From the Literature

A small smorgasbord of published papers will be discussed here, to show how some of the things that we have seen in previous chapters have appeared in the literature. The four topics of this section (oxirene, nitrogen pentafluoride, pyramidane and nitrogen polymers), and several others, are addressed in more detail in another book [1], 

Let s start with what looks like a simple problem what can computational chemistry tell us about oxirene (oxacyclopropene, Fig. 9.1 the oxirene literature till 1983 has been reviewed [2]). Labelling one of the carbons of a diazo ketone (R-C(N2)-CO-R) can lead to a ketene with scrambled labelling. After excluding the possibility of scrambling in the diazo compound, this indicates that an oxirene 

9 Selected Literature Highlights, Books, Websites, Software and Hardware 

A detailed computational study of the ozonolysis of ethyne skirted the question of the involvement of oxirene by saying that it will easily revert to [the carbene] therefore, the oxirene route was not further investigated in this work [7]. 

In recent work (2008) ultrafast photolysis of a potential diazo ketone precursor of p-biphenylmethyloxirene failed to detect the oxirene, the UV absorption of which could, however, have been hidden by another band [8], and in a combined experimental/computational (ab initio and molecular dynamics with DFT) study, flash thermolysis of a formal Diels-Alder adduct was interpreted as affording acetylmethyloxirene and benzene [9]. 

A small smorgasbord of published papers will be discussed here, to show how some of the things that we have seen in previous chapters have appeared in the literature. 

Nitrogen pentafluoride represents an interesting contrast to oxirene. Oxirene is, on paper, a reasonable molecule there is no obvious reason why, however unstable it might be because of antiaromaticity [4] or strain, it should not be able to exist. On the other hand, NFs defies the hallowed octet rule why should it be more reasonable than, say, CHfi Yet a comprehensive computational study of this molecule left tittle doubt that it is a (relative) minimum on its potential energy surface [5]. The full armamentarium of post-HF methods, CASSDF, MRCl, CCSDT, CCSD(T), MP2 (section 5.4) and DFT (chapter 7) was employed here, and all agreed that Dan (section 2.6) NF5 is a minimum. 

If oxirene should exist and NF5 should not, what are we to make of pyramidane (Fig. 8.3) This molecule contradicts the traditional paradigm [6] of tetracoordinate carbon having its bonds tetrahedrally directed the four bonds of the apical carbon point toward the base of a pyramid. Part of the calculated [7] potential energy surface of pyramidane is shown in Fig. 8.3. To improve the accuracy of the relative energies, the MP2 geometries were subjected to single-point calculations (section 

N) of these molecules have been investigated computa- 

There has in recent years been considerable interest in the possibility of making allotropes of nitrogen with more than two atoms per molecule. Curiously, almost all (the Ns cation has been made [9, 10]) the work reported has been computational rather than experimental. These compounds are interesting because to any chemist with imagination the idea of a form of pure nitrogen that is not a gas at room temperature is fascinating, and because any such compound would be thermodynamically very unstable with respect to decomposition to dinitrogen. 

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The correlations were generated by first choosing from the literature the best sets of vapor-pressure data for each fluid. 

I This formula shows that if quantitative analysis in the infrared is to be possible, it is necessary to know the coefficients a( i ), therefore, either to have the pure substance, or to be able to obtain them from the literature... 

A seemingly more stringent test would be to determine whether the ratios of areas for various solids as obtained by means of a given isotherm equation are independent of the nature of the adsorbate. The data summarized in Table XVII-3 were selected from the literature mainly because each author had obtained areas for two or more solids using two or more adsorbates. It is seen... 

While the stick plot examples already presented show net and multiplet effects as separate phenomena, the two can be observed in the same spectrum or even in the same NMR signal. The following examples from the literature will illustrate real life uses of CIDNP and demonstrate the variety of structural, mechanistic, and spin physics questions which CIDNP can answer. 

A relatively small training set of 744 NMR chemical shifts for protons from 1 20 molecular structures was collected from the literature. This set was designed to cover as many situations of protons in organic structures as possible. Only data from spectra obtained in CDCl, were considered. The collection was restricted to CH protons and to compounds containing the elements C, H, N, 0, S, F, Cl, Br. or I. 

