Reestimation of the Taft's substituent constant of the pentafluorophenyl group.
The Taft's substituent constant of the pentafluorophenyl group (sigma(C(6)F(5))) was reestimated to be 1.50 by correlation between IR spectral data (v(C)(=)(O)) and sigma constants for a series of esters (involving the pentafluorobenzyl group) of 3-phenylpropanoic acid and butanoic acid. The possibility of the disturbance of the correlation by the intramolecular pi-pi interaction between C(6)F(5) and C(6)H(5) groups in pentafluorobenzyl 3-phenylpropanoate was excluded by ab initio and DFT calculations of the stable conformations and their carbonyl frequencies. The reestimated sigma(C(6)F(5)) value was used for calculation of the pK(a) value of pentafluorobenzyl alcohol [14.5 (or 14.3)].
Department of Applied Chemistry, Faculty of Engineering, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan. korenaga@cc.okayama-u.ac.jp
Toshinobu
T
Korenaga
Koichi
K
Kadowaki
Tadashi
T
Ema
Takashi
T
Sakai