Other Examples

In Other classes of organic halides, for example perfluoroalkyl and vinyl halides, the distinction between stepwise and concerted electron-transfer-bond-breaking upon reduction by outer sphere heterogeneous and/or homogeneous electron donors is less unambiguous than in the case of aryl and alkyl halides. As discussed in Section 3, they also present the interest of being active substrates in Sg l reactions. 

Similar questions arise for other polyhaloalkanes such as CCI4, CBr and CCljBr. Their reduction by two bulky coordination compounds (a polyoxo-metallate and a sepulchrate ) reputed to function as outer sphere electron donors have been recently investigated (Eberson and Ekstrom 1988a,b) as well as the reduction of CCI4 by aromatic anion radicals (Eberson et al., 

From the rate data thus obtained it is difficult to conclude whether the reaction goes through the intermediacy of the polyhalogenoalkane anion radical or rather follows a concerted pathway. The fact that the anion radicals have been detected under quite different medium and driving force conditions (Brickenstein and Khairutdinov, 1985 Mishra and Symons, 1973) does not provide unequivocal evidence for the stepwise pathway, as discussed earlier. Some evidence in favour of the latter mechanism was. 

For the reduction of CCI4 by electrochemically generated aromatic anion radicals in DMF (Eberson et al., 1989), the kinetics were treated according to a reaction scheme in which CCl, appears as an intermediate, but no strong evidence was offered that they would not fit a concerted pathway as well. As discussed on pp. 32, 33, it is indeed not possible to distinguish between the two pathways in such types of experiment when, in the stepwise pathway, the cleavage reaction is so fast that the electron-transfer step would be rate determining, a situation likely to be met in the present case. 

The reduction of aryl-substituted vinyl halides by electrochemically generated aromatic anion radicals has also been investigated in DMF (Gatti et al., 1987). Counter-diffusion behaviour at low driving forces (pp. 34, 35) does not appear as clearly as in the case of aryl halides (Fig. 11). However, analysis of the log k vs E° plot according to a quadratic activation-driving force relationship gave standard potential and intrinsic barrier values that 

As further examples, we consider isomers of the chlorinated dibenzodioxins. The molecule is shown in Fig. 12.3. It has the symmetries as given in Table 12.2. We obtain the generating function for the entire number to isomers in Eq. (12.9). 

If we set h and x equal to 1, then we obtain 76 isomers. In the literature, the number to chlorinated isomers, often also referred to as congeners, is given as 75. That comes along because here we also take into account completely nonchlorinated isomers. Written out, the generating function reads as 

If we put h and x equal to 1, then we find the number of isomers as 136. Written out, the generating function reads 

The literature offers many more examples of electron transfer induced rearrangements of compounds containing three-membered rings. In general it is not known whether the rearrangement occurs at the radical anion or dianion stage, as is the case in the above-mentioned examples. 

Reaction of dibenzonorcaradiene 53 with lithium, sodium or potassium naphthal-enide followed by quenching with water led to 9-methyl-phenanthrene 54 (16-24%), 9-methyl-9,10-dihydrophenanthrene 55 (33-43%) and 6,7-dihydro-5-H-dibenzo-[a,c]cycloheptane 56 (23-34%) 52). 

Preferential cleavage of bond a in the presumed radical anion 57 is caused by the familiar stereoelectronic effect (see Sect. 2.3). The formation of 56 via cleavage of bond b, however, is not established. 

Electron transfer on 58 gives the rearranged 59 60, in contrast, gives the closed radical anion 6153). 

Reduction of cw-bicyclo[6.1.0]nona-2,4,6-triene cis-62 proceeds through the nine electron homoaromatic radical anion 63 to give the monohomocyclooctatetraene 

Section 4.3 on Process Development includes additional examples of opportunities for process minimization or intensification, including  

Truxene and truxone were the first members of what is now a large family of tris-annulated benzenes that have been synthesized by aldol trimerizations of cyclic ketones during the past 125 years. Table 1 provides some additional representative examples [6, 10, 21-29]. 

This list is undoubtedly incomplete however, some general observations can be made on the basis of just these examples. First, it should be noted that good yields of cyclic trimers 

It is equally noteworthy that both aliphatic and aromatic ketones undergo the aldol trimerization reaction. 

