Initial reagent

The alternative approach is to use the computational equivalent of a chemical reaction, or reaction transform. Here, one does not need to define a common template or to generate sets of clipped reagents. Rather, the library can be enumerated using as input the initial reagent structures and the chemical transforms required to operate upon them. In this... 

The pyran 38 is decomposed by acids into the initial reagents,... 

With a non-polar medium, carbon tetrachloride, third-order kinetics were obtained (in the initial reagent concentration range of 4-50 x 10"4 M)749, whereas with a polar medium, methanol, the order with respect to iodine was reduced to one750. 

Until recently, the hydroformylation using palladium had been scarcely explored as the activity of palladium stayed behind that of more active platinum complexes. The initiating reagents are often very similar to those of platinum, i.e., divalent palladium salts, which under the reaction conditions presumably form monohydrido complexes of palladium(II). A common precursor is (39). The mechanism for palladium catalysts is, therefore, thought to be the same as that for platinum. New cationic complexes of palladium that are highly active as hydroformylation catalysts were discovered by Drent and co-workers at Shell and commercial applications may be expected, involving replacement of cobalt catalysts. 

They suggested conducting the reaction at concentrations of the initial reagents, 1-halo-l-nitro-alkane and sodium nitrite, exceeding 1 mol Then, because of the low solubility of molecular oxygen in water (approximately 10 mol L ), the presence of oxygen does not affect the yield of the target product. An increase in the concentration of nitrite ion promotes ter Meer reaction. 

Figure 10.5 Energy profile corresponding to the elementary reaction step transforming the initial reagents Ri +R2 to the products Pi +P2. (From ref. 10.)...

In any case, the initial reagents must be oxidized in the presence of the reaction products, and it is always best if the concentration of products can be increased because it corresponds to a better conversion rate per run—e.g., cyclohexane oxidation must be done in the presence of cyclohexanol and cyclohexanone—and recent advances have increased the amount of conversion per run from 8 to 15% without any loss of selectivity. 

Pietrini and Luisi (2004) described the synthesis of GFP from mixing two or more initial reagents, utilizing water in oil emulsions, see Figure 9.17. This system is biologically less interesting, however, compartments can fuse with each other and they exhibit no leakage. 

A third approach to the construction of an iodine atom photodissociation laser has employed hydrogen iodide as the initial reagent. However, although the primary photolytic process may give rise to a population inversion at the particular wavelength used (A = 2537 A),15,36 the fast secondary reaction... 

The initial reagent for detecting the N-terminal group is an aryl isothiocyanate. R O H R O H R"... 

As can be seen from Fig. 12, the experiment is very well described by Eq. (35). Finally, measurements of the electric conductivity of the binary mixtures of the initial reagents have played an important role in substantiating Scheme (35) 149-152>. The electric conductivity of any binary mixture of the initial reagents (epoxy compounds, TA and alcohol) turned out to be over two orders of magnitude lower than that of the triple system. These experiments show that the interaction of all three reagents is essential for generation of the ionic particles. They have also completely rejected the possibility of formation of active sites directly via interaction of TA with alcohol139,... 

Regio- (Markovnikov) and stereo-specific (anti) incorporation of MeCN (a Ritter-type reaction) has been observed upon bromination of a series of olefins, carried out in this solvent187. The degree of this incorporation depends on the olefin structure and on the initial reagent concentrations and ratios. Thus, when performed at low initial concentrations and with the initial B /alkene ratio >2, this reaction can be used preparatively187. 

When the initial compound was trans stilbene, the unconsummated part was recovered, with no change in configuration. When cis stilbene was employed as the initial reagent, the recovered olefin was a mixture of trans and cis isomers. Hence, the trans con-... 

Methyl-5-(methylamino)-1 //-tctrazolc (401 R = CH3) was used as initial reagent in the synthesis of l,4-bis-[l-methyltetrazol-5-yl]-l,4-dimethyl-2-tetrazene 47, a formal hexamer of diazomethane. The synthetic pathway presumably involves intermediate formation of the corresponding nitrosotetrazole 402 and hydrazinotetrazole 405 (Scheme 48) <2004MI325>. 

A mixture of 0.16g of lutetium monophthalocyaninate acetate and 0.3g of dicyanobenzo-15-crown-5 (DCBC), dried in vacuo, was rafted (melted) in a vacuum glass ampoule, immersed in Wood alloy, at successive increases of temperature from 240 to 260°C. The melted phase was kept at 260°C for 0.5 hr. The molar ratio of the initial reagents Lu salt DCBC was chosen as... 

Clearly the above scheme of liquid-phase oxidation by oxygen shows H202 and ROOH formed as intermediate products. However, they cannot be related to active sites of another, secondary reaction as is customary in, for example, conjugated processes. The reasons for making such comparisons are as follows firstly, H202 and ROOH are final products of a complex reaction and initial reagents for other thermodynamically probable reactions secondly, their formation and consumption (by the scheme selected) do not correspond to the notion of active site of conjugated reactions. 

They have the induction period required for active site accumulation in the system in amounts that cause a noticeable transformation of the initial substance. In both cases (for analysis, refer to the next chapter) the initial reaction is supplementary, just defining the induction period. Hence, the main oxidation reaction proceeds after the induction period, and its stoichiometric equation does not take into account the consumption of initial reagents (as well as consumption of initiators of the induction and initiation period of chain reactions). Thus at the initial stage of oxidation, initiation and auto-catalysis play the role of reaction launchers . 

In fact, in the latter case, the catalyst (injected into the system with initial reagents) only speeds up interaction between the IP of the primary reaction and the acceptor. Therefore, D < v and, consequently, chemical conjugation takes place. This means that no matter how the reaction between the acceptor and the IP is intensified by the catalyst, the induction factor (the determinant) may not exceed v. When analyzing conjugated catalytic reactions, it should be taken into account that the amount of acceptor involved in the reaction may be significantly increased by application of a catalyst in both conjugated reactions. 

---