Quantum mechanical studies deficiencies

Reactions of cyclic and acyclic 1,2,3-triones with phenylhydrazine give rise to mono- and bis-(phenylhydrazones). The central carbonyl group of a vicinal tricarbonyl system is electron-deficient and highly electrophilic,255 which is why treatment with an aryldiazonium ion affords 2-phenylhydrazones. The structure of such bis(phenylhydrazones) as cyclopentane-1,2,3-trione 1,3-bis(phenylhydrazone), dehydroascorbic acid 2,3-bis(phenylhydrazone), and cy-clobutanetetraone l,3-bis(phenylhydrazone) has been studied by UV, IR,1H-, 13C-, and 15N-NMR spectroscopy.265-268 Quantum-mechanical calculations to predict the most stable tautomeric forms of some 1,2- and l,3-bis(phenylhydrazones) revealed that the chelated bis(hydrazone) structure was usually more stable than the azoene-hydrazine structure.269-271 This does not mean that such structures do not exist, for example cyclobutanetetraone l,2,3-tris(phenylhydrazone) exists in a stable phenylazoene-hydrazine structure (see 49 Scheme 8).257-263... 

There are, however, important limitations in the application of MD First, practical considerations limit the model system to relatively small sizes of 10 to 10 atoms. This makes it difficult to extrapolate the results of MD, and to compare them with those of macroscopic systems consisting of 10 atoms. Second, our knowledge of the interaction potentials among various kinds of atoms is seriously deficient. It is therefore difficult to compare MD results directly with real experiments. Moreover, chemical reactions are basically controlled by quantum mechanics, not classical mechanics. This imposes additional difficulties in MD simulations of chemical detonation. Third, only numerical solutions are available, and from these it is difficult to develop a broad theoretical understanding of the particular effect under study. Great care must be exercised in the interpretation of the numerical results, and in making certain that they are physically realistic, and are not simply an idiosyncrasy of the numerical model or the assumed boundary conditions. 

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