Initiated reaction

Fig. XVIII-22. Schematic illustration of the steps that may be involved in a surface-mediated reaction initial adsorption, subsequent thermalization, diffusion and surface reaction, and desorption. (From Ref. 199 copyright 1984 by the AAAS.)...

Drukker, K., Hammes-Schiffer, S. An analytical derivation of MC-SCF vibrational wave functions for the quantum dynamical simulation of multiple proton transfer reactions Initial application to protonated water chains. J. Chem. Phys. 107 (1997) 363-374. 

Bam ford-Stevens Reaction- initial conversion of a tosylhydrazone to a diazo intermediate... 

Aldehydes are important because they are temporary reservoirs of free radicals (see eqs. 11 and 12). HCHO is a known carcinogen. Nitric acid is formed by OH attack on NO2 and by a dark-phase series of reactions initiated by O3 + NO2. Nitric acid is important because it is the second most abundant acid in precipitation. In addition, in southern California it is the major cause of acid fog. 

Particles are the major cause of the ha2e and the brown color that is often associated with smog. The three most important types of particles produced in smog are composed of organics, sulfates, and nitrates. Organic particles are formed when large VOC molecules, especially aromatics and cycHc alkenes, react with each other and form condensable products. Sulfate particles are formed by a series of reactions initiated by the attack of OH on SO2 in the gas phase or by Hquid-phase reactions. Nitrate particles are formed by... 

Another very important reaction initially involving nucleophilic attack on an aldehyde carbonyl is the Wittig reaction. An yUd adds to the carbonyl forming a betaine intermediate which then decomposes to produce an olefin and a tertiary phosphine oxide. 

Carbon and Graphite. Fluorine reacts with amorphous forms of carbon, such as wood charcoal, to form carbon tetrafluoride [75-73-0], CF, and small amounts of other perfluorocarbons. The reaction initiates at ambient conditions, but proceeds to elevated temperatures as the charcoal bums ia fluoriae. 

More recent work reports the onset of thermal degradation at lower temperatures and provides a clearer picture of the role of oxygen (73—75). In the presence of oxygen, backbone oxidation and subsequent cleavage reactions initiate decomposition. In the absence of oxygen, dehydrofluorination eventually occurs, but at significantly higher temperatures. 

The reaction with fluorine occurs spontaneously and explosively, even in the dark at low temperatures. This hydrogen—fluorine reaction is of interest in rocket propellant systems (99—102) (see Explosives and propellants, propellants). The reactions with chlorine and bromine are radical-chain reactions initiated by heat or radiation (103—105). The hydrogen-iodine reaction can be carried out thermally or catalyticaHy (106). 

Initiation of radical reactions with uv radiation is widely used in industrial processes (85). In contrast to high energy radiation processes where the energy of the radiation alone is sufficient to initiate reactions, initiation by uv irradiation usually requires the presence of a photoinitiator, ie, a chemical compound or compounds that generate initiating radicals when subjected to uv radiation. There are two types of photoinitiator systems those that produce initiator radicals by intermolecular hydrogen abstraction and those that produce initiator radicals by photocleavage (86—91). 

Alkyl hydroperoxides are among the most thermally stable organic peroxides. However, hydroperoxides are sensitive to chain decomposition reactions initiated by radicals and/or transition-metal ions. Such decompositions, if not controlled, can be auto accelerating and sometimes can lead to violent decompositions when neat hydroperoxides or concentrated solutions of hydroperoxides are involved. 

The hydrolysis and polycondensation reactions initiate at numerous sites within the TMOS/H2O solution as mixing occurs. When sufficient intercoimected Si—O—Si bonds are formed in a region, the material responds cooperatively as colloidal (submicrometer) particles or a sol. The size of the sol particles and the cross-linking within the particles, ie, the density, depends on the pH and R ratio, where R = [H2 0]/[Si(0R)4]. 

