Condensed-hydrogen hypothesis

Chemists still didn t know why there were so many different chemical elements or whether any patterns could be found in them. In 1815 the English physician William Prout had proposed the hypothesis that all of the elements were condensed hydrogen. For example, the atomic weight of oxygen was 16. According to Prout, this indicated that 16 volumes of hydrogen had condensed to form this element. Of course Prout s hypothesis was incorrect. However, during the nineteenth century there was no empirical evidence that either supported or contradicted the idea. Consequently, some chemists adopted the theory while many others opposed it. 

The co-condensation reactions described above have led to the formation of interesting new compounds and sometimes very unexpected products. The nature of the products formed for example in the osmium atom experiments indicate high degrees of specificity can be achieved. However, the detailed mechanisms of the co-condensation reactions are not known. It seems most likely that in all cases the initial products formed at the co-condensation temperature are simple ligand-addition products and that the insertion of the metal into the carbon-hydrogen bond occurs at some point during the warming up process. In support of this hypothesis we note the virtual absence of any... 

The vaporization of a pure liquid or the reverse process, the condensation of the liquid, provides an interesting test of this delayed equilibration hypothesis. Thus as a hydrogen-bonded molecule, which vibrates in the liquid, separates from the surface it frees itself from the potential energy restrictions which prevented rotation. However, in so far as the evaporating molecule has insufficient collisions with neighbors to equilibrate to the free rotational partition function, fgy of the gas, it will retain substantially the partition function, fb of the condensed phase even in the activated complex. Consequently for the condensation process the usual... 

The reaction mechanism is still obscure, and the authors just suppose that the acidity necessary for getting the condensation of the OPUF nearby the anode, could arise from the acidic hydrolysis of Fe3+ cations originated by dissolution of the stainless steel anode. The applicative aspects of this system are noteworthy and further knowledge is necessary. Tidswell and Train110 ni>112) studied in great detail the homo- and copolymerization of vinyl acetate in aqueous emulsions. The possible initiation mechanisms are compared and the hypothesis of the formation of a vinyl acetate-hydrogen radical acting as true chain initiator is discussed. 

Xiao (1998) applied ab initio calculations to test the transition metal catalysis hypothesis. The key is to understand the kinetics and mechanisms of catalytic gas generation, promoted by transition metals through the activation of alkanes and the condensation of hydrogen and a-alkenes, as well as weather these reactions can proceed under realistic geological conditions. 

Theories on the in vivo synthesis of phytanic acid concentrate mainly on two possibilities. One of them deals with the possible formation of phytanic acid from isopren units or four molecules of mevalonic acid (or mevalonate), (Kahlke 1964 a, Kahlke and Richterich 1965). Instead of an end-to-end condensation of two molecules of famesyl pyrophosphate which results in the formation of squalene and finally cholesterol, a fourth active isoprenoid unit might be attached to famesyl pyrophosphate. From this intermediate several steps of hydrogenation and oxidation would be required for the formation of phytanic acid. This hypothesis now appears unlikely since Steinberg (1965) was unable to detect any activity in the phytanic acid fraction after administration of labeled mevalonate to a patient with HAP (case T.E. of Refsum). 

The results may be explained by the hypothesis that serine reacts with pyridoxal phosphate to form a Schiff base, that causes the labiliza-tion and subsequent dissociation of both the a-hydrogen and -hydroxyl group and removal as water (see Fig. 3, Chapter 14). The resulting product is an aminoacrylic acid derivative of pyridoxal phosphate enz3nne. Indole condenses at the double bond to form tryptophan upon dissociation from the enzyme. 

The fact that the formation of the benzimidazolone derivatives in the reactions of the self-condensation of 3-(a-azidophenylalkyl)quinoxalin-2(lf/)-ones 160 (Scheme 6.70) (Saifina 2009) and in the condensation of 3-(benzimidazo-2-yl) quinoxalin-2(17/)-one 37s with its predecessor-3-(benzimidazol-2-yl)methylene-quinoxalin-2(17/)-one 107 (Scheme 6.68) gives reason to propose a new hypothesis, that any of the spiro-derivatives of 1,2,3,4-tetrahydroquinoxalin-3-one without any mobile hydrogen atom in their spiro-forming component are on their way to the benzimidazolone derivative with the spiro-forming component at position 1 (Scheme 6.71). 

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