Optional Site Selectivity Selected Examples

Schlosser introdueed the eoneept of optional site selectivity through mechanism-based substrate reagent matching to describe the metalation of arenes carrying two different DMGs 

TABLE 26.2 Selected Directed Metalation Groups (DMGs) 

Carbon-Based DMGs Heteroatom-Based DMGs  

Cl Fort [94] OSOjNR, Sli SOjNLiR, SOjNR SOjNIiC(Me)jPh P(0)(01i Snieckus [95] Martin [96] Hauser [97] Snieckus [74] Lopez-Ortiz [98,99] 

OCONR2 0P(0)(NEt2)2 S02f-Bu SOf-Bu CONR2 CONLiR SO2NR2 SONLiR 

---

Heterosubstituted Arenes. As a rule of thumb, the super-basic n-BuLi/f-BuOK reagent having coordinatively saturated lithium preferentially deprotonates such positions where charge excess is most efficiently stabilized. This may result in a different regiochemical behavior with respect to simple organolithium reagents exploiting the so-called optional site-selective metalation. Some representative examples of n-butyllithium/potassium ferf-butoxide metalations of heterosubstituted arenes are shown in Table 5. 

When dealing with flammable materials, the selection from the inherently safer design options may vary according to the site and process. For example,... 

A class of sedative/hypnotic type drug that exert their effects through the benzodiazepine binding site on GABAa receptors. The class consists both of molecules that contain the benzodiazepine moiety, for example diazepam, lorazepam and flunitrazepam, and the newer, non-benzodiazepine compounds such as zolpidem, zopiclone, indiplon and zaleplon. BzRAs are primarily used for the treatment of anxiety, insomnia and to elicit varying levels of sedation. The wide selection of compounds currently available affords the prescribing clinician extensive options in terms of relative efficacies and durations of action. 

In this section, we present two examples with different scenarios. The first example illustrates the performance of the model on a single site total refinery planning problem where we compare the results of the model to an industrial scale study from Favennec et al. (2001). This example serves to validate our model and to make any necessary adjustments. The second example extends the scale of the model application to cover three complex refineries in which we demonstrate the different aspects of the model. The refineries considered are of large industrial-scale refineries and actually mimic a general set-up of many areas around the world. The decisions in this example include the selection of crude blend combination, design of process integration network between the three refineries, and decisions on production units expansion options and operating levels. 

Use Tools Offered by the Search Engine This includes using the Help button. Also, it is helpful to try the more like this , related searches , or narrow your search options offered by some search engines. Advanced search options often help to eliminate sites that are unlikely to provide the desired information. For example, the advanced search option on Google allows selection or exclusion of specific types of URL, such as .com sites. 

In cases where high purity hydrogen is valued, dense metal membranes are an attractive option over polymeric membranes and porous membranes that exhibit much lower selectivities. Two examples where this is true are low-temperature fuel cells (e.g., proton exchange membrane fuel cells [PEMFCs] and alkaline fuel cells [AFCs]) and hydrogen-generating sites where the product hydrogen is to be compressed and stored for future use. 

A significant seasonal temperature variation and low negative temperatures in the winter season (from plus 35°C to minus 55°C) in the candidate Russian sites for the UNITHERM NPP, located in the remote regions of Russia, predetermine the selection of a specific coolant in the independent circuit. The proposed options are, for example, ammonia, alcohol or ethylene glycol. 

---