Polarizer examples

Molecules of the type AX2E (bent), AX2E2 (bent), and AX3E (trigonal pyramid) are polar. Examples SO HzO, NH3... 

If the excitation electric field is an s-polanzed evanescent field instead of the above p-polarized example, then wH 11 [ = wHJI(z)] does not depend upon p. Therefore, an approximate C(z) can be calculated from the observed fluorescence (P) (obtained experimentally by varying 0) by ignoring the z dependence in the bracketed term in Eq. (7.45) and by inverse Laplace transforming Eq. (7.44) after the ,(0, /J) 2 term has been factored out.,37 39)... 

The dipole moment is a fundamental property of a molecule (or any dipole unit) in which two opposite charges are separated by a distance . This entity is commonly measured in debye units (symbolized by D), equal to 3.33564 X 10 coulomb-meters, in SI units). Since the net dipole moment of a molecule is equal to the vectorial sum of the individual bond moments, the dipole moment provides valuable information on the structure and electrical properties of that molecule. The dipole moment can be determined by use of the Debye equation for total polarization. Examples of dipole moments (in the gas phase) are water (1.854 D), ammonia (1.471 D), nitromethane (3.46 D), imidazole (3.8 D), toluene (0.375 D), and pyrimidine (2.334 D). Even symmetrical molecules will have a small, but measurable dipole moment, due to centrifugal distortion effects. Methane " for example, has a value of about 5.4 X 10 D. 

The induced dipole moment depends on the electric field strength and the structure of the molecule. Charge-induced dipole interactions occur between a charged ion and polarized molecules. A molecule possessing conjugated double bonds is readily polarized. Examples of solutions due to the dipole-induced dipole interaction are benzene in methanol, chloral hydrate in CC14, and phenol in mineral oil. 

Oiganic colloids (mainly humic substances) also possess large specific surfaces and are generally negatively charged due to the acidic functional groups that tend to dissociate or polarize. Examples of such groups include carboxyls (R-COOH), quinones (-Ar=0), phenols (-Ar-OH), and enols (R-CH=CH-OH). (See Section 5.4.2 for a more complete discussion of humic substances.)... 

The stationary phases can differ in polarity. Examples of the most commonly used phases are ... 

Nonpolar solvents Nonpolar solvents are usually hydrocarbon molecules that have an even distribution of charge on the molecule. These are commonly used in organic chemistry and organometallic chemistry because many organic molecules are not polar. Examples include benzene and hexanes. 

The halide complex salts of platinum, chloroplatinites and chloroplatinates, are highly reactive with proteins, with particular affinity for sulphydryl bonds. They can also be histamine liberators (Parrot et al. 1967,1969). These salts thus represent a polar example of a chemical molecule with most of the features which complicate study as allergens. Many of the problems have been resolved and the findings will be given in extenso . Examples of the relevant platinum salts (molecular weight 444 daltons) are ammonium hexachloroplatinate (NH4)2 [Pt Cl ] and te-trachloroplatinate (NH4)2 [PtCm. 

Given the electronegativities of the atoms, arrange a series of bonds in order by polarity. (EXAMPLE 93)... 

Covalent bonds between atoms that have unequal electronegativities are polar. Examples include the H-Cl bond in HCl, the H-O bonds in water, and each of the C-H bonds in methane (CH4). 

Organic compounds with higher molecular weight (up to about 4(X) in the present application) or higher polarity Examples include substituted terpenes and sesquiterpenes, water, oleic acid, glycerol, decanol and saturated lipids up to C12... 

Using the polarity example as mentioned earlier, it can be demonstrated how the various polarity variables are related. The most frequently used McReynolds polarity (MR) served as dependent variable. The following model can be built ... 

Fig. 10 shows the architecture for the weU-known polarity example. There is no need to use all variables to predict the grouping variable for polarity, except four variables DC, MR, Kc, and RP). Selectivity parameters are not necessary for a proper classification (stationary phase no. 21 was misclassified with two hidden neurons two phases (nos. 19 and 20) were misclassified with one hidden neuron). However, one variable DC classifies the phases as slightly, moderately, and highly polar. 

Results of generalized pairwise correlations for the polarity example Dependent variables were (a) MR and (b) XB... 

Type of molecule Point group Structure Fundamentals ] Raman Polarized Examples... 

Some carbon-carbon bond-forming reactions occur with little or no charge polarization. Examples include the Diels-Alder, Cope, and Claisen reactions where concerted bond reorganization occurs (Chapter 5). Others involve transient neutral but electrophilic intermediates, carbenes, and arynes. 

Column chromatography has been employed frequently, using either silica or alumina stationary phases, for isolation of individual anthraquinones. Eluents used for column chromatography usually consist of a series of solvents of increasing polarity. Examples of such separations are found in references (41, 47,119). 

Heteropolar semiconductors There are two or more different kinds of atoms organized regularly in the unit cell. These transfer electrons from one atom to the other and thus have different polarities. Examples of such materials are GaAs and AIN. In such materials the atoms are well organized into a compound (as distinct from a random alloy) with a specific lattice structure. 

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