engleski

Recent progress in high accuracy calculations of basicity of organic superbases

Synthetic utility of organic superbases has been recognized and covered in several excellent reviews. By definition, superbases are organic molecules which are stronger bases than archetypal ‘proton sponge’, 1, 8-bis(dimethylamino)naphthalene, i.e. they have the absolute proton affinity (APA) larger than 245.3 kcal mol-1 and gas-phase basicity (GB) over 239 kcal mol-1. Design and synthesis of novel neutral organic superbases is an important scientific target nowadays and many efforts has been laid in developing building blocks that can be combined together ending up in highly basic molecule. Nitrogen containing building blocks such as guanidines, amidines, phosphazenes, polypyridines and proazaphosphatranes are singled out as the most potent in this respect. As an important part of design of new superbases, quantum-chemical calculations are indispensable tool. In recent years, there have been extensive efforts put in the accurate calculation of PAs, gas-phase basicities (GB), and solution pKa values of organic bases. Results obtained by these calculations vary depending on the level of sophistication of the applied calculations. Although the fit to experimental values vary with the employed theoretical model, the relative order of basicity and general trends are followed for various calculation methods. To generalize, more high level of theory method employed - better is the correlation with the experimental results, however this statement is not always true. Large molecular systems present a special problem, due to their size, some trade-off between accuracy and computational efforts (CPU time) is needed. It should be noted that the most of theoretical work published in literature has been associated with the calculations of thermodynamic basicities, while scarce reports deal with the kinetic basicities of organic superbases.

quantum chemical calculations, basicity, superbases

nije evidentirano