1.2.4- Oxadiazoles chemical properties

In this chapter, as in CHEC(1984) and CHEC-II(1996) <1984CHEC(6)393, 1996CHEC-II(4)229>, the chemistry of compounds with the 1,2,5-oxadiazole ring system is considered. The history and nomenclature of these compounds, as well as basic synthetic methods and chemical properties of 1,2,5-oxadiazoles reported before 1996, were reviewed previously . This chapter covers the period from 1996 to 2006. 

Ab initio calculations, correlations of molecules geometries, spectroscopic data with chemical properties, and quanta-tive structure-activity relationship have been conducted for both furazans and furoxans. Thus, the structures of 1,2,5-oxadiazole (furazan) and benzo[c][l,2,5]oxadiazole (benzofurazan) have been calculated by ab initio and Becke3-LYP... 

The physical and chemical properties of the 1,2,4-oxadiazoles are also reviewed in this report. In particular, the stability of the ring system is discussed when only one or no substituent is present, and when the substituents contain functional groups. Attention is also particularly drawn to some novel routes of synthesis leading to the oxadiazole ring. 

Paolini and Cignitti140 and Kamiya111 attempted to correlate the electronic structure of 1,2,4-oxadiazole with its chemical properties. 

Oxadiazoles resemble in their chemical properties the corresponding 1,2,4-thiadiazoles (discussed in detail on p. 256) [462]. 

Unked polymers was enhanced compared to their Unear analogues since the formed oxadiazole rings can also interact with phosphoric acid contributing, thus, to the overall acid uptake of the final cross-linked membrane [32]. This fact strongly denotes the role of the chemical structure and the resulting morphology on the materials properties. 

The properties (chemical, physical, and spectral) of general ortho (structure I, benzo [d][l,2,3]oxadiazole) and para (structure II, 2-oxa-3,4-diazabicyclo[3.2.2] nona-l(7),3,5,8-tetraene) isomers of diazophenols are very similar indicating that the structures should also be similar. Even though the cyclization and formation of two rings does not seem to be unreasonable for the ortho-isomer, it definitely does not look probable for the para-isomer. It is therefore assumed that the structures I and II are rather improbable for diazophenols [5]. This assumption was confirmed when structure I was prepared and shown to be unstable even in a solid argon matrix. The meta-(3-diazo) isomer has not been reported [5, 6]. 

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