by a condensation reaction and nylon 66 is an example of a condensation polymer... 

Write an equation for the carbon-carbon bond forming step in... 

The carbon-carbon bond forming potential inherent m the Claisen and Dieckmann reac tions has been extensively exploited m organic synthesis Subsequent transformations of the p keto ester products permit the synthesis of other functional groups One of these transformations converts p keto esters to ketones it is based on the fact that p keto acids (not esters ) undergo decarboxylation readily (Section 19 17) Indeed p keto acids and their corresponding carboxylate anions as well lose carbon dioxide so easily that they tend to decarboxylate under the conditions of their formation... 

The critical carbon-carbon bond forming step requires nucleophilic substitution on an alkyl halide by an ester enolate Methyl halides are more reactive than... 

In Its overall design this procedure is similar to the Gabriel synthesis a nitrogen nude ophile IS used m a carbon-nitrogen bond forming operation and then converted to an ammo group m a subsequent transformation... 

The higher terpenes are formed not by successive addition of C5 units but by the coupling of simpler terpenes Thus the triterpenes (C30) are derived from two mole cules of farnesyl pyrophosphate and the tetraterpenes (C40) from two molecules of ger anylgeranyl pyrophosphate These carbon-carbon bond forming processes involve tail to tail couplings and proceed by a more complicated mechanism than that just described... 

A new carbon-carbon bond forms and an entire carboxylic acid group is added to the model... 

IS the key carbon-carbon bond forming step Acetyl coenzyme A (Section 26 1) A thiol ester abbreviated as... 

TT bond (Section 2 20) In alkenes a bond formed by overlap of p orbitals in a side by side manner A tt bond is weaker than a u bond The carbon-carbon double bond in alkenes con sists of two sp hybridized carbons joined by a a bond and a TT bond... 

Double bond (Section 1 4) Bond formed by the sharing of four electrons between two atoms... 

Geometrical Isomerism. Rotation about a carbon-carbon double bond is restricted because of interaction between the p orbitals which make up the pi bond. Isomerism due to such restricted rotation about a bond is known as geometric isomerism. Parallel overlap of the p orbitals of each carbon atom of the double bond forms the molecular orbital of the pi bond. The relatively large barrier to rotation about the pi bond is estimated to be nearly 63 kcal mol (263 kJ mol-i). 

When aqueous solutions of sodium bisulfite are heated with butynediol, one or two moles add to the triple bond, forming sodium salts of sulfonic acids (61). 

Properties of Dense Silicon Carbide. Properties of the SiC stmctural ceramics are shown in Table 1. These properties are for representative materials. Variations can exist within a given form depending on the manufacturer. Figure 2 shows the flexure strength of the SiC as a function of temperature. Sintered or sinter/HIP SiC is the preferred material for appHcations at temperatures over 1400°C and the Hquid-phase densified materials show best performance at low temperatures. The reaction-bonded form is utilized primarily for its ease of manufacture and not for superior mechanical properties. 

The exceUent chemical resistance of acryhc fibers may stem from its unique lateraUy bonded stmcture. Dipole bonds, formed between nitrile groups... 

The principal advantage to this method is that the heat evolved for each carbon—fluorine bond formed, 192.5 kj/mol (46 kcal/mol), is much less than that obtained in direct fluorination, 435.3 kJ/mol (104 kcal/mol). The reaction yields are therefore much higher and less carbon—carbon bond scisson occurs. Only two metal fluorides are of practical use, Agp2 and GoF. ... 

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