Critical discussion

The DN scale has historical merits. It was among the first attempts to establish Lewis base strength quantitatively. It was widely used in the field of solution, coordination and organic chemistry to describe the Lewis basicity of solvents. However, after 40 years of use, convergent critical analyses have pointed out the serious limitations of DN. They concern (i) the choice of SbCls as a reference Lewis acid, (ii) the sample of Lewis bases studied, (iii) the quality of calorimetric measurements and (iv) the domain of validity of the scale. 

The choice of SbCls appears unfortunate for technical and theoretical reasons. From the experimental point of view, SbCls catalyses the reaction of chlorinated solvents with amines, which prevents the easy and accurate study of this very important class of nitrogen bases. In the same way, the frequently used solvent hexamethylphosphoric triamide does not give reliable results with SbCls. From the perspective of the theoretical prediction of DN, the 136 electrons of SbCls and the position of Sb in the fourth row of the periodic table make quantum chemical calculations on a series of SbCls complexes difficult. Semi-empirical PM3 calculations of complexation enthalpies have been performed [38] on SbCls complexes with 12 bases. At this low calculation level, only 43% of the variance of gas-phase calculated enthalpies is explained by experimental enthalpies in CH2CICH2CI. At the ab initio or DFT level, we are aware of only two studies the first [39] on five nitriles and pyridine and the second [40] on H2S complexes with SbCls. For the pyridine-SbCls complex, the gas-phase enthalpy, calculated without BSSE, is -115.5 kJ moF while the experimental value in CICH2CH2CI amounts to —142.3 kJ mol . It must be noted that antimony is described with the use of an effective core potential that incorporates major relativistic effects. In the end, the nature of the Sb—B dative bond does not seem to have been studied in depth and no theoretical prediction of the SbCls affinity can easily be made for Lewis bases. 

Concerning the sample of bases, the chemical variety is very low since 90% of them are oxygen bases. There is a serious lack of sp - and sp -hybridized nitrogen bases, and the carbon tt bases, the halogen bases and the sulfur bases are totally missing. 

In addition, a number of the calorimetric measurements seem rather unreliable, probably because of the experimental problems caused by the high reactivity and catalytic effects of SbCls, or because the complexation was incorrectly assumed to be complete for weak bases. 

For the above reasons, we discourage the use of the DN scale when precise and robust scales are available. In particular, the affinity scale constructed with the reference Lewis acid BF3 is an alternative for measuring the strength of dative bonds. This scale is presented 

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CRV737) A critical discussion of the mechanisms of ring-opening of epoxides by nucleophiles. 

Because of low prices and steadily rising performance on the part of technical and standard plastics, the application of natural fibers came to a near halt. The current critical discussion about preservation of natural resources and recycling led to a reflection about natural materials, the focus centuring on regrowing raw materials [2]. 

Acknowledgement. I thank many colleagues in the battery industry for critical discussions, for sugges-... 

We express our thanks to Drs. Z. Knor and Z. Bastl for stimulating critical discussions on the manuscript. In addition, we are grateful to Dr. V. Cermik for kindly enabling one of us (M. S.) to take time off for the work on the present contribution. 

Recently, Engel et al.92 critically discussed these models and concluded by equilibrium measurements in different solvents that bridging of the hydroxy group of hydroxyproline by means of a water molecule must be an unspecific reaction and can be caused as... 

In the following paragraphs we present a critical discussion of the factors that govern the competition between heterolytic and homolytic dediazoniation, before... 

The only author to postulate a homolytic mechanism in the last few decades was Deng (1989). His arguments are based on the formation of small amounts of fluorinated bi- and polyphenyls in thermal fluoro-de-diazoniations and in mass-spec-trometric degradations of benzenediazonium tetrafluoroborate and its substituted derivatives. However, he does not include a critical discussion of his work. 

Less detailed information is available concerning the rates of reactions of most hydroxy salts of inorganic acids indeed, the qualitative changes occurring during stepwise or overall removal of water have not been established for many systems. The behaviour characteristics of a number of hydroxy halides are mentioned below, as are the dehydroxylations of representative minerals. Some aspects of the relationships between the reactions of minerals and structurally similar metal hydroxides are critically discussed by Brett et al. [92]. 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

C, E curves have been obtained for Zn(0001) andZn(lOTO) at various crci with different additions of tu.630,634-636 The data for Zn(0001) at Cju = const have been used to obtain C"1, Ql plots. Nonlinear plots have resulted, with the value of the reciprocal slope remarkably dependent on ctu- At c-ru = 0 1 M, the reciprocal slope of the PZ plot is 1.1, increasing with decreasing c-ru Such an effect has been related to the weak specific adsorption of OH" on Zn. This explanation has been critically discussed by Vorotyntsev,74 who has assumed that the effect635,636 is connected with the variation in the compact layer composition of the Z11/H2O + TU interface as cjv varies. 