The half-lives for these four compounds taken from the literature allowed the estimation of the Four reaction rates necessai to model their degradation [18], As a first approximation, the rate of hydrolysis of the C-Cl bond of all Four, -triazine compounds was assumed to be the same and to be 5.0 x 10 s on the basis of literature precedence. This approximation seems reasonable as the four structures differ only in the alkyl groups at a site quite remote from the C-CI bond. Furthermore, among the Four reaction steps hydrolysis is the slowest anyway. 

The same considerations are fundamental in the analysis of more complex molecules, which we shall discuss in the following chapter, with the exception that in item (ii) the special substructures are generally related to more complex, non-commercial precursors, which are known from the literature. 

At the outset, we were faced with the difficult decision whether to use the Angstrom unit or the nanometre for the dimensions of molecules. After careful consideration, we have come down firmly in favour of the Angstrom and we believe that this decision will meet with the approval of the majority of our readers. When quoting graphs and tables of data from the literature, we have retained the original units (kcal, Torr, C, tonin, etc.) in the belief that it is more reasonable to state the data in the form used by the original author—except where comparisons are being made between results presented in different units. 

We therefore felt it timely to attempt a critical exposition and assessment of the common methods for the evaluation of the surface area and pore size distribution of solids from adsorption measurements. Our main concern has therefore been with the use of adsorption data for these purposes rather than with adsorption per se and it is for this reason that our treatment of theoretical matters, whilst sufficiently detailed to bring out the nature of the assumptions underlying the various methods, is not exhaustive we have not set out to write a text-book or a treatise on adsorption, and our choice of material from the literature has been dictated solely by its seeming suitability for the explanation or illustration of the topic under discussion. 

Problems adapted from the literature. Many of the in-chapter examples and end-of-chapter problems are based on data from the analytical literature, providing students with practical examples of current research in analytical chemistry. 

Several comments about the toxicity of pharmaceutical, agrochemical and azo dye pyrazoles have been made previously in Section 4.04.4.1. Some LDso values from the literature are shown in Table 41 (B-76MI40404). 

Plasticization and Other Time Effects Most data from the literature, including those presented above are taken from experiments where one gas at a time is tested, with Ot calculated as a ratio of the two permeabihties. If either gas permeates because of a high-sorption coefficient rather than a high diffusivity, there may be an increase in the permeabihty of all gases in contact with the membrane. Thus, the Ot actually found in a real separation may be much lower than that calculated by the simple ratio of permeabilities. The data in the hterature do not rehably include the plasticization effect. If present, it results in the sometimes slow relaxation of polymer structure giving a rise in permeabihty and a dramatic dechne in selectivity. 

The laboratory studies utilized small-scale (1-5-L) reactors. These are satisfactoiy because the reaction rates observed are independent of reac tor size. Several reac tors are operated in parallel on the waste, each at a different BSRT When steady state is reached after several weeks, data on the biomass level (X) in the system and the untreated waste level in the effluent (usually in terms of BOD or COD) are collected. These data can be plotted for equation forms that will yield linear plots on rec tangular coordinates. From the intercepts and the slope or the hnes, it is possible to determine values of the four pseudo constants. Table 25-42 presents some available data from the literature on these pseudo constants. Figure 25-53 illustrates the procedure for their determination from the laboratory studies discussed previously. 

Drawing inferences from the literature available on the subject (see the further reading at the end of the chapter), based on laboratory tests, practical experience and the field data available, deratings for different configurations are shown in Table 28.7 which should be sufficient to account for the likely proximity effects... 

Ionisation constants of ionisable compounds are give as pK values (published from the literature) and refer to the pKa values at room temperature ( 15 C to 25 C). The values at other temperatures are given as superscripts, e.g. pK for 25 C. Estimated values are entered as pKgjt (see Chapter 1, p. 7 for further information). 

By its nature, the present treatment is not exhaustive, nor do we claim that any of the methods taken from the literature are the best possible. Nevertheless, we feel that the information contained in this book is likely to be helpful to a wide range of laboratory workers, including physical and inorganic chemists, research students, biochemists, and biologists. We hope that it will also be of use, although perhaps to only a limited extent, to experienced organic chemists. 

