GROUP CONTRIBUTION-ADDITIVITY AND QUANTUM-MECHANICAL MODELS FOR PREDICTING THE MOLAR REFRACTIONS, INDEXES OF REFRACTION, AND BOILING POINTSOF FLUOROCHEMICALS
Td. Le et Jg. Weers, GROUP CONTRIBUTION-ADDITIVITY AND QUANTUM-MECHANICAL MODELS FOR PREDICTING THE MOLAR REFRACTIONS, INDEXES OF REFRACTION, AND BOILING POINTSOF FLUOROCHEMICALS, Journal of physical chemistry, 99(38), 1995, pp. 13909-13916
Group contribution-additivity (GCA) and quantum mechanical (QM) models
for estimating the molar refractions of fluorochemicals are proposed.
The GCA model was developed using experimental refractive indices and
densities, and the Lorentz-Lorenz electromagnetic correlation. The QM
model was developed using the distortion polarizability (alpha>) term
obtained from quantum mechanical calculations based on the PM3 Hamilt
onian. The GCA model provides molar refractive contributions for 23 he
terogeneous groups and atoms (e.g., R(F), R(H), C, N, O, F, Cl, Br, I,
C=O, NH2, OH, CH=C, CH=CH, CH2=C, CH=CF2, CF=CF2) and yields an absol
ute average error of less than 2% (n=100). The QM model, on the other
hand, offers unlimited groups but requires knowledge of the alpha desc
riptor. Methods for acquiring alpha are provided. Both models have bee
n successfully applied to the predictions of refractive index (n(D)) a
nd the normal boiling point (T-b) of fluorochemicals, with average err
ors of less than 1% and 6%, respectively. The higher method error obse
rved in the T-b model is attributed to errors introduced by T-b measur
ements at pressures slightly below 760 mmHg. The T-b model, nonetheles
s, provides accurate predictions of boiling point in the range between
30 and 230 degrees C.