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)]
Keywords: Additivity; Free energy of activation; Protonation enthalpy; Substituent effects (additivity of substituent effects on the acidity of fluorobenzenes and deviation from additivity in their lithiation kinetics); Free energy (deprotonation; additivity of s ; substituent effect additivity acidity basicity fluoroarene; equil acidity gas phase fluorobenzene; deprotonation rate fluorobenzene ethereal soln
Physical Organic Chemistry
Nieuwe Achtergracht 129,Institute of Mass Spectrometry,Amsterdam,Neth.
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)
Record created on 2006-03-03, modified on 2016-08-08