Cage strain

CL-20 (1987, A. Nielsen) and ONC (1997, Eaton) are without doubt the most prominent recent explosives based on molecules with considerable cage-strain. While CL-20 is now already produced in 100 kg quantities (e.g. by SNPE, France or Thiokol, USA, ca. 1000.-/2b) on industrial pilot scale plants, ONC is only avail-... 

Principally, members of both of the above mentioned classes of compounds (oxidation of the molecule back-bone ring and cage strain) can be exothermic or endothermic compounds. An example of the former is TNT with A H° = -295.5 kj kg-1, while RDX shows a positive standard enthalpy of formation of A H° = +299.7 kj kg"1. 

For an intermolecular transition (except charge transfer to solvent) the direction of the solvent shift is determined similarly. That is, if the Franck-Condon excited state has a larger dipole moment than the ground state, a red shift is observed with increase in solvating power of the solvent. Conversely, when the transition results in a decrease in dipole moment, there will be a blue shift contribution from solvent cage strain, which in most cases outweighs the dispersion red shift. 

Analysis of solvent shifts requires a knowledge of the transition concerned, and how this changes the dipole moment of the absorbing species. In interpreting observed shifts it is necessary to distinguish between polarisation red shifts (proportional to solvent refractive index), and shifts dominated by solvent cage strain, when solvent dipole moment may be more important. Nevertheless, in many cases the use of a simplified, approximate treatment yields useful information about both the ground and excited states. Examples of solvent shifts are included in the discussion of Types of Transition (sect. 4.4) and in Selected Applications (sect. 4.6). 

Fig. 2 Examples for EM that (i) show oxidation of the carbon backbone (left) [12], (ii) possess ring or cage strain (center) [13], or (iii) have very high positive heats of formation (right) [14]...

CL-20 (1987, A. Nielsen) and ONC (1997, Eaton) are without doubt the most prominent recent explosives based on molecules with considerable cage-strain. 

A new type of tautomerism involving a cage C-C bond, driven by cage strain in a CgQ derivative, has been reported (Scheme 5.15) [47]. The nine-membered hole in the cage of 21a was identified by NMR spectroscopy and the carbonyl group by... 

The basicity of PTA was measured in water at pK — 5.70. At pH lower than 6.5, 1 is A-protonated as the ammonium-phosphine [PTAHJX, (3). Further A-protonation is disfavored, as the increase in cage strain of PTA decreases its stability due to a change in hybridization of nitrogen centers [6]. 

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