Mechanical postulates

Berlin green, FeFe(CN)mechanism postulated for the interchange of substituents in trigonal-bipyramidal 5-co-ordinate complexes, e g. PF, and its substituted derivatives. berthoUide compound Solid phases showing a range of composition. 

Starting with the quantum-mechanical postulate regarding a one-to-one correspondence between system properties and Hemiitian operators, and the mathematical result that only operators which conmuite have a connnon set of eigenfiinctions, a rather remarkable property of nature can be demonstrated. Suppose that one desires to detennine the values of the two quantities A and B, and that tire corresponding quantum-mechanical operators do not commute. In addition, the properties are to be measured simultaneously so that both reflect the same quantum-mechanical state of the system. If the wavefiinction is neither an eigenfiinction of dnor W, then there is necessarily some uncertainty associated with the measurement. To see this, simply expand the wavefiinction i in temis of the eigenfiinctions of the relevant operators... 

The two steps in the removal of a particle from the Hquid phase by the filter medium are the transport of the suspended particle to the surface of the medium and interaction with the surface to form a bond strong enough to withstand the hydraulic stresses imposed on it by the passage of water over the surface. The transport step is influenced by such physical factors as concentration of the suspension, medium particle size, medium particle-size distribution, temperature, flow rate, and flow time. These parameters have been considered in various empirical relationships that help predict filter performance based on physical factors only (8,9). Attention has also been placed on the interaction between the particles and the filter surface. The mechanisms postulated are based on adsorption (qv) or specific chemical interactions (10). 

The first possibility envisages essentially the same mechanism as for the second-order process, but with Bt2 replacing solvent in the rate-determining conversion to an ion pair. The second mechanism pictures Bt2 attack on a reversibly formed ion-pair intermediate. The third mechanism postulates collide of a ternary complex tiiat is structurally similar to the initial charge-transfer complex but has 2 1 bromine alkene stoichiometry. There are very striking similarities between the second-order and third-order processes in terms of magnitude of p values and product distribution. In feet, there is a quantitative correlation between the rates of the two processes over a broad series of alkenes, which can be expressed as... 

The mechanism of the K-R reaction has been studied by several groups. " However, the mechanism proposed by Baker and Szell appears to be the most likely pathway. Szell and coworkers agreed with the original mechanism postulated by Baker based on product isolation, spectroscopy and kinetic studies. The o-hydroxyacetophenone 4 is first acylated... 

The three principal concentration mechanisms postulated as being responsible for on-load corrosion processes by Mann are dry-out, concentration in crevices, and concentration in porous deposits. (Clean boiler tube surfaces on which high-pressure water is boiled under forced convection do not develop concentration factors of more than about two.)... 

Detailed kinetic studies in connection with digital simulations do confirm the RR coupling mechanism postulated in older publications as well as the oxidation of the resulting dimer D to the dication D. But the surprising drop in the height of the reduction wave for the redox pair as the concentration... 

Another mechanism postulated to explain the conductometric behavior of these microemulsions attributes it to the transfer of sodium counterions from a reversed micelle to another through water channels opened by intermicellar coalescence [255-258],... 

The mechanism postulated involves rapid, acid-catalysed ligand exchanges to give Cu(thiourea)2 which breaks down in the slow step. Activation energies are... 

Other cyclic compounds such as the N-carboxyanhydrides of a-amino acids,and lactams may be polymerized similarly with regeneration of an amino group at each step. According to the mechanism postulated, the number of polymer molecules formed should equal the number of initiator molecules (e.g., ROH) introduced, and the average number of monomers per polymer molecule should equal the ratio of monomer consumed to initiator. 

Recently Padwa and Battisti reported the photolysis of a 9-heterobicyclo-[3.3.1 Jnonenone system.(60) A mechanism postulating a-cleavage was proposed,... 

Gelman et al. (1978) found that the interaction between lead and phenylhydrazine produced an additive effect in the acute hemolytic phase of anemia and a probable synergistic effect during the compensatory phase of anemia in rabbits. The mechanism postulated for anemic interaction appears to be primarily related to depressed bone marrow production of erythrocytes rather than to increased hemolysis. 

