Experimental Proof

A year before that, first experimental results had already suggested the existence of certain carbon clusters. In experiments on laser-evaporation of graphite, signals attributable to the clusters of 30 to 190 carbon atoms had been detected in the time-of-flight mass spectmm. Most peculiar was the fact that only even numbers of atoms had been observed. StiU for the time being, the clusters structure had not been elucidated. 

It was only in 1990 when the groups of W. Kratschmer and D. R. Huffman succeeded in isolating macroscopic amounts of the most abundant fuUerene C o by the arc evaporation of graphite or by resistance heating of graphite electrodes, respectively. In fact, their initial intention, too had been to produce in the laboratory substances that exist in interstellar dust, but at suitable conditions, their IR-spectra exhibited four sharp, characteristic signals that related to those predicted for the Ceo-molecule. Later on, C70 and the higher fullerenes were also obtained. 

The first description of fuUerenes containing one or more atoms within the cage followed soon after detection of the fundamental structure. These so-called endo-hedral fuUerenes played a crucial part in the isolation of higher fuUerenes. 

It has long been recognized that foodstuffs other than lipids can be a source of body fat. The wide usage of corn as a fattening agent for hogs 

We have no experimental evidence on the exact intermediary changes which occur in the complex transformations necessary to convert sugar into fat. The quantities of any such intermediates that may be present in the tissues at any one time are probably so small as to make then-detection a relatively hopeless task. Lusk calculates that a 13.5 kg. hog can synthesize a maximum of 2 mg. of fat per second. If such transformations are generalized throughout the organism, this rate would involve a concentration at any instant of only 0.15 fig. per g. of tissue. 

Although there is little direct evidence that acetaldehyde may serve as the important intermediate, it has been reported as a component of urine. Such a scheme could explain the universal appearance of even-chain fatty acids in the tissues as well as does the suggestion that they originate by a series of d-oxidations from longer-chain acids. 

An especially cogent argument for the acetaldehyde theory is the fact that considerable amounts of pyruvic acid accumulate in the organism 

Transformation of Fatty Adds with Odd-numbered Carbon Chains to Carbohydrate 

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When Davisson and Germer reported in 1927 that the elastic scattering of low-energy electrons from well ordered surfaces leads to diffraction spots similar to those observed in X-ray diffraction [2.238-2.240], this was the first experimental proof of the wave nature of electrons. A few years before, in 1923, De Broglie had postulated that electrons have a wavelength, given in A, of ... 

As the diameter of the catalyst particle is supposed to be close to that of the single-shell tubule[20], or to that of the inner tubule [8], the number of graphitic layers might depend on the flow rate of acetylene at the catalyst particle. The graphitic layers are supposed to be formed by the Cj units formed on the catalyst particle, exceeding those needed for the growth of the multi-shell tubule inner layer. This generalisation to multi-layer tubules is just a hypothesis, since we do not have any experimental proof yet. 

Experimental proof of the nature of the hydroxyl groups was provided in the following way (Adams and Hamlin) —... 

Beleg, m. covering, coating, lining plating incrustation floor proof document, -ana-tyse, /. analysis giving experimental proof check analysis. 

Fig. 10-3. Experimental proof that x-ray emission speetrography and radioactivity both conform to the unique Gaussian fluctuation curve based on N alone. Crosses = data of Rutherford and Geiger circles = x-ray emission data solid line = theoretical Gaussian curve. (Liebhafsky, Pfeiffer, and Zemany, Anal. Chem., 27, 1257.)...

Unfortunately, direct experimental proof of this mechanism is not available. Kinetic data (see below) offer none since the interpretation need not be unique—more than one mechanism can serve equally well. In addition, the physical properties of the catalyst are obviously contributing, and, in the extreme, diffusion can be rate-controlling, completely obscuring chemical mechanisms. 

Hantzsch was unable to provide any direct experimental proof for his hypothesis. His grounds for assigning configurations were the analogies to oximes, such as the differences in stability already mentioned. 

A hypothesis suggesting a relation between the AEmv and molecular weight governing mechanisms has been proposed, which state that AEmv s = —6.6 + 1.0, -4.6 +1.0 and —1.8 1.0 reflect three different molecular weight governing mechanisms transfer to monomer, a combination of transfer to monomer and termination, and termination, respectively. Experimental proofs in support of this hypothesis have been obtained by Mayo plot analyses and model experiments. 

