Acetylene negative ions

The spectra of the negative ions of the untreated silica powders (Fig. 8b) have no specific peaks such as from C , CH in the mass range of 0-40 amu, in contrast to the spectra of the acetylene-treated sample (Fig. 9b), which do show these C and CH- peaks again in this mass region. This is another proof of the surface coating on the silica powders. 

Carbene. )Same as Cuprene, (C, SH,0)X, a yel-bm polymerization product made by heating acetylene in the presence of Cu(Ref 1) 2)A positive or negative ion involving two- valentcarbon and paired electrons as in H2C , R2C or RZC++. These ions are different from methylene free radicals in that the latter have unpaired electrons. Carbenes have only transitory existence and are difficult or impossible to collect as such, but... 

It may be speculated that C60Hf, is best represented by structure 15. It is noteworthy that the formation of fullerene ions from acetylenic 14 is observed in the negative ion mode, which is considered to be milder than the positive ion mode which was previously used to detect ionized carbon spheres. It thus appears that 14 is structurally predisposed for fullerene formation. However, attempts to perform the exhaustive decarbonylation on a macroscopic scale by irradiating dilute THF solutions of 14 with pulsed laser light did not lead to the formation of buckminsterfullerene C6o-... 

Evidence for resonances in the cross sections for electron scattering from polyatomic molecules. Including hydrocarbons, can be found In the literature as far back as the late 1920 s (1,2). The authors of these papers, however, were unaware that the pronounced low energy peaks in the cross sections of molecules such as ethylene and acetylene were due to temporary negative Ion formation. Haas (3), In 1957, was apparently the first to observe that strong vibrational excitation accompanied such a peak, and to Invoke an unstable negative Ion complex as the means through which the excitation takes place. 

Fig. 7. Effect of mixture composition on negative-ion concentration. Acetylene/oxygen pressure, 2 Torr.

Alkynes (acetylenes) attract electrons so strongly that they form stable negative ions (Dodelet et al., 1973). 

In an earUer paper (1958) the authors described an enzyme system from another Pseudomonas species, which catalyzed the formation of p3nmvic from acetylene dicarboxyUc acid. They reason that the jS-addition of the negative ion to yield malonic semialdehyde which occurred with propioUc acid is expected and that pyruvic acid would not be the expected product of hydration of propioUc acid. Accordingly, even aUowing for the fact that a different enzyme is involved, the production of p3nmvic acid from acetylene dicarboxyUc acid indicates that hydration precedes decarboxylation. This is in agreement with Eimhjellen s findings. In the Pseudomonas system, however, oxaloacetic acid was not found as a free intermediate. 

Calcium carbide is the calcium salt of the doubly negative carbide ion (C=C ) Car bide ion is strongly basic and reacts with water to form acetylene... 

Often, the basic group that is responsible for the proton abstraction is also the nucleophilic group in the Michael addition. Thus, most of the suicide inhibitors made so far have been aimed at enzymes that catalyze the formation of carban-ions or carbanion-like intermediates. Suicide inhibitors are typically based on acetylenic compounds (as in equation 9.8), /3, y-unsaturated compounds (as in equation 9.9), or /3-halo compounds (as in equation 9.10). (The a protons in such compounds are acidic because the negative charge in the carbanion is delocalized by the conjugation with X.)... 

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