Properties, quantitative measurement

Non-destructive testing - Radioscopic testing - Part 1 Quantitative measurement of imaging properties, prEN 13068-1... 

The Cahn-Ingold-Prelog (CIP) rules stand as the official way to specify chirahty of molecular structures [35, 36] (see also Section 2.8), but can we measure the chirality of a chiral molecule. Can one say that one structure is more chiral than another. These questions are associated in a chemist s mind with some of the experimentally observed properties of chiral compounds. For example, the racemic mixture of one pail of specific enantiomers may be more clearly separated in a given chiral chromatographic system than the racemic mixture of another compound. Or, the difference in pharmacological properties for a particular pair of enantiomers may be greater than for another pair. Or, one chiral compound may rotate the plane of polarized light more than another. Several theoretical quantitative measures of chirality have been developed and have been reviewed elsewhere [37-40]. 

In Section lA we indicated that analytical chemistry is more than a collection of qualitative and quantitative methods of analysis. Nevertheless, many problems on which analytical chemists work ultimately involve either a qualitative or quantitative measurement. Other problems may involve characterizing a sample s chemical or physical properties. Finally, many analytical chemists engage in fundamental studies of analytical methods. In this section we briefly discuss each of these four areas of analysis. 

Before we are in a position to discuss the viscosity of polymer melts, we must first give a quantitative definition of what is meant by viscosity and then say something about how this property is measured. This will not be our only exposure to experimental viscosity in this volume—other methods for determining bulk viscosity will be taken up in the next chapter and the viscosity of solutions will be discussed in Chap. 9—so the discussion of viscometry will only be introductory. Throughout we shall be concerned with constant temperature experiments conducted under nonturbulent flow conditions. 

The central role of the concept of polarity in chemistry arises from the electrical nature of matter. In the context of solution chemistry, solvent polarity is the ability of a solvent to stabilize (by solvation) charges or dipoles. " We have already seen that the physical quantities e (dielectric constant) and p (dipole moment) are quantitative measures of properties that must be related to the qualitative concept of... 

More complicated and less known than the structure of pure water is the structure of aqueous solutions. In all cases, the structure of water is changed, more or less, by dissolved substances. A quantitative measure for the influence of solutes on the structure of water was given in 1933 by Bernal and Fowler 23), introducing the terminus structure temperature, Tsl . This is the temperature at which any property of pure water has the same value as the solution at 20 °C. If a solute increases Tst, the number of hydrogen bonded water molecules is decreased and therefore it is called a water structure breaker . Vice versa, a Tsl decreasing solute is called a water structure maker . Concomitantly the mobility of water molecules becomes higher or lower, respectively. 

Tables of KA furnish a quantitative measure of acid strengths with which we can compare different acids and predict their properties. Several values of KA are given in Table 11-IV.

In this review recent theoretical developments which enable quantitative measures of molecular orientation in polymers to be obtained from infra-red and Raman spectroscopy and nuclear magnetic resonance have been discussed in some detail. Although this is clearly a subject of some complexity, it has been possible to show that the systematic application of these techniques to polyethylene terephthalate and polytetramethylene terephthalate can provide unique information of considerable value. This information can be used on the one hand to gain an understanding of the mechanisms of deformation, and on the other to provide a structural understanding of physical properties, especially mechanical properties. 

An alternative, single mechanism for both bases may be formulated, however, by taking into account the differences in basicity (piCa = 5.25 and 11.01, for Py and EtsN, respectively [148]), and hydrophobicity between the two bases. A quantitative measure of the latter property is given by logP, the partition coefficient of the solute between n-octanol and water (logP = log([solute] octanol/[solute]water)> 0.65 and 1.45 for Py and EtsN, respectively [149]. This unified mechanism is shown in Fig. 4, where B refers to the base employed. 

All experimental sciences rely on quantitative measurements of properties. Every measurement gives a numerical result that has three aspects a numerical magnitude an indicator of scale, called a unit and a precision. Each aspect is essential, and all three must be reported to make a measurement scientifically valuable. 

