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Non‐additivity of the static correlation energy of π‐electrons in planar molecules as a manifestation of anti/aromaticity
Author(s) -
Barić Danijela,
Maksić Zvonimir B.
Publication year - 2003
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.666
Subject(s) - antiaromaticity , aromaticity , chemistry , molecule , computational chemistry , additive function , chemical physics , homo/lumo , formalism (music) , organic chemistry , mathematical analysis , mathematics , art , musical , visual arts
The non‐dynamic or static correlation energy of π‐electrons, E (ND) π , was studied in a number of cyclic organic molecules, including various heteroatomic systems, employing CASSCF π formalism. It is shown that E (ND) π is highly additive in linear polyenes. However, interesting non‐additivities are found in anti/aromatic molecules. They are seemingly counterintuitive since E (ND) π is smaller in aromatic compounds than in the corresponding open‐chain polyenes. The opposite takes place in antiaromatic systems. However, they are easily understood if it is taken into account that the HF HOMO–LUMO gaps are higher in aromatic and lower in antiaromatic molecules compared with reference zig‐zag polyenes. The results of the present analysis confirm that anti/aromaticity is an excess or depletion feature, meaning that deviations of E (ND) π from additivity are a direct consequence and clear manifestation of anti/aromaticity. It is argued that anti/aromaticity is necessarily a multifaceted phenomenon, since each molecular property probes different portions of the electron density distribution and/or a ladder of the molecular orbital energy levels, thus leading to distinct scales of anti/aromaticity. Each of these scales is useful in its own right. However, the most important scale is based on homodesmotic reactions, since they are directly related to thermodynamic in/stability and consequently to the omnipresent chemical reactivity. Copyright © 2003 John Wiley & Sons, Ltd.