Compelling evidence

The trends in chemical and physical properties of the elements described beautifully in the periodic table and the ability of early spectroscopists to fit atomic line spectra by simple mathematical formulas and to interpret atomic electronic states in terms of empirical quantum numbers provide compelling evidence that some relatively simple framework must exist for understanding the electronic structures of all atoms. The great predictive power of the concept of atomic valence further suggests that molecular electronic structure should be understandable in terms of those of the constituent atoms. 

One example has already been encountered in the form of the binding constants in Table 3.2. These data form one of the first examples of compelling evidence for the involvement of attractive arene -arene interactions in determining the outcome of enantioselective catalysis. These attractive interactions have been frequently invoked as explanations for the observed enantioselectivities of... 

The state of nitric acid in g8-ioo% sulphuric acid In this section the pioneering work of Hantzsch will several times he mentioned. That later techniques made it necessary to modify his conclusions should not be allowed to obscure the great originality of his approach since investigations using these media provided the most compelling evidence for the existence of the nitronium ion. 

Although the nitronium ion cannot be detected by physical methods in these media, kinetic studies using these solutions have provided compelling evidence for the formation and effectiveness of this species in nitration. 

The nature of the hormone—NP link is unclear. Although the binding is quite specific, it is sufficientiy weak, ie, binding constant 10 10 M (71), as to cast doubt upon a protective role. However, no compelling evidence for a biological function for the neurophysins, other than as hormone carriers, has been elucidated (59,72). 

There is compelling evidence that both short- and long-term differences in diet result in alterations in the levels of phytoestrogens present in humans. Analysis of... 

Thiazine has been formulated as 1 rather than 2 because it does not form a sulfonamide under Hinsberg conditions. Symmetrical azines can form only one classical monocation, e.g., pyrazine forms 3. The nonclassical cation 4 has been postulated for pyridazine, but there is no compelling evidence in its favor. 

Of course, a single example hardly furnishes compelling evidence that equal volumes of any pair of gases (at the same temperature and pressure) contain equal numbers of molecules. Neither can we be convinced on the basis of simplicity when we have but one example. However, many gases behave as simply as a mixture of hydrogen chloride and ammonia. For example,... 

Primary and secondary aliphatic amines, morpholine and 2-methylaziridine and aniline and even the sterically hindered 2.2,6,6-tetramethylpiperidine readily react with 6-bromo-trithiadiazepine 7, in certain cases in the presence of /V./V-diisopropylethylamine, at room temperature by substitution of the bromine atom ammonia, for example, yields trithiadiazepin-6-amine 22 (R1 = R2 = H). There is compelling evidence that these reactions proceed by an elimination-addition mechanism via the heteroaryne, trithiadiazepyne 21.391... 

The identification of both phenylethyl and 1-phenyl-1,2,3,4-lelrahydronaphthalenyl end groups in polymerizations of styrene retarded by FeCl3/DMP provides the most compelling evidence for the Mayo mechanism.316 The 1-phenyl-1.2,3,4-tetrahydronaphthalenvl end group is also seen amongst other products in the TEMPO mediated polymerization of styrene,317318 However, the mechanism of formation of radicals 96 in this case involves reaction of the nitroxide with the Diels-AIder dimer (Scheme 3.63). The mechanism of nitroxide mediated polymerization is discussed further in Section 9.3.6. 

Eisch, Behrooz and Galle196 give compelling evidence for the intervention of radical species in the desulphonylation of certain acetylenic or aryl sulphones with metal alkyls having a lower oxidation potential at the anionic carbon. The primary evidence presented by these workers is that the reaction of 5-hexenylmagnesium chloride outlined in equation (85) gives a mixture of desulphonylation products, in accord with the known behaviour of the 5-hexenyl radical, in which the cyclopentylmethyl radical is also formed. 

Among the evidence for the existence of the E2 mechanism are (1) the reaction displays the proper second-order kinetics (2) when the hydrogen is replaced by deuterium in second-order eliminations, there is an isotope effect of from 3 to 8, consistent with breaking of this bond in the rate-determining step. However, neither of these results alone could prove an E2 mechanism, since both are compatible with other mechanisms also (e.g., see ElcB p. 1308). The most compelling evidence for the E2 mechanism is found in stereochemical smdies. As will be illustrated in the examples below, the E2 mechanism is stereospecific the five atoms involved (including the base) in the transition state must be in one plane. There are two ways for this to happen. The H and X may be trans to one another (A) with a dihedral angle... 

Although alkali-metal salts of trisimido organophosphates [R PlNRlj] have not been isolated and structurally characterized compelling evidence for their... 

Pathological observations indicate that lesions of the cardiovascular system can be a cause of death in patients with anaphylaxis [2], Myocardial lesions might be the anatomical basis for the irreversible cardiac failure occasionally associated with systemic anaphylaxis [3]. There is compelling evidence that the heart is directly and/or indirectly involved in several forms of anaphylaxis in man [1,4,5]. 

Hall et al. [62] identified in a separate study the same glycoprotein in H,K-ATPase vesicles isolated from porcine gastric mucosa. A stoichiometric ratio of 1.2 1.0 was found for the deglycosylated protein (35 kDa)/catalytic 94-kDa protein. Furthermore, compelling evidence that this glycoprotein is the H,K-ATPase p subunit was provided by N-terminal sequence analysis of three protease V8-obtained peptides of the 35-kDa core protein. These peptides showed 30% and 45% homology with the Na,K-ATPase pi and pi subunit, respectively. 

Other recent and very compelling evidence that the P subunit may also be necessary for full activity [83] comes from the study of a high threshold but DHP-insen-sitive brain channel that has an a 1-like channel core. The cDNA for this brain channel was recently isolated and the mRNA was expressed in Xenopus oocytes. The current corresponding to this channel was increased when the mRNA for either the skeletal muscle 0.2 or P subunits were co-injected. However, when the brain ai-like mRNA was co-expressed with the combination of the skeletal muscle 2 and p mRNAs, the current was dramatically increased from 31 nA for the brain ai alone to 6 500nA for the combination [83]. These striking results are the best evidence so far obtained that the P subunit has a functional role in channel activity. Although these data were obtained with a DHP-insensitive channel, they pro-... 

Further investigation of the possibility that inhibitors of the serotonin uptake carrier protect against serotonin depletion by /r-chloroamphetamine, fenfluramine, MDMA, MDA, and methamphetamine because they prevent the accumulation of those drugs within serotonin nerve terminals is warranted, but at present compelling evidence for this mechanism does not exist. 

Further studies were carried out with halocarbene amides 34 and 357 Although again no direct spectroscopic signatures for specifically solvated carbenes were found, compelling evidence for such solvation was obtained with a combination of laser flash photolysis (LFP) with UV-VIS detection via pyridine ylides, TRIR spectroscopy, density functional theory (DFT) calculations, and kinetic simulations. Carbenes 34 and 35 were generated by photolysis of indan-based precursors (Scheme 4.7) and were directly observed by TRIR spectroscopy in Freon-113 at 1635 and 1650 cm , respectively. The addition of small amounts of dioxane or THF significantly retarded the rate of biomolecular reaction with both pyridine and TME in Freon-113. Also, the addition of dioxane increased the observed lifetime of carbene 34 in Freon-113. These are both unprecedented observations. 

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