Garratt and Thompson [J. Chem. Soc., 1934, 524, 1817, 1822] have studied the photochemical and thermal decomposition of nickel tetra-carbonyl. Later work by Day, Pearson and Basolo [J. Am. Chem. Soc., 90 (6933), 1968] confirmed that the rate law postulated by Garratt and Thompson was obeyed for the homogeneous process. The mechanism postulated by both groups is ... 

A corresponds roughly to the thiirane geometry, B corresponds to incipient insertion, since a pivoting of the S—H group in the xy plane is calculated to require no further activation energy. The two minima correspond to the two reaction mechanisms postulated from... 

The reaction mechanism postulated by Wolfrom, Schuetz and Cavalieri87 for the formation of 5-(hydroxymethyl)-2-furaldehyde from D-glucose involves the enol (XXXV) of 3-deoxy-D-glucosone as an intermediate an alternative pathway proposed by these same workers included the enol... 

The simplest mechanism postulated for transfer between phases is that a concentration gradient exists only across a stagnant film between phases. Then the rate of transfer is proportional to the interfacial area and a difference of concentrations across the film. For a power law chemical rate, at steady state,... 

Dotz reaction is proposed. According to our calculations the addition of the alkyne molecule to the carbene complex takes place before CO loss in the initial steps of the reaction. Further, our study shows that a novel proposal involving a chromahexatriene intermediate entails lower energy barriers and more stable intermediates than the previous reaction mechanisms postulated by Dotz and Casey. The novel findings query revision of the classically assumed paths and put forward that additional experimental and theoretical studies are necessary to definitely unravel the reaction mechanism of this intringuing reaction. 

Fig. 8.5. Mechanism postulated for competitive, specific base catalyzed hydrolysis and acyl migration of catechol monoesters, as seen with 4-pivaloyl-L-dopa (8.81) [114a]. Deprotonation (Reactions a and b) accelerates intramolecular nucleophilic attack (Reactions c and d) to form a tetrahedral transition state. The latter is postulated to be the intermediate common to hydrolysis (Reaction e) and acyl migration. 

Despite the apparent simplicity of their molecular structure, the metabolism of these agents is chemically so complex, and their routes of bioactivation and inactivation so intimately intertwined, that a detailed and coherent picture of their behavior in the body is not available. The presentation to follow considers first their in vivo de-esterification, and only then the nonen-zymatic and enzymatic mechanisms postulated to be involved. 

Fig. 11.10. Mechanism postulated for activation of formamidines (11.67) as potential prodrugs of anti-HIV nucleoside analogues [103]...

Fig. 11.11. Mechanism postulated for hydrolysis of organic isocyanates involving electrophilic addition of H20 with general base catalysis. The product of hydration is a carbamic acid that spontaneously decomposes to the primary amine with loss of C02 [117].

Fig. 11.13. Mechanism postulated for base-catalyzed dethioacetylation of spironolactone... 

Fig. 11.14. Mechanism postulated for Beckmann-fype dehydration of (Z)-aldoximes (11.103, R = H, R H) catalyzed by cytochrome P450 [132][133]...

Fig. 11.22. Mechanisms postulated for cyclodehydration of a) linear y-hydroxy ketones (11.170) as metabolites of alkanes and alkanones to form 2,5-dialkyl-2,3-dihydrofurans (11.171), and b) piroxicam (11.172) to form its cyclodehydrated metabolite 11.173...

A mechanism has been proposed recently by O Neal and Blumstein for the gas-phase ozone-olefin reaction. This mechanism postulates that molozonide-biradical equilibrium is reached fast and postulates a competition between a-, 8-, and y-hydrogen abstraction reactions and the classical mechanism proposed by Criegee for the liquid-phase reaction. The main features of the Criegee mechanism (Figure 3-9) are the formation, from the initial molozonide, of the major carbonyl products and a second biradical intermediate, the zwitterion. The decomposition pathways of the zwitterion comprise unimolecular re-... 

---