TY  - JOUR
AU  - Baric, D.
AU  - Kovacevic, B.
AU  - Maksic, Z. B.
AU  - Müller, T.
TI  - A Novel Approach in Analyzing Aromaticity by Homo- and Isostructural Reactions: An ab Initio Study of Fluorobenzenes
JO  - The journal of physical chemistry  / A
VL  - 109
SN  - 1089-5639
CY  - Washington, DC
PB  - Soc.
M1  - PreJuSER-51224
SP  - 10594
PY  - 2005
N1  - Record converted from VDB: 12.11.2012
AB  - The influence of fluorine substitutions on the stability of benzene is examined by using the Hartree-Fock (HF) and MP2 models. It is conclusively demonstrated that homodesmotic reactions based on the open-chain zigzag polyenes are unsatisfactory. A comparison of the intramolecular interactions of educts and products shows that they are not well balanced. Hence, these reactions should be abandoned in discussing aromaticity. A much better vehicle for exploring aromaticity is provided by homostructural reactions, which employ cyclic monoene and diene as reference model compounds. Their heavy atoms are enforced to assume planar geometries to enable sigma/pi separation. The HF/cc-pVTZ calculations show that extrinsic aromaticity of benzene B DeltaE(ease)(B)() arises both from the sigma- and pi-contributions. They are -14.8 and -23.1 in kcal/mol, respectively, if the stockholder energy partitioning scheme is employed. This result implies that both the sigma- and pi-frameworks contribute to the aromatic stabilization of B, the latter being more important. The total aromatic stabilization DeltaE(ease)(B)() is -37.9 kcal/mol. Schleyer's indene-isoindene isomerization approach also strongly indicates that the decisive factor in determining the aromatic stability of the benzene moiety is the pi-electron framework. The origin of extrinsic aromaticity is identified as the increased nuclear-electron attraction of both sigma- and pi-electrons, if 1,3-cyclohexadiene is used as a gauge compound. Further, by using a system of isostructural reactions, it is conclusively demonstrated that fluorobenzenes exhibit a remarkable additivity of the substituent effects, as far as the stability of multiply substituted benzenes is concerned. This additivity rule is so accurate that it enables delineation of the fluorine repulsions and the aromaticity defect DeltaE(AD). It appears that the DeltaE(AD) values increase upon sequential fluorine substitution at the next nearest (vicinal) position thus making multiply fluorinated benzenes less stable.
KW  - Butadienes: chemistry
KW  - Chemistry, Physical
KW  - Ethylenes: chemistry
KW  - Fluorobenzenes: chemistry
KW  - Hydrocarbons, Aromatic: chemistry
KW  - Hydrocarbons, Cyclic: chemistry
KW  - Hydrocarbons, Fluorinated: chemistry
KW  - Models, Chemical
KW  - Molecular Structure
KW  - Physicochemical Phenomena
KW  - Butadienes (NLM Chemicals)
KW  - Ethylenes (NLM Chemicals)
KW  - Fluorobenzenes (NLM Chemicals)
KW  - Hydrocarbons, Aromatic (NLM Chemicals)
KW  - Hydrocarbons, Cyclic (NLM Chemicals)
KW  - Hydrocarbons, Fluorinated (NLM Chemicals)
KW  - 1,3-butadiene (NLM Chemicals)
KW  - ethylene (NLM Chemicals)
KW  - J (WoSType)
LB  - PUB:(DE-HGF)16
C6  - pmid:16834316
UR  - <Go to ISI:>//WOS:000233436900016
DO  - DOI:10.1021/jp0532871
UR  - https://juser.fz-juelich.de/record/51224
ER  -