Explanation and prediction

Information on nucleophilic addition chemistry of quinones and various mechanistic rationali2ations have been discussed, and molecular orbital calculations have been proposed as more definitive approaches for explanation and prediction (63). 

To further elaborate on this last point, it should be noted that once corpuscular theory is introduced it should provide students with meaningful descriptions, explanations and predictions of macroscopic phenomena and relationships in terms of sub-microscopic entities such as atoms, molecules and electrons. But, alas, according to the foram of experts in chemical education, it does not (Van Berkel et al., 2000). Not only students, but also teachers as well as textbook writers make mistakes with regard to the macro/sub-micro/symbolic levels. Here are some examples mentioned by the international and Dutch fomm. 

By furnishing both explanations and predictions, calculations have not only led to an understanding of experiments that have already been performed on la and lb, but also have motivated new ones. The study of the chemistry of phenylcarbene (la) and phenylnitrene (lb), particularly the ring expansion reaction that each undergoes, thus provides an excellent example of the synergy between calculations and experiments. 

Attitude is a predisposition to act in a certain way. It is the state of readiness that influences a person to act in a given manner (Rahman et al. 1999). Therefore, attitude surveys in agriculture could lead to a more adequate explanation and prediction of farmers economic behavior and have been used on conservation and environmentally related issues focusing on the influence of attitude variables as predictors of conservation behavior (Dimara and Skuras 1999). Dimara and Skuras (1999) concluded from their research that a significant relationship was found between behavior and the goals and intentions of farmers. This relationship is even stronger when statements on attitudes, social norms, and perceived behavioral control are included (Bergevoet et al. 2004)... 

Compared to other chiral separation techniques, the practical importance of CLEC is relatively low because of its complexity. Nevertheless, CLEC is one of the best-investigated techniques from the theoretical point of view. Many theoretical concepts developed in CLEC were of general interest for the explanation and prediction of chiral recognition in all chromatographic systems. 

The three examples in this section are taken largely from the work of our research group. Other, perhaps better, examples of the application of electronic structure calculations to the explanation and prediction of the behavior of RIs could have been selected and some of them are provided in the Suggested Reading Section. 

Physical chemistry and related sciences have played an increasingly important role in the explanation and prediction of physical phenomena which are useful in the production and processing of petroleum. Knowledge of the volumetric and phase behavior of hydrocarbons has so developed that such properties may be predicted with reasonable accuracy at most of the states of interest except those near retrograde dew point. The inability to describe with certainty the composition of many hydrocarbon mixtures in terms of their components places a severe limitation on the prediction of the volumetric and phase behavior of petroleum and of mixtures of its components. 

Chemistry is about what matter is like and how it behaves, and our explanations and predictions of its behaviour. What is matter This word is used to cover all the substances and materials from which the physical universe is composed. There are many millions of different substances known, and all of them can be categorised as solids, liquids or gases (Figure 1.1). These are what we call the three states of matter. 

As is the case with any scientific development with important technological consequences, basic research plays a fundamental role whereby appropriate models are designed to explore and predict the physical and chemical behavior of a system. A confined quantum system is a clear example where theory constitutes a cornerstone for explanation and prediction of new properties of spatially limited atoms, molecules, electrons, excitons, etc. Theoretical study of possible confined structures might also suggest and stimulate further experimental investigations. In essence, the design of novel materials with exceptional properties requires proper theoretical modeling. 

A. A. Petraukas and V. K. Svedas, Hydrophobicity of /3-lactam antibiotics Explanation and prediction of their behavior in various partitiong solvent systems and reversed-phase chromatography, J. Chromatogr., 585 3 (1991). 

What then, can organic chemistry as a science draw out from quantum chemistry In the search for the answer it is useful to look at the already accumulated experience of the interactions in these closely related areas of chemical science. In the last decades there have evolved various methods for the non-empirical and semi-empirical calculations of structure and reactivity of organic molecules based on quantum mechanics. In numerous cases these calculations turned out to be of extreme usefulness in obtaining quantitative information such as the charge distribution in a molecule, the reaction indices of alternate reaction centers, the energy of stabilization for various structures, the plausible shape of potential energy surfaces for chemical transformations, etc. This list seems to include almost all parameters that are needed for the explanation and prediction of the reactivity of a compound, that is, for solving the main chemical task. Yet there are several intrinsic defaults that impose rather severe limitations on the scope of the reliability of this approach. 

The molecular orbitals of the adsorbate and the electronic band structure of the substrate may be complex and often poorly understood. So predicting interactions between the two is nontrivial and inexact. Stated generally, the adsorbate-substrate complex has a different electron distribution from the isolated components, resulting in a different cross section. While the details are usually complex and often undefined, at least one theory of the effects of adsorption on Raman cross section has yielded useful explanations and predictions. The theory attributes chemical enhancement of cross sections to charge transfer between adsorbate and substrate orbitals (or vice versa) and is generally known as charge-transfer theory (1,15,16). 