Mechanical and chemical methods for qualitative and quantitative measurement of polymer structure, properties, and their respective processes during interrelation with their environment on a microscopic scale exist. Bosch et al. [83] briefly discuss these techniques and point out that most conventional techniques are destructive because they require sampling, may lack accuracy, and are generally not suited for in situ testing. However, the process of polymerization, that is, the creation of a rigid structure from the initial viscous fluid, is associated with changes in the microenvironment on a molecular scale and can be observed with free-volume probes [83, 84]. 

The quest for improved methods for elucidating and predicting the reactive behavior of molecules and other chemical species is a continuing theme of theoretical chemistry. This has led to the introduction of a variety of indices of reactivity some are rather arbitrary, while others are more or less directly related to real physical properties. They have been designed and are used to provide some quantitative measure of the chemical activities of various sites and/or regions of the molecule. 

There is now available a substantial amount of information on the principles and techniques involved in preparing evaporated alloy films suitable for adsorption or catalytic work, although some preparative methods, e.g., vapor quenching, used in other research fields have not yet been adopted. Alloy films have been characterized with respect to bulk properties, e.g., uniformity of composition, phase separation, crystallite orientation, and surface areas have been measured. Direct quantitative measurements of surface composition have not been made on alloy films prepared for catalytic studies, but techniques, e.g., Auger electron spectroscopy, are available. 

The effect of particle size, and hence dispersion, on the coloring properties of aluminum lake dyes has been studied through quantitative measurement of color in compressed formulations [47], It was found that reduction in the particle size for the input lake material resulted in an increase in color strength, and that particles of submicron size contributed greatly to the observed effects. Analysis of the formulations using the parameters of the 1931 CIE system could only lead to a qualitative estimation of the effects, but use of the 1976 CIEL m v system provided a superior evaluation of the trends. With the latter system, the effects of dispersion on hue, chroma, lightness, and total color differences were quantitatively related to human visual perception. 

In general, whenever any quantitative measurement is made the value obtained is only an estimate of the true value of the property being measured. Many factors will cause the value obtained to differ from the true value. These can be summarized as follows ... 

In the second half of the nineteenth century the structural theory of organic chemistry was developed. It led to the concept that chemical, physical and biological properties of all kinds must vary with structural change. The earliest structure-property relationships (SPR) were qualitative. With the development of methods of quantitative measurement of these properties data accumulated. Attempts were then made to develop quantitative models of the structural dependence of these properties. These methods for the quantitative description of structural effects will now be described. 

The authors believe that electron exchange occurs at every intramolecular collision . Thus, their work should provide the first quantitative measurements of the frequency of intramolecular collision between end-groups attached to flexible chains. According to these authors such frequency reflects an intrinsic property of chain molecules, referred to as the dynamic flexibility, which is a measure of the rate of conformational change. It should be distinguished from the static flexibility, which depends on the multitude of... 

To verify such a steric effect a quantitative structure-property relationship study (QSPR) on a series of distinct solute-selector pairs, namely various DNB-amino acid/quinine carbamate CSPpairs with different carbamate residues (Rso) and distinct amino acid residues (Rsa), has been set up [59], To provide a quantitative measure of the effect of the steric bulkiness on the separation factors within this solute-selector series, a-values were correlated by multiple linear and nonlinear regression analysis with the Taft s steric parameter Es that represents a quantitative estimation of the steric bulkiness of a substituent (Note s,sa indicates the independent variable describing the bulkiness of the amino acid residue and i s.so that of the carbamate residue). For example, the steric bulkiness increases in the order methyl < ethyl < n-propyl < n-butyl < i-propyl < cyclohexyl < -butyl < iec.-butyl < t-butyl < 1-adamantyl < phenyl < trityl and simultaneously, the s drops from -1.24 to -6.03. In other words, the smaller the Es, the more bulky is the substituent. The obtained QSPR equation reads as follows ... 

The application of the SVD technique provides a measure of the controllability properties of a given d mamic system. More than a quantitative measure, SVD should provide a suitable basis for the comparison of the theoretical control properties among the thermally coupled sequences under consideration. To prepare the information needed for such test, each of the product streams of each of the thermally coupled systems was disturbed with a step change in product composition and the corresponding d3mamic responses were obtained. A transfer function matrix relating the product compositions to the intended manipulated variables was then constructed for each case. The transfer function matrix can be subjected to SVD ... 

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