For all but the most symmetrical trimers, two distinct cyclocondensations can be identified as potential synthetic routes starting from two isomeric ketones (e.g., 13 = 15). 

Finally, as one might expect, aldol trimerizations that lead to sterically crowded products generally fail or give the trimer only in modest yield (e.g., 21 and 27, the quoted yields for which represent optimized values). The high degree of regioselectivity seen in the trimeri- 

CMP used to expose chips between bonding layers in a 3D fabrication scheme (from Ref. ). 

FIGURE 20.16 In a second 3D fabrication scheme, CMP is used to smooth the wafer surface after lateral epitaxial growth. After a first layer of transistor fabrication, a second layer of device quality Si is grown from seed holes in Si02 down to the original wafer surface. This process allows for transistor fabrication on multiple levels of the wafer surface (from Ref. 15). 

End points may also be detected using so-called ion-selective electrodes. Such titrations are called 

HISTORY OF THEORETICAL CHEMISTRY AT THE NATIONAL RESEARCH COUNCIL OF CANADA 

Although the research of Gerhard Herzberg and his colleagues at the National Research Council of Canada needs no introduction to computational and theoretical chemists, the emergence of theoretical and computational chemistry at the NRC is a relatively recent development. 

The changing political climate of the early 1980s, which ran against pure science and especially theory, coincided with the need of theorists to 

A rigorous modelling of thermal broadening is — in practice — quite cumbersome and tedious. Let us consider a general asymmetric top molecule such as H2O, for example. Each total angular momentum state, specified by the quantum number J, splits into (2 J + 1) nondegenerate substates with energies E 0f (K = 1. 2J + 1). Every one of these (2J + 1) rotational states corresponds to a different type of rotational motion and is described by a distinct rotational wavefunction (see Section 11.3). 

Cases for which both parent rotation as well as translational-rotational coupling have a more balanced weight are certainly more difficult to analyze. 

The high-resolution solid state 13C NMR spectra of polymorphs of naphthazarin (5,8-dihydroxy-1,4-napthoquinone) and methyl derivatives have been rationalised in terms of hydrogen bonding effects [143]. There are three polymorphs (denoted A, B and C) of naphthazarin, in each of which, at room temperature, the molecules occupy crystallographic inversion centres. As shown below, there is a proton transfer reaction between the two forms la and lb. In solution, this proton transfer is fast on the H and 13C NMR timescales. 

we consider the application of 13C NMR to probe materials containing N-H---N hydrogen bonds. In the crystal structure of campho[2,3-c]pyrazole 

The complex hydrogen bonding arrangement in the biomedically important molecule bilirubin IXa, an unsymmetrically substituted tetrapyrrole dicar-boxylic acid (shown below), and its dimethyl ester have been probed by using H DQ MAS NMR [23]. 

Finally, the N- -H distance in the hydrogen bonding arrangement adopted by a pair of methyl-substituted benzoxazine dimers has been determined by solid state NMR to be 1.94 A [148]. 

The results indicate that the proton is shared between the nitrogen and oxygen atoms, with a preference for O-H rather than N-H character. Further advanced solid state NMR methods were used to measure the N -H distance via the N - - H dipolar coupling. 

The employment of diphenylphosphinopropanoic acid as a building block in the supramolecular assembly of a cyclometalated platinum(II) polymer 49 directed by -stacking and hydrogen-bonding interactions has been described [ 16g]. 

The orthometalated Pt(II) complexes [Pt(phpy)2] and [Pt(thpy)2] (Hphpy=2-phenylpyridine, Hthpy=2-(2 -thienyl)pyridine) are photosensitive in several organic solvents, giving rise to oxidative addition reactions 

Cyclopalladation of 4 -(functionalized)-6 -phenyl-2)2,-bipyridine ligands (HL) afforded several new [PdLCl] complexes liquid crystalline complex 50 exhibits thermotropic nematic mesomorphism, which represents the first example of an organometallic mesogen with a terdentate o-C deprotonated ligand. Complex 50 is photoluminescent at 77 K [48]. Other researchers have reported the applications of orf/m-platinated or -palladated complexes bearing azobenzene or imine ligands as liquid crystalline materials [49]. 

