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Keywords: Acidity / Aromaticity / Electrostatic field effect / Substituent effectsThe acidities of mono-and polysubstituted benzenes incorporating one, two, or three OCH 3 , OCF 3 , or CF 3 groups were investigated by use of reliable ab initio theoretical models. The calculated deprotonation energies are in very good agreement with available experimental data, although these are unfortunately sparse. A recently developed novel trichotomy formula proved useful for interpretation of predicted variation in acidity in the monosubstituted compounds. In particular, the long-range final state effect in OCF 3 and CF 3 derivatives is confirmed. It is reflected in the stabilization of the lone-pair electrons formed upon deprotonation at the meta and para positions. The theoretically established long-

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ABSTRACT:We propose a new expansion for the Boys function H t exp yr t dt 0 appearing in the calculation of molecular two-electron matrix elements if Gaussian basis Ž . sets are employed. This expansion involves a power series involving the termsmultiplied by exp y r , where is an optimized parameter g 0, 1 . The performances of the introduced expansion are discussed and illustrated by some numerical experiments. It appears that the proposed expansion is considerably shorter than the customary Taylor series, which in turn is the special case for s 0. This is of some importance, particularly for higher j values. Further, the proposed expansion Ž . enables a single expression for calculating erf x for the whole range of variable x. The recursive relations for the expansion coefficients are derived and the truncation errors are estimated. A new method for calculating the Boys function by means of asymptotic series is represented too.