engleski

Acidity of Substituted Benzenes - An Ab Initio Study of the Influence of Methoxy, Trifluoromethyl and Trifluoromethoxy Groups by Novel Trichotomy Formula

Acidity of mono- and polysubstituted benzenes involving one, two or three OCH3, OCF3 and CF3 groups is considered by using reliable ab initio theoretical models. The calculated deprotonation energies are in very good agreement with available experimental data, which are unfortunately sparse. A recently developed novel trichotomy formula proved useful in interpreting predicted variation in the acidity within monosubstituted compounds. In particular, the long-range final state effect in OCF3 and CF3 derivatives is confirmed. It is reflected in the stabilization of the lone pair electrons formed upon deprotonation at meta and para positions. The theoretically established long range influence of OCF3 and CF3 substituents is in accordance with empirical knowledge obtained by the experimental chemical reactivity studies. Acidity of multiply substituted benzenes exhibits additivity property which is based on the ISA (independent substituent approximation) model established earlier. It is conclusively shown that the additivity rule combined with trichotomy formula offers a powerful tool for rationalizing acidity of polysubstituted benzenes and mutatis mutandis of other multiply substituted aromatics, thus sheding a new light on this very old and important problem.

acidity; aromatics; substituent effect; electrostatic field effect

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