Indirect evidence

It should be noted that all of the above complexes (except N4) either contain heavy atoms such as Br and I or are formed from reactants containing several double bonds. It has also been found that all of the isomeric pentene ions and cyclopentene ions form dimeric ions as one of the products of reactions with corresponding neutral molecules in the pressure range of 1—10 microns [132]. Recently, saturated hydrocarbons, ethane and propane, have also been found to form dimeric ions under certain conditions (see Sections 6.1.2 and 6.1.3). 

This type of complex has a lifetime which is too short to be detected in mass spectrometry ( 10 sec) but is long enough for statistical distribution of the excess energy among degrees of freedom to occur ( 10 sec), and is called a statistical complex.  

Another kind of indirect evidence for complex formation is found in the study of collision-induced dissociation of D3 by Leventhal and Friedman [135]. They found in tandem mass spectrometer experiments that the energy threshold (CM) of the reaction D3 -hX- D + D2 + Xis independent of X, where X = He, He, and Ne. This means the whole of the energy available to drive the reaction (= CM energy) is always used. Some sort of XD3 complex would be necessary for this complete energy transfer. 

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It is obvious that the reaction is accelerated markedly by water. However, for the first time, the Diels-Alder reaction is not fastest in water, but in 2,2,2-trifiuoroethanol (TFE). This might well be a result of the high Bronsted acidity of this solvent. Indirect evidence comes from the pH-dependence of the rate of reaction in water (Figure 2.1). Protonation of the pyridyl nitrogen obviously accelerates the reaction. 

Peroxosilicates. No sohd peroxosiUcates are known. There is some indirect evidence based on catalytic studies for the existence of peroxosihcates in solution (32,33), but nmr spectra of aqueous solutions of siUcates mixed with hydrogen peroxide give no evidence for peroxo species (34). A peroxohydrate of sodium siUcate, Na SiO 3H202, is well estabhshed (35—37) but has found no appHcation. 

The 1,2-bond is homolytically cleaved by both thermolytic and photolytic means to generate a biradical (17) which in the absence of reactive groups generally forms a 2//-azirine (79AHC(25)147). No direct evidence for the biradical has been presented, but indirect evidence points to such a species. Acylpyrazines have in some instances been isolated, and these would arise by dimerization of the biradical (70JCS(C)1825, 7UCS(C)2644). 

Doubt (75ZN(B)822) has been cast on a number of claims for the formation of 2-azetin-4-ones from cycloaddition of activated isocyanates to acetylenes (70TL119). The simple 2-azetin-4-one (246) was not isolated or even detected directly at -50 °C in the photofragmentation of compound (245), but indirect evidence for its formation was the isolation of adducts (248 X = MeO, MeNH) in the presence of methanol or methylamine (75TL1335). The most convincing evidence for an isolable 2-azetin-4-one involves treatment of the... 

The determination of the degree of dissociation of cotarnine ° and the good agreement with the values derived from measurements of electrical conductivity with those from the spectrophotometric methods is indirect evidence that no significant part of the undissociated cotarnine is in the amino-aldehyde form. In the conductance calculation, the undissociated part was neglected. If this included a significant amount of amino-aldehyde (i.e., a secondary base), there would be a noticeable discrepancy in the degree of dissociation obtained by the two methods. 

No 1 -hydroxytryptamine or -tryptophan alkaloid that lacks a stabilizing group on the indole nucleus has been reported yet. However, isolation of37,38a, 38b, HUN-7293 (293) (96MI69), and apicidin (301) (96TL8077) offers indirect evidence for the existence of 1-hydroxytryptamines and/or 1-hydroxytryptophans in living organisms. We believe their isolation will be reported in the near future. 

Finally, increases in the intensity or variability of weather are considered another form of indirect evidence reflecting whether Earth is currently undergoing human-driven climate change. Predictions of increased incidence of extreme temperatures, tornadoes, thunderstorms, dust storms and fire-promoting weather have been drawn from basic global climate change theoiy. However, evidence has not so far borne out these predictions on a global scale. The IPCC concludes ... 

Hydrogen has a very low solubility in the iron lattice, which makes direct observation of the location of the hydrogen atom in the lattice very difficult. The hydrogen definitely occupies an interstitial site in the bcc iron lattice. Two such sites are normally associated with interstitial solutes in bcc structures, the tetrahedral and the octahedral sites (see Fig. 8.39). Indirect evidence suggests that hydrogen occupies the tetrahedral site. 

