Properties of Azides

An acyclic azide structure was rejected since the compounds show no azide IR absorption. A less likely three-membered ring was also considered. Comparison with other potential dihydro-SIV-thiatriazoles was made. Simple a-azido thioethers show the spectroscopic and chemical properties of azides rather than of dihydro-Slv-thiatriazoles. o-(Methylthio)phenyl azide was prepared but also showed the characteristics of an azide.70 These results cast doubt on the suggested structure, since the only essential difference in composition is an amino group that is not in a position to stabilize the suggested heterocyclic ring. Structure R1(R3R4N)C=N—N=N—SR2 is an alternative, but. further consideration must await X-ray crystallographic analysis. 

One of the most interesting features of the i.r. spectral properties of azides is the frequent occurrence of Fermi resonance. If an overtone or combination band falls near a fundamental frequency, the band intensity of the fundamental may he anomalously enhanced or the band may be split. This coupling between a fundamental frequency and the combination or overtone band is called the Fermi resonance. Certain symmetry properties must be met . ... 

The fundamental problem of why some azides (e.g. KNj) are not explosive whereas others (e.g. PbCNj) ) are, is still not fully understood. Nevertheless a great amount of information has been collected to date on various physicochemical properties of azides which can partly throw some light on the problem (see Table 73, Fig. 79 and 189]). 

Attempts to correlate the data from various types of apparatus have not been successful, and again a paucity of information on the properties of azides and the action of the stimulus has prevented the development of a universal standard test. To progress from the barely qualitative determinations of friction sensitivity... 

The present section reviews the optical and electrical properties of azides. The experimental techniques and methodology involved are discussed where this may be relevant to the interpretation of results. X-ray photoelectron spectroscopy is a powerful tool for studying the occupied electronic structure of azides it is reviewed in Section B of this chapter. 

Reviews containing detailed references to the optical and electronic properties of azides have been published by Evans et al. [5], Yoffe [1], and Young [64,99]. Optical absorption and luminescence results are reviewed here, with emphasis given to data relevant to the interpretation of features of the electronic structure. Frequent reference is made to the theoretical arguments of Section C. 

Historically, thermal and mechanical mechanisms for the initiation of fast reactions have been closely linked because, while it is common experience that explosions can be thermally initiated, it is also common to assume that the energy of any mechanical stimulus applied to an azide is first converted to heat before an explosion results (Chapter 8). Alternative mechanisms whereby the mechanical energy is absorbed as strain energy or in the fracture of crystals have not been given extensive consideration, although such possibilities have been proposed by Taylor and Weale [45], Ubbelohde [46,47], and others from the 1930s onward. The question of whether localized plastic flow or adiabatic shear can lead to the initiation of explosives under the action of low-intensity shocks has recently been given renewed attention [48]. Such considerations draw further attention to the lack of data on the mechanical properties of azides and explosives upon which to base quantitative assessments. Mechanical stimuli can also produce electric effects, and some of the possible consequences are discussed in the next section. 

Huang P (1981) The polarization of ions in metal azides and its influence on the properties of azides. J Beijing Inst Technol 2 37-43... 

In conclusion, thermoanalytical methods are powerful tools to determine safety-related thermal properties of azides. Whenever possible, we strongly recommend performing DSC measurements of potentially energetic azides as soon as a few milligrams of substance are available. The combination of DSC data on decomposition temperature and... 

The position of the TtO terms is determined by the azido group (or nitrene in the asymptote), which has similar structure in all azides depending slightly on the azide strueture as a whole. Conversely, the position of the term S ti is dietated by the aromatie n system of the azide. The relative arrangement of the terms So-, S tn and SrtCT determines the spectral and photochemical properties of azides. 

M.F. Budyka, l.V. Oshkin, A Quantum-Chemical Study on the Photochemical Properties of Azides of a Series of Heteroarenes from Pyridine to Dibenzoacridine in Neutral and Protonated Forms, High Energ. Chem.,2005,39,2 6 -223. 

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