Density functional studies of aniline and substituted anilines

In this work, we present an exhaustive study of the structural as well as the electronic properties of aniline obtained using several DFT based methods. The geometry of aniline obtained using the hybrid DFT methods (B3LYP, B3P86 and B3PW91) shows better agreement with the experimental values, than the methods containing the gradient corrected exchange functional (Becke 88). The new feature of the hybrid methods is that the exact Hartree-Fock exchange functional was taken in account. Negative highest occupied and lowest unoccupied Kohn-Sham orbitals (we shall call them as HOMO, LUMO) seem to provide a fair estimation of the experimental IPs and EAs values (particularly those obtained by using the gradient correct exchange functional Becke 88). IPs and EAs from DFT calculations present systematic errors are observed owing to the HOMO and LUMO, which do not correspond formally to any molecular orbital. We, also, study in a systematic way the influence of a wide range of sigma-pi electron donor-withdrawing substituent groups on the structural and electronic properties of aniline. In this kind of systems, the position of the substituent group in the benzene ring as well as its electron donor-acceptor capabilities play a very important role on the molecular structural and electronic properties. We also find that the intramolecular hydrogen bonds are responsible for many particular experimental features. (C) 1999 Elsevier Science B.V. All rights reserved.