To facilitate the use of methanol synthesis in examples, the UCKRON and VEKRON test problems (Berty et al 1989, Arva and Szeifert 1989) will be applied. In the development of the test problem, methanol synthesis served as an example. The physical properties, thermodynamic conditions, technology and average rate of reaction were taken from the literature of methanol synthesis. For the kinetics, however, an artificial mechanism was created that had a known and rigorous mathematical solution. It was fundamentally important to create a fixed basis of comparison with various approximate mathematical models for kinetics. These were derived by simulated experiments from the test problems with added random error. See Appendix A and B, Berty et al, 1989. 

All cost estimates are based on historical costs accumulated from previous projects. This history can be in-house, from vendors, or from the literature. The accuracy of an estimate depends on how completely the project is defined, and on how well the costs from previous projects have been analyzed and correlated. If your company does not have good (or any) past project records, the literature abounds with correlations of cost data, as discussed later. However, this data must be used very carefully. 

Next we will make use of mixture data from the literature in Figures 1 and 2. 

Data Source. The correlation constants were determined from a least-squares fit of data from the literature.-- - In most cases, average deviations between calculated and reported data were less than 0.6kjoules/g-mol. 

Some collected values for RTI taken from the literature are given in Table 9.1. (These are given for guidance only and should not be taken to imply official UL ratings.)... 

The hazards and safety preeautions for seleeted eommon eompressed gases are diseussed below to illustrate the general approaeh. More details should be sought from suppliers. Some methods for their preparation in situ are noted full experimental details must be obtained from the literature. 

The term "hydrophobic interaction" unfortunately implies some form of molecular repulsion, which, outside the van der Waals radii of a molecule, is quite impossible. The term "hydrophobic force" literally means "fear of water" force. The term hydrophobic has been introduced as an alternative to dispersive but means the same. It is not clear from the literature how the word hydrophobic originated, but it may have been provoked by the immiscibility of a dispersive solvent such as n-heptane with a very polar solvent such as water. 

There was some argument in the literature over the relative merits and demerits of the JKR and the DMT theories [23-26], but the controversy has now been satisfactorily resolved. A critical comparison of the JKR and DMT theories can be obtained from the literature [23-30]. According to Tabor [23], JKR theory is valid when the dimensionless parameter given by Eq. 25 exceeds a value of about five. 

A principal aim of the discussion thus far has been to set out a theoretical framework within which it is possible to rationalise the effects of surface roughness on adhesion. It may be useful to summarise this framework before examining practical examples taken from the literature. 

Equilibrium Considerations - Most of the adsorption data available from the literature are equilibrium data. Equilibrium data are useful in determining the maximum adsorbent loading which can be obtained for a specific adsorbate-adsorbent system under given operating conditions. However, equilibrium data by themselves are insufficient for design of an adsorption system. Overall mass transfer rate data are also necessary. 

Table 1 provides states the temperature range over which the correlation constants are reported from the literature. Estimates from this expression using the constants in Table 1 are generally accurate and typically provide agreement to well within + 1% compared to experimentally measured thermal conductivities. 

The following analysis enables one to calculate the diameter of a pipeline transporting any compressible fluid. The required inputs are volumetric flow rate, the specific gravity of the gas relative to air, flow conditions, compressibility factor Z where Z is defined by nZRT = PV, the pressure at the point of origin and the destination, the pipe length, and pipe constants such as effective roughness. The working equations have been obtained from the literature. Since the friction factor... 

Step 2 Select the appropriate flame emissivity factor F, based on flare gas composition. For ignited vents, lower values are recommended. The following are emissivity values reported from the literature ... 

The objeetive of the following model is to investigate the extent to whieh Computational Fluid Mixing (CFM) models ean be used as a tool in the design of industrial reaetors. The eommereially available program. Fluent , is used to ealeulate the flow pattern and the transport and reaetion of ehemieal speeies in stirred tanks. The blend time predietions are eompared with a literature eonelation for blend time. The produet distribution for a pair of eompeting ehemieal reaetions is eompared with experimental data from the literature. 

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