Basic properties aromatic character

Aminothiadiazoles also react with halo aldehydes and halo ketones in a bidentate fashion to give imidazo[2,1-b ][1,3,4]thiadiazoles (145). The NMR properties, aromatic character, basicity and crystal structure data are available (80JCS(P2)42l). Aminothiadiazoles also react with trichloromethanesulfenyl chloride to give the sulfenamide (146) which in the presence of an aromatic amine cyclizes to 3//- [1,3,4]thiadiazolo[2,3-c ][1,2,4]thiadiazole (147) (75JOC2600). 

Several efforts have been made by many chemists to come to grips with universally acceptable notions of aromaticity, anti aromaticity and non-aromaticity as molecular properties. The results arrived at so far are at times rather frustrating, indicating the difficulty, if not the impossibility, of ascribing a consistent set of common distinguishing features to aromatic compounds [15]. Rules of aromaticity have been proposed by a number of researchers, see the chapter Rules of Aromaticity , by Feixas et al. in this book [125], assuming a basic connection between aromatic character and electron delocalization. 

Aromatic amines, containing the amino-group in the side-chain, have the basic character and properties of aliphatic cirrfines. 

Of course, in reality new chemical substances are not synthesized at random with no purpose in mind—the numbers that have still not been created are too staggering for a random approach. By one estimate,1 as many as 10200 molecules could exist that have the general size and chemical character of typical medicines. Instead, chemists create new substances with the aim that their properties will be scientifically important or useful for practical purposes. As part of basic science, chemists have created new substances to test theories. For example, the molecule benzene has the special property of aromaticity, which in this context refers to special stability related to the electronic structure of a molecule. Significant effort has gone into creating new nonbenzenoid aromatic compounds to test the generality of theories about aromaticity. These experiments helped stimulate the application of quantum mechanical theory to the prediction of molecular energies. 

The basic character of the imidazopyrazinone n-system. The physical properties of imidazopyrazinone derivatives 1-4 have been established by X-ray crystallography, UV/vis absorption spectroscopy, NMR, and a MO calculation. Since the imidazopyrazinone Jt-system contains an anti-aromatic 1,4-dihydro-... 

The basic structure of the building blocks of nucleic acids renders them inherently of no use for direct electronic properties. In contrast, the amide bond exhibits an important contribution of a double bond character, especially when it is electronically coupled to aromatic moieties [171,172]. 

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