Static Thermochemical Data

To be consistent the value of E2 should be corrected to constant pressure so that it represents AH for the process involved (flow system studies and static system work with excess inhibitor are essentially constant pressure experiments). Then D < E < D+RT. In the present work a reasonable estimate gives D — E—0J = 57.0 kcal.mole-1. Similarly, D2+D2 should be corrected to 0 °K, giving an estimated value of 59.0 kcal.mole-1. This gives D2 = 2.0 kcal.mole-1. Such corrections are normally within the limits of experimental error, so that experimental values of E are associated directly with dissociation energies, and thermochemical data at 25 °C are used. 

How can we assess the thermochemical data presented in Table 1 Many were obtained by static-bomb calorimetry. Regrettably, this technique is clearly unsuitable to deal with these substances due to the ill-defined composition of the combustion products (see the discussion in References 13 and 28). The formation of nonstoichiometric oxides upon combustion all but precludes the experimental rigor demanded of the combustion calorimetrist. This fact, by itself, allows us to question the reliability of the values shown for all of the trialkyl compounds and for triphenylantimony. Although the results for triphenylbismuth found by static and rotating-bomb calorimetry overlap within their error bars, this has been suggested to be fortuitous ... 

Thermochemical parameters of some unstable nitrile oxides were evaluated using corresponding data for stable molecules. Thus, for 2,4,6-trimethylbenzo-nitrile N-oxide and 2,4,6-trimethoxybenzonitrile N-oxide, the standard molar enthalpies of combustion and sublimation at 298.15 K were measured by static-bomb calorimetry and by microcalorimetry, respectively, this made it possible to derive the molar dissociation enthalpies of the N—O bonds, D(N—O) (17). 

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