3 Filling composite structures centrically (cut, fill and press process, Eisele ). 

2 Recycling waste bonded by means of phenolic-resin 

There is a German supplier to the automotive industry where production waste of moulded parts of cotton and phenol resin is re-used. The waste is cut and used as a centric ply in between two layers of nonwoven. The result is a mat structure which, directly after it is achieved, is thermally bonded (Fig. 9.3). 

Concerning the cleaning of industrial sewage, both national and international standards are high. A nonwoven of reclaimed fibres is good value and functional, and can substitute for costly synthetic fibre materials. The nonwoven can be used to adsorb heavy metal ions (Pb(+2) ions, Cu(+2) ions, Zn(+2) ions), acid dyes (C.l. acid red 27, C.l. acid red 88) and oils (basic oil SN 150, diesel, crude oil). This requires a particular kind of surface modification treatment. For example, the woollen nonwoven is treated with biopolymer chitosan and low temperature plasma to ensure that heavy metals are better adsorbed. Investigations have shown that woollen reclaimed fibres are especially well suited to adsorb Pb (+2) ions. The adsorption of copper and zinc is also clearly improved through chitosan and plasma treatment. 

Woollen nonwovens are useful in absorbing oil films on water surfaces.  

Solvent p of C2H4 in mm Hg Bunsen coefficient a Gas solubility, mole/liter at 1 atm  

From a scrutiny of Fig. 13, it could be predicted that the Ncjh vs pcjHe plot for 25 C for the whole range of NcjHe values would probably be concave upward just on the right of the R-line. Rodriques, McCaffrey, and Kohn (1968) have recorded data for t°C from 0 to 100 C and paiu up to 22 atm for 0°C and 52 atm for 75°C. Their NcjHe vs PcaHe plots for octane at 0, 25, 40, 50, 75, and 100°C are concave upward. In Fig. 139,1 have given the JCcjHe plot for 25°C against my R-line. 

The vapor pressures of hydrocarbons have special significance in the petroleum industry, and it is relevant to effect a link with this aspect by the brief citation of the following. 

Hoffman, Welker, Felt, and Weber (1962) pointed out that satisfactory values for the hypothetical vapor pressure may be obtained by extrapolating the vapor pressure curve into the supercritical region. Methane, ethane, propane, n-pentane, and n-octane were examined. 

In a paper by Bradford and Thodos (1966), 4 of the 16 references are to Hildebrand et ai, one to Chao and Seader, one to Prausnitz and Edmister, one to Frost and Kalkwarf, and the remainder to Thodos and his colleagues. The solubility parameter 5 is a temperature-dependent quantity, and when we are dealing with the difference between the 5a and 5s values, we are presented with differential effects. It was pointed out by the authors that the 5 value at 25°C has been assumed to be the same for other temperatures for utility purposes and represents a fictitious or empirical value. Data for n-hydrocarbons from methane to dodecane and for ethylene, propylene, 1,3-butadiene, cyclohexane, and benzene were given. 

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Appraisal activity should be based upon the information required. The first step is therefore to determine what uncertainties appraisal is trying to reduce, and then what information is required to tie down those uncertainties. For example, if fluid contacts are a major source of uncertainty, drilling wells to penetrate the contacts is an appropriate tool seismic data or well testing may not be. Other examples of appraisal tools are ... 

Other examples of government and military applications of laser-based profilometry include the evaluation of rocket thruster nozzles to locate and measure flame erosion remote inspection of hypervelocity test track and the measurement of sludge deposits on tube internal surfaces. 

Qualitative examples abound. Perfect crystals of sodium carbonate, sulfate, or phosphate may be kept for years without efflorescing, although if scratched, they begin to do so immediately. Too strongly heated or burned lime or plaster of Paris takes up the first traces of water only with difficulty. Reactions of this type tend to be autocat-alytic. The initial rate is slow, due to the absence of the necessary linear interface, but the rate accelerates as more and more product is formed. See Refs. 147-153 for other examples. Ruckenstein [154] has discussed a kinetic model based on nucleation theory. There is certainly evidence that patches of product may be present, as in the oxidation of Mo(lOO) surfaces [155], and that surface defects are important [156]. There may be catalysis thus reaction VII-27 is catalyzed by water vapor [157]. A topotactic reaction is one where the product or products retain the external crystalline shape of the reactant crystal [158]. More often, however, there is a complicated morphology with pitting, cracking, and pore formation, as with calcium carbonate [159]. 