Observations that have been made will be critically discussed in the light of their relevance to other approaches that attempt to elucidate mechanistic features of this complex phenomenon. No claim is made for a complete coverage of the literature, but an attempt has been made to collate all relevant information and to discuss the results that best illustrate the principles involved. 

Evans and Baranyai [51, 52] have explored what they describe as a nonlinear generalization of Prigogine s principle of minimum entropy production. In their theory the rate of (first) entropy production is equated to the rate of phase space compression. Since phase space is incompressible under Hamilton s equations of motion, which all real systems obey, the compression of phase space that occurs in nonequilibrium molecular dynamics (NEMD) simulations is purely an artifact of the non-Hamiltonian equations of motion that arise in implementing the Evans-Hoover thermostat [53, 54]. (See Section VIIIC for a critical discussion of the NEMD method.) While the NEMD method is a valid simulation approach in the linear regime, the phase space compression induced by the thermostat awaits physical interpretation even if it does turn out to be related to the rate of first entropy production, then the hurdle posed by Question (3) remains to be surmounted. 

The Expert Report is a particular requirement of the European pharmaceutical regulatory system. It is intended that the Expert Report submitted by the applicant should include an accurate summary of the supporting evidence for the application and that it should also include a critical discussion of that information. Expert reports were originally required when a requirement for an Assessment Report was imposed on the member states the intention was that the Expert Report should form the basis for that Assessment Report. 

Haydon, D. A., and B. S. Hladky, Ion transport across thin lipid membranes a critical discussion of mechanisms in selected systems, Quart. Rev. Biophys., 5, 187 (1972). 

Critical discussion of the results so far available on biogenesis indicates that we still do not know which of these three will lead to the most convincing answers to the many questions which still remain unanswered. 

The critical discussion of some aspects of Eigen s theories and hypotheses by no means diminishes the great merits which Manfred Eigen has gained in more than 30 years of work in this area of science. His experimental and theoretical contributions to the question of the evolution of genetic information are of decisive importance, even if corrections of his theories may be necessary from time to time. 

Of the protozoa in which flavins have been proposed to serve as photoreceptor pigments for behavioral responses, Euglena has been the most intensely studied. In this contribution a survey is given of the historical studies of photomovement in this organism, followed by a critical discussion of the experimental conditions under which such studies might be carried out. 

A review on the chemistry of 1,2,4-thiadiazoles, which gives a critical discussion of methods of synthesis and is accompanied by experimental procedures, appeared in Science of Synthesis <2004HOU277>. An annual review of... 

GFAAS end analysis of Pb in blood was critically discussed in a review, including methods of introducing the sample into the furnace, matrix interferences and ways of improving the precision of the method, such as use of a stabilized temperature platform40. An evaluation program was carried out for quality control materials and proficiency for... 

This book is to a certain extent a summary of both scientific results of various authors and of classes in biogeochemistry and ERA, which were given to students by the author during recent years in different universities. So I would like to thank the many students of the Universities of Cornell, Moscow, Pushchino, Seoul, and Bangkok, who explored this subject initially without a textbook. The critical discussion and comments during these classes have provided me the possibility of presenting this book. 

The present volume of the series focuses on the interplay between organisms and the physical chemistry of the environmental media in which they live. It critically discusses the different physicochemical and biophysical features of the kinetics of processes at the biointerface, with special attention given to aspects such as bioavailability of chemical species, analysis of the necessary mass transfer towards/from the biointerface, routes of transfer through the biomembrane, etc. This volume was realised within the framework of the activities of the former IUPAC Commission on Fundamental Environmental Chemistry of the Division of Chemistry and the Environment. We thank the IUPAC officers responsible, especially the executive director, Dr John Jost, for their support and assistance. We also thank the International Council for Science (ICSU) for financial support of the work of the Commission. This enabled us to organise the discussion meeting of the full team of chapter authors (in Diibendorf, Switzerland, 2001) which formed such an essential step in the preparation and harmonisation of the various chapters of this book. 

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