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DFT study of ionization potentials for aza‐substituted aromatic rings
Author(s) -
Barrio Laura,
Catalán Javier,
de Paz José L. G.
Publication year - 2002
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.10415
Subject(s) - lone pair , chemistry , ionization , ionization energy , basis set , atomic physics , homo/lumo , computational chemistry , density functional theory , ion , physics , molecule , organic chemistry
The ionization potentials of 20 azines and azanaphthalenes have been studied using Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar (B3LYP) method with 6‐31G** basis set at optimized geometries. Vertical ionization potentials (IP V ) have been calculated using Koopman's theorem (IP V = −ε HOMO ) and as the difference of single‐point energy calculations for the corresponding cation and for the neutral form (IP V = E cation − E neutral ). From our theoretical results most of the first ionizations come from the nitrogen lone pair and not from the highest occupied π‐orbital. Good agreement is found with experimental results when IP V is calculated from unrestricted B3LYP calculations of the neutral and the cationic species. The first π‐ionization follows Koopman's theorem for all monocyclic and bi‐cyclic systems under study. The lone pair repulsion effect is acceptably described by the energy of the highest n ‐orbital energy either for azines and azanaphthalenes. The annulation effect in the charged species is not reflected in the n –lone pair orbital energy of the neutral form and, consequently, it is not possible to find a fit that follows Koopman's theorem for lone pair orbital energies. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003