Many solids have foreign atoms or molecular groupings on their surfaces that are so tightly held that they do not really enter into adsorption-desorption equilibrium and so can be regarded as part of the surface structure. The partial surface oxidation of carbon blacks has been mentioned as having an important influence on their adsorptive behavior (Section X-3A) depending on conditions, the oxidized surface may be acidic or basic (see Ref. 61), and the surface pattern of the carbon rings may be affected [62]. As one other example, the chemical nature of the acidic sites of silica-alumina catalysts has been a subject of much discussion. The main question has been whether the sites represented Brpnsted (proton donor) or Lewis (electron-acceptor) acids. Hall... 

See Refs. 80 and 81 for other examples. Surface-enhanced Raman spectroscopy is discussed in Section XVI-4C. 

Two other examples will sufhce. Methane physisorbs on NaCl(lOO) and an early study showed that the symmetrical, IR-inactive v mode could now be observed [97]. In more recent work, polarized FTIR rehection spectroscopy was used to determine that on being adsorbed, the three-fold degeneracies of the vs and v modes were partially removed [98]. This hnding allowed consideration of possible adsorbate-adsorbent geometries one was that of a tripod with three of the methane hydrogens on the surface. The systems were at between 4 and 40 K so that the equilibrium pressure was very low, about 10 atm. 

Other examples of order-disorder second-order transitions are found in the alloys CuPd and Fe Al. Flowever, not all ordered alloys pass tlirough second-order transitions frequently the partially ordered structure changes to a disordered structure at a first-order transition. 

There are many other examples of second-order transitions involving critical phenomena. Only a few can be mentioned here. 

Other examples are iron pentacarbonyl, Fe(CO)s, and chromium hexacarbonyl, Cr(CO)(j, which have trigonal bipyramidal and octahedral configurations respectively. 

Other examples of water as an apparent catalyst are (a) carbon monoxide will not bum in oxygen unless a trace of water is present. 

There have been plenty of other examples of similar developments in the area of molecular structure input/output, especially during the third quarter of the 20th... 

Representation of such a system by a connection tabic having bonds between the iron atom and the five carbon atoms of either one of the two cyclopentadienyl rings is totally inadequate. A few other examples of structures that can no longer be adequately described by a standard connection table are given in the Section 2.G.2. 

Many other examples of the Claisen Condensation will be found in textbooks of theoretical organic chemistry. 

For other examples of the synthetic application of ethyl acetoacetate, see below and pp. 293 295. 

The melting points of some typical substituted aromatic amides are collected in Table IV,192. Other examples will be found in the appropriate columns of Tables IV,100A and B Primary and Secondary Aromatic Amines) and of Table IV,175 (Aromatic Carboxylic Acids). 

There are many other examples of interrelationship. Symmetry, for example, is of fundamental importance in the sciences and arts alike. It plays a key role in our understanding of the atomic world as well as the cosmos. The handedness of molecules, with nature selecting one... 

Several of the naturally occurring indoles also have clinical importance. The dimeric vinca alkaloid vincristine and closely related compounds were among the first of the anti-mitotic class of chemotherapeutic agents for cancer[14]. The mitomycins[15] and derivatives of ellipticine[16] are other examples of compounds having anti-tumour activity. Reserpine, while not now a major drug, was one of the first compounds to show beneficial effects in treatment of mental disorders[17]... 

The Gassman method has proven to be adaptable to complex structures, such as the intermediate 7.20B used in the synthesis of the indole diterpenes paspalicine and pasalinine[5]. Table 7.5 gives some other examples. 

The exocyclic nitrogen is reactive even when already substituted 2-anilinothiazole (110) is acetylated by acetic anhydride (120). other examples of this reactivity are given in the tables (Section VII). 

The reaction of 2-amino-5-nitrothiazole with (3-chloroethyl isocyanate gives the corresponding thiazolyl urea (137) (Scheme 90) (298). Other examples are given in Section V.l.B, where the preparation of thiazolyl-thioureas is discussed,... 

An other example is the oxidation of 4-(hydroxymethyl)thiazole with a mixture of nitric and sulfuric acids at -5°C (24, 27). 

Other examples, concerning the water-silica system, are referred to later in the Chapter. 

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