Styrene is a colorless Hquid with an aromatic odor. Important physical properties of styrene are shown in Table 1 (1). Styrene is infinitely soluble in acetone, carbon tetrachloride, benzene, ether, / -heptane, and ethanol. Nearly all of the commercial styrene is consumed in polymerization and copolymerization processes. Common methods in plastics technology such as mass, suspension, solution, and emulsion polymerization can be used to manufacture polystyrene and styrene copolymers with different physical characteristics, but processes relating to the first two methods account for most of the styrene polymers currendy (ca 1996) being manufactured (2—8). Polymerization generally takes place by free-radical reactions initiated thermally or catalyticaHy. Polymerization occurs slowly even at ambient temperatures. It can be retarded by inhibitors. 

Monitor reaction initiation and progress during charging... 

First it is important to study how the gradual conversion of soda will influence the rate of reaction. Initially, keep all other conditions constant that can influence the rate oxygen and water concentration, and the mole fraction of TCE in the reactor. This last is the same as the TCE in the discharge flow from the reactor. 

Hydrocarbon radicals, predominantly through the reaction, initiate the prompt mechanism... 

This polymer first appeared commercially in 1965 (Parylene N Union Carbide). It is prepared by a sequence of reactions initiated by the pyrolysis of p-xylene at 950°C in the presence of steam to give the cyclic dimer. This, when pyrolysed at 550°C, yields monomeric p-xylylene. When the vapour of the monomer condenses on a cool surface it polymerises and the polymer may be stripped off as a free film. This is claimed to have a service life of 10 years at 220°C, and the main interest in it is as a dielectric film. A monochloro-substituted polymer (Parylene C) is also available. With both Parylene materials the polymers have molecular weights of the order of 500 000. 

Merck chemists have done a detailed investigation on the effect of reaction conditions on the yield and selectivity of the Friedlander reaction. Initially, the... 

Similarly, methyl propiolate and methyl phenylpropiolate give the cyclazine (67) and its 2-phenyl derivative, respectively, as would be expected of reactions initiated through a Michael addition to the acetylenic ester. 

Ring Transformation Reactions Initiated by Nucleophilic Attack. 284... 

The reaction of a cyclic ketone—e.g. cyclohexanone 1—with methyl vinyl ketone 2 resulting in a ring closure to yield a bicyclic a ,/3-unsaturated ketone 4, is called the Robinson annulation This reaction has found wide application in the synthesis of terpenes, and especially of steroids. Mechanistically the Robinson annulation consists of two consecutive reactions, a Michael addition followed by an Aldol reaction. Initially, upon treatment with a base, the cyclic ketone 1 is deprotonated to give an enolate, which undergoes a conjugate addition to the methyl vinyl ketone, i.e. a Michael addition, to give a 1,5-diketone 3 ... 

The allylic bromination of an olefin with NBS proceeds by a free-radical chain mechanism. The chain reaction initiated by thermal decomposition of a free-radical initiator substance that is added to the reaction mixture in small amounts. The decomposing free-radical initiator generates reactive bromine radicals by reaction with the N-bromosuccinimide. A bromine radical abstracts an allylic hydrogen atom from the olefinic subsfrate to give hydrogen bromide and an allylic radical 3 ... 

The allylic position of olefins is subject to attack by free radicals with the consequent formation of stable allylic free radicals. This fact is utilized in many substitution reactions at the allylic position (cf. Chapter 6, Section III). The procedure given here employs f-butyl perbenzoate, which reacts with cuprous ion to liberate /-butoxy radical, the chain reaction initiator. The outcome of the reaction, which has general applicability, is the introduction of a benzoyloxy group in the allylic position. 

Pyridinium chloride ([PyHjCl) has also been used in a number ofcyclization reactions of aryl ethers (Scheme 5.1-4) [4, 18]. Presumably the reaction initially proceeds by deallcylation of the methyl ether groups to produce the corresponding phenol. The mechanism of the cyclization is not well understood, but Pagni and Smith have suggested that it proceeds by nucleophilic attack of an Ar-OH or Ar-0 group on the second aromatic ring (in a protonated form) [4]. 

Wilkes and co-workers have investigated the chlorination of benzene in both acidic and basic chloroaluminate(III) ionic liquids [66]. In the acidic ionic liquid [EMIM]C1/A1C13 (X(A1C13) > 0.5), the chlorination reaction initially gave chlorobenzene, which in turn reacted with a second molecule of chlorine to give dichlorobenzenes. In the basic ionic liquid, the reaction was more complex. In addition to the... 

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