The wave functions for a particle in a box illustrate another important principle of quantum mechanics the correspondence principle. We have already stated earlier (and will often repeat) that all successful physical theories must reproduce the explanations and predictions of the theories that preceded them on the length and mass scales for which they were developed. Figure 4.25 shows the probability density for the n = 5, 10, and 20 states of the particle in a box. Notice how the probability becomes essentially uniform across the box, and at m = 20 there is little evidence of quantization. The correspondence principle requires that the results of quantum mechanics reduce to those of classical mechanics for large values of the quantum numbers, in this case, n. 

But the interplay of theory with theory is not the important goal of semi-empirical models of quantum chemistry. Explanation and prediction of observed phenomena are. This is the challenge of theory. It makes little difference what calculation is performed today, a better one will be performed tomorrow. But will the better calculation explain phenomena that were, in fact, not already explained by the earlier one Some phenomena are easily explained by the simplest of calculations, and others are not. It makes no sense to pretend otherwise. 

Theoretical understanding of DNA supercoiling. Quantitative explanation and prediction of a variety of DNA topological characteristics, most notably the data on the equilibrium knotting probability and on the equilibrium distribution of ccDNA over topoisomers, demonstrated a remarkable success of the DNA elastic-rod model. The model also proved to be extremely successful in theoretical treatment of the phenomenon of DNA super-coiling. 

An outline of the generalized JTE implications in electronic structure calculations is given showing the importance of this effect in both choosing the method and basis set of ab initio computation and rationalization of the results. The latter aspect is of special importance in transforming computer experiments in theoretical explanation and prediction of molecular properties. As the only source of instability and distortions of any polyatomic system the JTE serves as a general tool of (approach to) problem solving which in electronic structure calculations allow one to make conclusions based on first principles. 

An acceptable fit to the diffractometric data is not the ultimate objective, however. Rather it is the development of a model that possesses a significant measure of validity as the basis for organization, explanation and prediction of experimental observations. With respect to this criterion, the models of cellulose which have been developed so far leave much to be desired, for their capacity to integrate and unify the vast array of information concerning cellulose is limited indeed. One of the objectives of this symposium is to facilitate identification of points of departure for further studies in search of models which are more useful. 

Shamir, B. (1991), The Charismatic Relationship Alternative Explanations and Predictions, Leadership Quarterly, Vol. 2, pp. 81-104. 

The electronic level of properties of solids is of primary importance. This is no mere chance that an important subfield of condensed matter physics and chemistry is focused on the electrons in solids. Basic sciences are fundamentally concerned with understanding and exploiting the properties of interacting electrons and atomic nuclei. With this comes the recognition that, at least in principal, almost all problems of materials can be and should be addressed within quantum theory. An understanding of the behavior of electrons in soUds is essential for explanation and prediction of solid state properties. 

What way is then really truel In the spirit of the philosophical ideas of Poincare, such question is not correct. The second approach is more us l allowing for systematic explanation and prediction of much wider range of phenomena. In other words, the system approach is much more efficient, because it gives the uniform theoretical basis for wider range of phenomena which remain mysterious in the framework of non-system approach. ... 

The explanations and predictions of behavioural science therefore have wider margins of error than those which can be offered by engineers or doctors. Statements made about behaviour will usually be qualified by words such as probably or in general. Individual exceptions to the predictions will always occur. 

Because of its limitations behavioural science is dismissed by some as being no more than common sense dressed up in fancy language. All individuals must have some ability to explain and predict the behaviour of themselves and others, or they would not be able to function effectively in the world. However, most individuals explanations and predictions are often proved wrong. Behavioural science used in a systematic and rigorous way can always improve on unaided common sense. ... 

The analysis of the data collected during interviews provides information about the way students took into account the variables of the model by developing explanations and predictions in relation to the various phenomena and questions. This allows us to draw up the learning pathways that students followed throughout the teaching-learning situations. Some key steps appear in these learning pathways ... 

There is no strong evidence for different levels of understanding of electric circuits between students in case study and baseline groups for both development and transfer phase schools prior to teaching p>0.01 in all cases for explanations and predictions, with the exeeption of predietions in PDDl and PDD2). 

Most individuals explanations and predictions are, therefore, quite often proved wrong. Behavioural science used in a systematic and rigorous way can always improve on tmaided common sense. ... 

A better understanding of the nature and properties of the substances extracted in different maceration conditions will lead to the development and use of mechanical techniques enhancing quality maceration phenomena. In this sector, as in many others, empiricism has preceded research. There is currently no theoretical knowledge of these phenomena that permits the explanation and prediction of the results observed. 

Statistical methods are the mathematical basis for the development of QSAR models. Chemometiic methods (Eriksson et al., 2001) are used to extract information from QSAR data using tools of statistics and mathematics. The applications of these methods are combined with the important goal of explanation and prediction of non-synthesised test compounds. Many different statistical methods are available in the literature and the selection of the appropriate method is critical (Xu and Zhang, 2001). 

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