Bond forming reactions

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. 

Referring to the effect of electron releasing groups, they suggest that these depress the rate of solvolysis merely because in this SN2 reaction bond-forming is more important than bond-breaking, and electropositive substituents would be expected adversely to affect the bondforming requirements. 

Reaction Bond formed or broken Reaction type Reversible ATP required... 

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]

Next, the power and the benefits of reaction center or reaction sub.structurc searching (see Section 3.3) will be illustrated. Figure 10.3-26 shows some of the hits obtained in a search for reactions that form a C-C bond. Intentionally, only the names of the starting materials and products of these reactions are given in order to emphasize that the common feature of these reactions cannot be derived from coding chemical compounds by name. Only a search by reaction center can expose the similarity in these reactions. The next logical steps would then be to explore whether these reactions have more in common than just forming a C-C bond. 

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

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... 

Self-Rephca.tingSystems. Recently, molecules have been synthesized that can catalyze covalent bond-making reactions by forming a noncovalently bonded superstmcture, a maneuver that converts an intermolecular reaction into an intramolecular one. In general, in such systems, two... 

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. ... 

One of the most useful reactions in forming a P—C bond is the Michaehs-Arbusov reaction, which is a characteristic reaction of tricoordinate phosphoms compounds containing an alkoxy group (22). Alkylation of the electron pair is followed by rearrangement of the initial phosphonium salt. 

The general method by which most newer fluoro quinolones are prepared involves a ring closure reaction to form the quinolone nucleus by forming one of the highlighted bonds, a or b, shown in general stmcture (24). 

The propylene double bond consists of a (7-bond formed by two ovedapping orbitals, and a 7t-bond formed above and below the plane by the side overlap of two p orbitals. The 7t-bond is responsible for many of the reactions that ate characteristic of alkenes. It serves as a source of electrons for electrophilic reactions such as addition reactions. Simple examples are the addition of hydrogen or a halogen, eg, chlorine ... 

Ring Synthesis From Nonheterocyclic Compounds. These methods may be further classified based on the number of bonds formed during the pyridine ring formation. Synthesis of a-picoline (2) from 5-oxohexanenitrile is a one-bond formation reaction (eq. 16) (49). The nitrile is obtained by reaction between acetone and acrylonitrile (50). If both reaction steps are considered together, the synthesis must be considered a two-bond forming one, ie, formation of (2) from acetone and acrylonitrile in a single step comes under the category of two-bond formation reaction. 

Silicon—Carbon Bond-Forming Reactions. After the Rochow-MbUer direct process, the hydro silylation reaction (139),... 

Direct Chlorination of Ethylene. Direct chlorination of ethylene is generally conducted in Hquid EDC in a bubble column reactor. Ethylene and chlorine dissolve in the Hquid phase and combine in a homogeneous catalytic reaction to form EDC. Under typical process conditions, the reaction rate is controlled by mass transfer, with absorption of ethylene as the limiting factor (77). Ferric chloride is a highly selective and efficient catalyst for this reaction, and is widely used commercially (78). Ferric chloride and sodium chloride [7647-14-5] mixtures have also been utilized for the catalyst (79), as have tetrachloroferrate compounds, eg, ammonium tetrachloroferrate [24411-12-9] NH FeCl (80). The reaction most likely proceeds through an electrophilic addition mechanism, in which the catalyst first polarizes chlorine, as shown in equation 5. The polarized chlorine molecule then acts as an electrophilic reagent to attack the double bond of ethylene, thereby faciHtating chlorine addition (eq. 6) ... 

An analogous preparation of thioxopenams from dithiocarbonates (75, R = t-C4H2(CH2)2Si, R = OC H ) has also been described (115). Additionally, an iatramolecular Michael addition reaction to form the [2,3] bond has been exploited ia penem synthesis to prepare FCE 22101 (69) (116). 

Several theories have appeared in the Hterature regarding the mechanism of protection by -PDA antiozonants. The scavenger theory states that the antiozonant diffuses to the surface and preferentially reacts with ozone, with the result that the mbber is not attacked until the antiozonant is exhausted (25,28,29). The protective film theory is similar, except that the ozone—antiozonant reaction products form a film on the surface that prevents attack (28). The relinking theory states that the antiozonant prevents scission of the ozonized mbber or recombines severed double bonds (14). A fourth theory states that the antiozonant reacts with the ozonized mbber or carbonyl oxide (3) in Pig. 1) to give a low molecular weight, inert self-healing film on the surface (3). 

The bonding between carbon monoxide and transition-metal atoms is particularly important because transition metals, whether deposited on soHd supports or present as discrete complexes, are required as catalysts for the reaction between carbon monoxide and most organic molecules. A metal—carbon ( -bond forms by overlapping of metal orbitals with orbitals on carbon. Multiple-bond character between the metal and carbon occurs through formation of a metal-to-CO TT-bond by overlap of metal-i -TT orbitals with empty antibonding orbitals of carbon monoxide (Fig. 1). 

Exothermicity. The catalytic reactions are often exothermic bond-forming reactions of small molecules that give larger molecules. Consequendy, the reactors are designed for efficient heat removal. They may be jacketed or contain coils for heat-transfer media, or the heat of reaction may be used to vaporize the products and aid in the downstream separation by distillation. 

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