Direct approach, method

Both HMO calculations and more elaborate MO methods can be applied to the issue of the position of electrophilic substitution in aromatic molecules. The most direct approach is to calculate the localization energy. This is the energy difference between the aromatic molecule and the n-complex intermediate. In simple Hiickel calculations, the localization energy is just the difference between the energy calculated for the initial n system and that remaining after two electrons and the carbon atom at the site of substitution have been removed from the conjugated system ... 

Tomoi and coworkers adopted a somewhat more direct approach in their synthesis of 16-crown-5 derivatives bearing a single alkenyl residue. They hoped to obtain precursors to polymers which could be used as phase transfer catalysts. In this approach I,I-bis-chloromethylethylene (a-chloromethallyl chloride) was allowed to react with the dianion of tetraethylene glycol (NaH/THF). By this method, methylene-16-crown-5 could be isolated in 66% yield after vacuum distillation. Ozonolysis led, in almost quantitative yield, to the formation of oxo-16-crown-5 as shown in Eq. (3.38). These authors prepared a number of other, closely related species by similar methods. 

Two methods are used in practice to obtain enantiomerically pure amino acids. One way is to resolve the racemic mixture into its pure enantiomers (Section 9.8). A more direct approach, however, is to use an enantioselective synthesis to prepare only the desired 5 enantiomer directly. As discussed in the Chapter 19 Focus Oil, the idea behind enantioselective synthesis is to find a chiral reaction catalyst that will temporarily hold a substrate molecule in an unsymmetrical environment. While in that chiral environment, the substrate may be more... 

In the majority of methods described thus far, the interfacial kinetics are deduced by measuring concentration changes in the bulk of the solution rather than at the interface, where the reaction occurs. This introduces a time lag, limiting the resolution of the measurement in the determination of interfacial kinetics. A more direct approach is to identify the interfacial flux. This can be achieved in the electrolyte dropping electrode, via the current flow, but this method is only applicable to net charge-transfer processes at externally polarized interfaces. 

The stated preference method is a direct approach and is used in order to value both use values and non-use values by using a hypothetical market. The choice experiment (CE) and the contingent valuation (CV) methods are the two most common examples of stated preference methods. In the CE method the respondents are asked to choose a level of environmental quality from a set of varying environmental qualities, called choice set. In the CV method the respondent is asked to imagine an environmental market situation and is then asked how she would act in that given situation. CE and CV attempts to find the WTP for a good or service by asking individuals direct questions about their preferences. Alternatively, researchers can ask the respondents for their WTA. 

Directed evolution methods, as well as rational structure-based mutagenesis approaches, have been successful in broadening the substrate tolerance of aldolases. A common goal is to... 

The value of y is known at some time x, and its value is sought at some future time x + delx. The obvious approach, which is called the direct Euler method, is to approximate the function by a straight line of slope yp(x,y(x)) and to calculate the new value of y from... 

My first attempt to calculate the time history of a geochemical system (Section 2.3) used the obvious approach (the direct Euler method) of evaluating the time derivatives and stepping forward. But it was not sue-... 

To overcome the difficulty of inverting the moment equations, Marchisio and Fox (2005) introduced the direct quadrature method of moments (DQMOM). With this approach, transport equations are derived for the weights and abscissas directly, thereby avoiding the need to invert the moment equations during the course of the CFD simulation. As shown in Marchisio and Fox (2005), the NDF for one variable with moment equations given by Eq. (121) yields two microscopic transport equations of the form... 

The leucocyte method estimates pyridoxal phosphate in isolated leucocytes it is based on a coenzyme-catalyzed tyrosine decarboxylase system from S. faecalis (B32). Enough data are not yet on hand to evaluate this method. The determination of circulating or available vitamin Ba should offer a more direct approach. 

The first direct approach requires a long stand of the reaction mixture under high temperature. In the crystal form the product could be receive only after the fermentative splitting of un-reacted glucose. In the further studies [4-6] the direct method was somewhere improved and applied to other mono- and disaccharides, however, there were no principal changes in the synthesis methods. 

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