Additivity of substituent effects in the fluoroarene series: equilibrium acidity in the gas phase and deprotonation rates in ethereal solution

Benzene and all mono-, di-, tri, tetra-, and pentafluoro-substituted derivs. thereof were equilibrated with the corresponding aryl anions in the gas phase. Perfect additivity of the substituent effects on the acidity was obsd. The basicities were diminished by 12, 6, and 4 kcal/mol, depending on whether the supplementary fluorine atom occupied the ortho, meta, or para position with respect to the deprotonation site. On the other hand, substituent effects on the rates of hydrogen/metal interconversion processes level off with increasing nos. of halogens. For example, while the free energy of activation of sec-butyllithium-promoted lithiation of fluorobenzene is at least 4 kcal/mol smaller than that of benzene, the difference was found to shrink to less than 2.5 kcal/mol when pentafluorobenzene and 1,2,3,4-tetraflorobenzene were compared. [on SciFinder (R)]


Published in:
Tetrahedron Letters, 38, 49, 8519-8522
Year:
1997
Keywords:
Note:
CAN 128:88533
22-12
Physical Organic Chemistry
Nieuwe Achtergracht 129,Institute of Mass Spectrometry,Amsterdam,Neth.
Journal
0040-4039
written in English.
71-43-2 (Benzene); 327-54-8 (1,2,4,5-Tetrafluorobenzene); 363-72-4 (1,2,3,4,5-Pentafluorobenzene); 367-11-3 (1,2-Difluorobenzene); 367-23-7 (1,2,4-Trifluorobenzene); 372-18-9 (1,3-Difluorobenzene); 372-38-3 (1,3,5-Trifluorobenzene); 462-06-6 (Fluorobenzene); 540-36-3 (1,4-Difluorobenzene); 551-62-2 (1,2,3,4-Tetrafluorobenzene); 1489-53-8 (1,2,3-Trifluorobenzene); 2367-82-0 (1,2,3,5-Tetrafluorobenzene) Role: PRP (Properties) (additivity of substituent effects on the acidity of fluorobenzenes and deviation from additivity in their lithiation kinetics)
Laboratories:




 Record created 2006-03-03, last modified 2018-01-27


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