Combinational chemistry definition

In the period 1775-1780, Lavoisier established chemistry as a quantitative science by proving that in the course of a chemical reaction the total mass is unaltered. The conservation of mass in chemical reactions proved ultimately to be a death blow to the phlogiston theory. Shortly after Lavoisier, Proust and Dalton proposed the laws of definite and multiple proportions. In 1803 Dalton proposed his atomic theory. Matter was made up of very small particles called atoms. Ever kind of atom has a definite weight. The atoms of different elements have different weights. Compounds are formed by atoms which combine in definite ratios of (usually small) whole numbers. This theory could give a satisfying interpretation of the quantitative data available at the time. 

The elastic and viscoelastic properties of materials are less familiar in chemistry than many other physical properties hence it is necessary to spend a fair amount of time describing the experiments and the observed response of the polymer. There are a large number of possible modes of deformation that might be considered We shall consider only elongation and shear. For each of these we consider the stress associated with a unit strain and the strain associated with a unit stress the former is called the modulus, the latter the compliance. Experiments can be time independent (equilibrium), time dependent (transient), or periodic (dynamic). Just to define and describe these basic combinations takes us into a fair amount of detail and affords some possibilities for confusion. Pay close attention to the definitions of terms and symbols. 

This chapter will cover the efforts that have been made to use the principles of combinatorial chemistry in the development of new catalysts. In the last few years there has been a lively discussion of what is the correct definition of combinatorial chemistry. Some workers reserve the term combinatorial chemistry for the synthesis and evaluation of mixtures. For the purpose of this chapter, we will employ a liberal interpretation of the term. Since one of the definitions of the word combinatorial is, of or involving combinations (14), we will use the term to include what may be referred to as parallel synthesis. In parallel synthesis, one generates a combination of molecules, be they in separate vials or on separate pins. One view may be that a collection of vessels represents a combination of molecules. It is for this... 

The purpose of this brief survey was to demonstrate that, despite the criticisms which may be made of the use of any semi-empirical quantum technique for structural and conformational studies, the CNDO/2 and Extended CNDO/2 formalisms are definitely reliable tools for theoretical conformational analyses in inorganic and coordination chemistry. Moreover, if these tools are combined with the most suitable experimental techniques (i.e. microwave spectroscopy and electron diffraction) in that field, many problems of geometry and conformation can be solved in a way that neither of these approaches could have accomplished alone. 

We deal with two types of numbers in chemistry—exact and measured. Exact values are just that—exact, by definition. There is no uncertainty associated with them. There are exactly 12 items in a dozen and 144 in a gross. Measured values, like the ones you deal with in the lab, have uncertainty associated with them because of the limitations of our measuring instruments. When those measured values are used in calculations, the answer must reflect that combined uncertainty by the number of significant figures that are reported in the final answer. The more significant figures reported, the greater the certainty in the answer. 

As Figure 3 illustrates, redox active guests introduce PET processes almost by definition and luminescent on-off switching is the norm. However, the inhibitions outlined in Section 5 have not prevented the designers of switchable luminescent devices from exploring systems which bind redox active guests. The combined forces of inorganic coordination chemistry and supramolecular science have proved to be too attractive in many of these instances. It is to be hoped that some of this effort will filter across to the examination of more on-off systems like 17 and 18. 

Explosion has several attributes and hence can be described ot defined in different ways- From the standpoint of chemistry it is a rapid cheuircai process resulting in the evolution of gas and heat. To the classic physical definition of a high-pressure energy release must be added thermonuclear effects. Both chemical and physical concepts must be combined to obtain a complete terminology Ref H. Pessiak, Explosivstoffe, 1960, 23—6, 45-7... 

In introductory chemistry courses, much emphasis is necessarily placed on the concept of stoichiometry, that is, the fact that elements combine in certain definite proportions by weight, proportions that reflect their valences and atomic masses. For much of the chemistry of the main group elements and organic compounds, this concept works extremely well, but in transition metal chemistry in particular it is common for ions of more than one oxidation state to form with comparable ease, and sometimes to occur together in the same ionic solid. The presence of more highly oxidized cations... 

Because RME accounts for the mass of all reactants, that is, the actual stoichiometric quantities used, and therefore includes yield and atom economy, this combined metric is probably one of the most helpful metrics for chemists to focus attention on how far from green their current processes actually is. However, like many green chemistry metrics, it does take a little bit of thought to calculate in practice, as one has to work to strict definitions of what to include and what to exclude [46] ... 

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