A substantial amount of indirect evidence supports the contention that the induction of apoptosis in tumor cells is critical to successful therapy. Cancer therapy might therefore be viewed as an attempt to induce apoptosis in a population of cells that have undergone selection for apoptotic defects. If correct, this hypothesis would suggest why cancer therapy is in many cases unsuccessful. However, recent studies indicate that this fundamental problem can be circumvented. Progress in the identification of molecules key to the cell death pathways has led to a growing understanding of how apoptosis occurs [3]. It has become clear that pathways to apoptosis are numerous and often interconnected. A solution to the clinical problem of therapeutic resistance, then, may lie in the fact that there appears to be multiple ways that a cell death program can be implemented. 

It is usually assumed that propagation rate constants in homopolymerization ( p) arc independent of chain length and, for longer chains (length >20), there is experimental evidence to support this assumption.356 6 However, there is now a body of indirect evidence to suggest that the rate constants for the first few propagation steps p(l), kp(2), etc. can be substantially different from (overall) (refer Scheme 4.45). The effect can be seen as a special ease of a penultimate unit effect (Section 7.3,1.2). Evidence comes from a number of sources, for example ... 

A reaction interface is the zone immediately adjoining the surface of contact between reactant and product and within which bond redistributions occur. Prevailing conditions are different from those characteristic of the reactant bulk as demonstrated by the enhanced reactivity, usually attributed to local strain, catalysis by products, etc. Considerable difficulties attend investigation of the mechanisms of interface reactions because this thin zone is interposed between two relatively much larger particles. Accordingly, many proposed reaction models are necessarily based on indirect evidence. Without wishing to appear unnecessarily pessimistic, we consider it appropriate to mention here some of the problems inherent in the provision of detailed mechanisms for solid phase rate processes. These difficulties are not always apparent in interpretations and proposals appearing in the literature. 

All of the information obtained in this research area depends upon indirect evidence through the use of nonisotopic carriers or normalized data in the form of ratios. These are subject to error but the trends and insights that have been obtained are very useful to the description of the behavior of plutonium in the environment. Better thermodynamic data in the range of environmental concentrations would be helpful in further quantification of chemical species, as would phenomenalogical descriptions of the behavior of plutonium in reasonably good models of the environment. 

Back reflection of translational and rotational velocity is rather reasonable, but the extremum in the free-path time distribution was never found when collisional statistics were checked by computer simulation. Even in the hard-sphere solid the statistics only deviate slightly from Pois-sonian at the highest free-paths [74] in contrast to the prediction of free volume theories. The collisional statistics have recently been investigated by MD simulation of 108 hard spheres at reduced density n/ o = 0.65 (where no is the density of closest packing) [75], The obtained ratio t2/l2 = 2.07 was very close to 2, which is indirect evidence for uniform... 

The structure of the adducts obtained (addition resulted from homolysis of C-Br bond) is an indirect evidence for radical character of the process. Ionic addition of haloforms is known to occur at C-H bond (ref. 11), this leads to adducts with CX3 group. The highest yield of the adduct with bromoform was obtained for... 

A systematic difference is found, supported by indirect evidence that from experience precludes any explanation other than effect observed. This case does not necessarily call for a statistical evaluation, but an example will nonetheless be provided in the elemental analysis of organic chemicals (CHN analysis) reproducibilities of 0.2 to 0.3% are routine (for a mean of 38.4 wt-% C, for example, this gives a true value within the bounds 38.0. .. 38.8 wt-% for 95% probability). It is not out of the ordinary that traces of the solvent used in the... 

Health effects in humans and animals provide indirect evidence of absorption of endosulfan following oral, inhalation, and dermal exposures. Endosulfan and metabolites have been detected in tissues of humans and animals following various exposures to endosulfan, providing qualitative evidence that... 

Indirect evidence indicates that dermal absorption occurs in animals. Calves dusted with a 4% dust formulation of endosulfan had neurological symptoms (tremors, twitching, convulsions) and died within a day after exposure (Nicholson and Cooper 1977). Neurological effects have also been reported in preclipped rabbits and rats after repeated application of endosulfan to the skin (Dikshith et al. 1988 Gupta and Chandra 1975). Dikshith et al. (1988) reported levels of a-, [3-, and total endosulfan in liver, kidney, brain, testes, fatty tissue, and blood 30 days after dermal application of endosulfan. 

An intermediate could be isolated in the case of aniline and Co(DMG)2 and indirect evidence suggested the presence of a PhNHCH2—Co bond (164,165). 

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