A Theoretical Moment

Homberg explored the issue of chemical composition systematically in a series of Essais de chimie presented to the Academy between 1702 and 1709. His approach combined various traditions then known and defies simple characterization. On the one hand, he sought to rehabilitate the doctrine of five principles, by separating them out in actual analysis with the burning glass, a new and more powerful furnace. He thus defined 

Romberg consolidated a distinctly theoretical moment in French elite chemistry. The existing theoretical structure of chemistry—the doctrine of five principles—faced a serious threat from changes in analytic methods and philosophical languages. The chemists of the Paris 

The fortunes of the Paris Academy fluctuated somewhat with the changing ministerial protectors and with Louis XlV s wars. After Colbert s 

Under Bignon s care, the Academy was set on a course of expansion. Fontenelle (1657-1757), a member of the Academie fran aise since 1691, became permanent secretary of the Academie des Sciences in 1697. He had won literary fame with two popular expositions of Cartesian 

Homberg s subsequent presentations to the Academy provide no indication that he continued to work on the subject of plant analysis. In view 

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One mol of 2,6-xylidine is dissolved in 800 ml glacial acetic acid. The mixture is cooled to 10°C, after which 1.1 mol chloracetyl chloride is added at one time. The mixture is stirred vigorously during a few moments after which 1,000 ml half-saturated sodium acetate solution, or other buffering or alkalizing substance, is added at one time. The reaction mixture is shaken during half an hour. The precipitate formed which consists of cj-chloro-2,6-di-methyl-acetanilide is filtered off, washed with water and dried. The product is sufficiently pure for further treatment. The yield amounts to 70 to 80% of the theoretical amount. 

Figure 2 Orbital magnetic moments in bcc-Fe Coi-a . The triangles pointing up-and downwards represent the theoretical moments of Fe and Co, respectively, while the concentration weighted sum is given by circles. Full and open symbols stand for results obtained with and without the OP-term included (SOPR- and SPR-KKR-CPA, resp.). Experimental data [15] for the average magnetic moment (bottom) stemming from magneto mechanical and spectroscopic g-factors are given by full squares and diamonds.

See also the theoretical description of a micro reactor for optical photocatalytic dissociation of non-linear molecules in [140]. Here, a mathematical model for a novel type of micro reactor is given. Rotating non-linear molecules at excitation of valent vibrations are considered, having a magnetic moment. Resonance decay of molecules can be utilized with comparatively weak external energy sources only. 

Let us turn to the results obtained for nitrous oxide N2O. From a theoretical point of view, this is an interesting molecule as properties such as its dipole moment and protonation site have been found very difficult to calculate accurately [14,24], N2O is a linear species whose predicted bond lengths and dipole moment are presented in Table 2. 

A theoretical investigation of the use of NMR lineshape second moments in determining elastomer chain configurations has been undertaken. Monte Carlo chains have been generated by computer using a modified rotational isomeric state (RIS) theory in which parameters have been included which simulate bulk uniaxial deformation. The behavior of the model for a hypothetical poly(methylene) system and for a real poly(p-fluorostyrene) system has been examined. Excluded volume effects are described. Initial experimental approaches are discussed. 

In the Introduction the problem of construction of a theoretical model of the metal surface was briefly discussed. If a model that would permit the theoretical description of the chemisorption complex is to be constructed, one must decide which type of the theoretical description of the metal should be used. Two basic approaches exist in the theory of transition metals (48). The first one is based on the assumption that the d-elec-trons are localized either on atoms or in bonds (which is particularly attractive for the discussion of the surface problems). The other is the itinerant approach, based on the collective model of metals (which was particularly successful in explaining the bulk properties of metals). The choice between these two is not easy. Even in contemporary solid state literature the possibility of d-electron localization is still being discussed (49-51). Examples can be found in the literature that discuss the following problems high cohesion energy of transition metals (52), their crystallographic structure (53), magnetic moments of the constituent atoms in alloys (54), optical and photoemission properties (48, 49), and plasma oscillation losses (55). 

From this point of view, let us wander a little from the subject to discuss briefly the comparison of the computed and experimental values of a dipole moment. Too often, people compare their theoretical results with experimental values obtained in solution, and if there is a discrepancy between the two sets, they generally blame the so-called failure of quantum chemistry to predict dipole moments. 

Considerable effort has gone into solving the difficult problem of deconvolution and curve fitting to a theoretical decay that is often a sum of exponentials. Many methods have been examined (O Connor et al., 1979) methods of least squares, moments, Fourier transforms, Laplace transforms, phase-plane plot, modulating functions, and more recently maximum entropy. The most widely used method is based on nonlinear least squares. The basic principle of this method is to minimize a quantity that expresses the mismatch between data and fitted function. This quantity /2 is defined as the weighted sum of the squares of the deviations of the experimental response R(ti) from the calculated ones Rc(ti) ... 

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