Selection, selectivity

Selectivity selective selective selective universal selective universal/... 

Transportation links Ul Select Select Select Select... 

Method Residence Temperature Conversion Selectivity Selectivity Selectivity time ( C) (%) of ofMTM ofTFA... 

THF) unselective unselective unselective selective selective selective... 

Name any one-atom, two-atom, three-atom, or four-atom selection with the Select/Select command. 

To average or plot a structural quantity, the structural quantity must first be selected and named by the normal process for creating named selections (select the atoms and then use the menu item Select/Name Selection to give the selected atoms a name). Erom then on the Molecular Dynamics Averages dialog box will show these named selections as possible candidates to be averaged or plotted in addition to energetic quantities described above. 

Selectivity Selectivity is rarely a problem in molecular absorption spectrophotometry. In many cases it is possible to find a wavelength at which only the analyte absorbs or to use chemical reactions in a manner such that the analyte is the only species that absorbs at the chosen wavelength. When two or more species contribute to the measured absorbance, a multicomponent analysis is still possible, as shown in Example 10.6. 

Selectivity Selectivity in voltammetry is determined by the difference between half-wave potentials or peak potentials, with minimum differences of+0.2-0.3 V required for a linear potential scan, and +0.04-0.05 V for differential pulse voltammetry. Selectivity can be improved by adjusting solution conditions. As we have seen, the presence of a complexing ligand can substantially shift the potential at which an analyte is oxidized or reduced. Other solution parameters, such as pH, also can be used to improve selectivity. 

Catalyst Selectivity. Selectivity is the property of a catalyst that determines what fraction of a reactant will be converted to a particular product under specified conditions. A catalyst designer must find ways to obtain optimum selectivity from any particular catalyst. For example, in the oxidation of ethylene to ethylene oxide over metallic silver supported on alumina, ethylene is converted both to ethylene oxide and to carbon dioxide and water. In addition, some of the ethylene oxide formed is lost to complete oxidation to carbon dioxide and water. The selectivity to ethylene oxide in this example is defined as the molar fraction of the ethylene converted to ethylene oxide as opposed to carbon dioxide. 

There are two general temperature poHcies increasing the temperature over time to compensate for loss of catalyst activity, or operating at the maximum allowable temperature. These temperature approaches tend to maximize destmction, yet may also lead to loss of product selectivity. Selectivity typically decreases with increasing temperature faster deactivation and increased costs for reactor materials, fabrication, and temperature controls. 

Positional Selectivity. Selective attachment of a group by a reaction at only one of several possible locations. Synonymous with "rcgioselectivity. ... 

Calculate the compression ratio, Pd/Ps = P2/P1 = Pc-From Table 12-9B for the compressor frame selected, select polytropic efficiency, Cp, and using Figure 12-65A, determine adiabatic efficiency, e d. 

Though the syn-l,3-diol relationship is ultimately established in the reductive decyanation vide infra), the alkylation is itself highly selective. Selectivities are typically greater than 100 1 in favor of the axial nitrile. This selectivity can be rationalized by a chair-like intermediate 15 (Scheme 3) for which equatorial alkylation is highly favored on steric grounds. Approach of the electrophile from an axial trajectory leads to a syu-pentane-like interaction. 

The highly dispersible calix[4]arene neutral carriers can also improve the durability for neutral-carrier-type ion sensors. Time-course changes in both sensitivity (slope for Na+ calibration graph) and selectivity (selectivity coefficient for Na" " with respect to K+) were followed in the Na -ISFETs based on ion-sensing membranes of silicone rubber-(l), plasticized PVC-(l), and plasticized PVC-(2) (Fig. 2). Deterioration proceeded quite quickly in the Na -ISFETs of plasticized PVC-(2) both the Na+ sensitivity and selectivity... 

Price, D. K. 1996. Sexual selection, selection load and quantitative genetics of zebra finch bill colour. Proc. R. Soc. Lond. B 263 217-221. 

An improved RAPT sequence utilizing frequency-switched Gaussian pulses (FSG-RAPT) was later proposed [68], This method also allows for the measurement of Cq values. The dependence of the FSG-RAPT enhancement on offset frequency for nuclei with different CgS has been exploited to design pulse schemes for the selective selection of nuclei with large quadrupole couplings [69-71]. 

---