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Additivity of Proton affinities: Theoretical studies of fluorine‐ and methyl‐substituted benzenes
Author(s) -
Eckertmaksić M.,
Klessinger M.,
Maksić Z. B.
Publication year - 1995
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.610080608
Subject(s) - chemistry , fluorobenzene , protonation , affinities , proton affinity , toluene , proton , computational chemistry , ring (chemistry) , ground state , additive function , medicinal chemistry , stereochemistry , ion , organic chemistry , benzene , atomic physics , mathematical analysis , mathematics , physics , quantum mechanics
Ring proton affinities ( PA s) in fluorobenzene and toluene were examined by the MP2(fc)/6–31G**//HF/6–31G* + ZPE (HF/6–31G*) model. The calculated PA s are in good accordance with the available experimental evidence, their order being PA ( p ) > PA ( o ) > PA ( m ) > PA ( i ), where p , o , m and i stand for para , ortho , meta and ipso positions, respectively. The relative values of the proton affinities can be interpreted in terms of the ground‐state charge distribution (initial state effect) and the characteristic π‐bond fixation produced by protonation (final state effect). The influence of the latter is either concerted with the initial charge distribution leading to higher PA s ( ortho and para positions) or disconcerted as in meta protonation, which has a lower PA value. Finally, it is shown that PA s in difluorobenzenes and fluorotoluenes are additive and can be reduced to the characteristic PA s of fluorobenzene and toluene with good accuracy.