Quantum mechanical calculations data available

Inadequate availability of experimental data can considerably inhibit the development of improved energy functions for more accurate simulations of energetic, structural, and spectroscopic properties. This has led to the development of class II force fields such as CFF and the Merck Molecular Force Field (MMFF), which are both based primarily on quantum mechanical calculations of the energy surface. The purpose of MMFF, which has been developed by Thomas Halgren at Merck and Co., is to be able to handle all functional groups of interest in pharmaceutical design. 

No data are available for compounds with C=Se and C=Te bonds and their equilibria with the seleno- and telluro-enol tautomer. For simple selenoacetone, its tautomer, and telluro-analogues, quantum mechanical calculations have been carried out using different methods.5 These calculations have shown that on passing from O to Te, the energy difference between the tautomeric forms is reduced, a trend that parallels the calculated C=E bond energies, which decrease from O to Te. 

The electronic structure and physical properties of any molecule can in principle be determined by quantum-mechanical calculations. However, only in the last 20 years, with the availability and aid of computers, has it become possible to solve the necessary equations without recourse to rough approximations and dubious simplifications2. Computational chemistry is now an established part of the chemist s armoury. It can be used as an analytical tool in the same sense that an NMR spectrometer or X-ray diffractometer can be used to rationalize the structure of a known molecule. Its true place, however, is a predictive one. Therefore, it is of special interest to predict molecular structures and physical properties and compare these values with experimentally obtained data. Moreover, quantum-mechanical computations are a very powerful tool in order to elucidate and understand intrinsic bond properties of individual species. 

There have been no papers with experimental thermochemical data for 1,2,3-thiadiazoles. Thermochemical data derived from quantum mechanical calculations for 1,2,3-thiadiazoles are also not available. These areas clearly are worthy of greater research attention. 

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