Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Carbon compounds, aromatic, energies

Extensive approximate calculations of resonance energies foi molecules, especially the aromatic carbon compounds, have been made, and explanations of several previously puzzling phenomena have been developed.1 Empirical evidence has also been advanced to showr the existence of resonance among several valence-bond structures in many simple and complex molecules.2... [Pg.379]

The acid cleavage of the aryl— silicon bond (desilylation), which provides a measure of the reactivity of the aromatic carbon of the bond, has been applied to 2- and 3-thienyl trimethylsilane, It was found that the 2-isomer reacted only 43.5 times faster than the 3-isomer and 5000 times faster than the phenyl compound at 50,2°C in acetic acid containing aqueous sulfuric acid. The results so far are consistent with the relative reactivities of thiophene upon detritia-tion if a linear free-energy relationship between the substituent effect in detritiation and desilylation is assumed, as the p-methyl group activates about 240 (200-300) times in detritiation with aqueous sulfuric acid and about 18 times in desilylation. A direct experimental comparison of the difference between benzene and thiophene in detritiation has not been carried out, but it may be mentioned that even in 80.7% sulfuric acid, benzene is detritiated about 600 times slower than 2-tritiothiophene. The aforementioned consideration makes it probable that under similar conditions the ratio of the rates of detritiation of thiophene and benzene is larger than in the desilylation. A still larger difference in reactivity between the 2-position of thiophene and benzene has been found for acetoxymercuration which... [Pg.44]

Under aerobic conditions, aerobic bacteria has so far been only found in studies capable of reducing azo compounds and produce aromatic amines by specific oxygen-catalyzed enzymes called azo reductases. These aerobic bacteria could grow with mostly simple azo compounds as sole source of carbon and energy and under strict aerobic conditions by using a metabolism that started with reductive cleavage of the azo linkage. [Pg.88]

Fourth lesson - combination of different compounds in unique macrostructure provides unique performance properties. Starch is used extensively in nature to store carbon and energy. Starch is readily digested and must be protected from degradation by a resistant coating, for example, a seed (e.g. com, wheat or rice) or a skin (e.g. potato). Woody materials such as trees, soft plants and grasses are composed of a complex combination of aliphatic and aromatic compounds (cellulose, hemicellulose and lignin). [Pg.604]

However, not only the protonating ability of IIGeCh or systems derived from it determine the addition to aromatic carbon-carbon bonds, in contrast to the behavior of other HX acids. The specific features of HGeCl3 are probably manifested at the step of the cyclohexadiene derivative formation. Energy is obviously lost during the conversion from a-complex to cyclohexadiene. The formation of the cyclohexadiene-GeCl2 molecular complex (the GeCl2 present in the reaction mixture is a result of a well-known reaction, cf. Section III) is likely to be responsible for the equilibrium shift in the direction of the cyclohexadiene. It is likely that application of some other compounds which provide such shift by complexation with cyclohexadiene will enhance the addition of other HX acids to aromatic double bonds. [Pg.1514]

Benzene is a planar molecule. Each of its six carbon atoms is sp hybridized, with bond angles of 120°. A p orbital of each carbon overlaps the p orbitals of both adjacent carbons. The six tt electrons are shared by all six carbons. Compounds such as benzene that are unusually stable because of large delocalization energies are called aromatic compounds. [Pg.294]


See other pages where Carbon compounds, aromatic, energies is mentioned: [Pg.17]    [Pg.26]    [Pg.2]    [Pg.176]    [Pg.224]    [Pg.151]    [Pg.10]    [Pg.62]    [Pg.23]    [Pg.357]    [Pg.190]    [Pg.743]    [Pg.128]    [Pg.135]    [Pg.212]    [Pg.227]    [Pg.69]    [Pg.58]    [Pg.743]    [Pg.2]    [Pg.90]    [Pg.232]    [Pg.73]    [Pg.293]    [Pg.198]    [Pg.4992]    [Pg.332]    [Pg.176]    [Pg.177]    [Pg.198]    [Pg.475]    [Pg.255]    [Pg.265]    [Pg.351]    [Pg.427]    [Pg.90]    [Pg.349]    [Pg.455]    [Pg.155]    [Pg.24]   
See also in sourсe #XX -- [ Pg.379 ]




SEARCH



Aromatic carbon

Aromatic carbonates

Carbon aromaticity

© 2024 chempedia.info