Figure 1.26 provides an experimental proof to above through profiles of initial conductivity erg. sensitivity to CO 5" = [ d<7 / di) and... 

It has been proven by experiment that there are donor acceptor atoms and molecules of absorbate and their classification as belonging to one or another type is controlled not only by their chemical nature but by the nature of adsorbent as well (see, for instance [18, 21, 203-205]). From the standpoint of the electron theory of chemisorption it became possible to explain the effect of electron adsorption [206] as well as phenomenon of luminescence of radical recombination during chemisorption [207]. The experimental proof was given to the capability of changing of one form of chemisorption into another during change in the value of the Fermi level in adsorbent [208]. 

The above 7AI analogs serve as one of the few experimental proofs for the solvent-induced barrier in proton transfer reaction. It is thus believed that through... 

The involvement of organocopper intermediates in various cross-coupling reactions carried out in the presence of Cu1 is often suggested, although in the majority of cases no experimental proof is provided, and the actual role of Cu1 may be different (Section 9.6.3.2.1). The potential of copper-mediated cross-coupling can be shown by the stereospecific reaction of 3-trimethylsilylallylic alcohols, which takes place via a prior transmetalation of Si to Cu (37).157... 

Subsequently, and although no experimental proof was accessible, it was commonly agreed that CTCs are active intermediates in bromination. In particular, Olah et al. (1974a) concluded from nmr spectra that the bromine-... 

The initially expected (75) cis-hydrometallation or olefin-insertion step with fumarate (R = C02Me) yields the threo isomer 8, which then undergoes the k2 step with retention to give racemic 1,2-dideuterosuccinate. Such retention is necessary to give the usually observed (7, p. 407) overall cis addition of H2 to olefinic bonds, but this study provided the first direct experimental proof, the difficulty being the scarcity of stable metal alkyl-hydride intermediates. The Cp2MoH2 complex also catalyzes hydrogenation of 1,3- or 1,4-dienes to monoenes (197). 

The experimental proofs of the chain mechanism of hydrocarbon oxidation are the following [2,3,7-15],... 

In 1965 1967 a great interest has been attached to the possible role of free radicals in cancer after studies by Emanuel and his coworkers who reported the excessive production of free radicals in tumor cells (see, for example, Ref. [145]). On these grounds the authors suggested to apply antioxidant therapy for the treatment of cancer patients. Unfortunately, experimental proofs of overproduction of free radicals in cancer tissue turn out to be erroneous [146], A new interest in the role of free radicals in cancer development emerged after the discovery of superoxide and superoxide dismutases. 

William Rankine was the first to propose the first law of thermodynamics explicitly, in 1853 (he was famous for his work on steam engines). The law was already implicit in the work of other, earlier, thermodynamicists, such as Kelvin, Helmholtz and Clausius. None of these scientists sought to prove their theories experimentally only Joule published experimental proof of the first law. 

Digressing from reductive desulfurization into stereochemistry, we may use this experimental proof of the equivalent symmetry of D-mannitol as a basis for an independent proof of the configurations of D-mannitol and D-arabitol. The reduction of D-arabinose yields the optically active pentitol, D-arabitol application of the Sowden-Fischer synthesis to D-arabinose yields D-mannose86 which upon reduction gives D-mannitol. 

Another proof of the configuration of D-mannitol and also of D-manno-n-manno-octitol (XVI), which is likewise dependent on the experimental proof of the equivalent symmetry of D-mannitol is the following. D-Mannose has been converted, by successive cyanohydrin syntheses, first to a mannoheptose and then to a mannooctose which on reduction yielded a mannooctitol whose octaacetyl derivative is optically inactive. (It was not possible to examine the octitol itself because of its very low solubility in water.)87 The meso character of the octaacetate shows that the mannooctitol must possess a meso configuration, with a plane of symmetry between carbon atoms 4 and 5. To write its formula, the hydroxyl at carbon atom 7 is placed on the... 

It so happened that 30 years later to the day I gave a research colloquium at Manchester University in which I could report that this job had now been completed, and we have in this paper the experimental details and the results concerning the title reaction which form the basis for the theory expounded in Section 4.5. The central point is the experimental proof that in very pure systems the principal initiating species is the A1X2+ ion (X = Cl or Br). Whilst this idea was quite old as a theoretical suggestion, its experimental verification had not been attempted previously. 

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