Determination of descriptors for semivolatile organosilicon compounds by gas chromatography and non-aqueous liquid-liquid partition.

The measurement of retention factors by gas chromatography on up to 15 stationary phases at several temperatures in the range 60-240 degrees C for each stationary phase and liquid-liquid partition coefficients in three biphasic organic solvent systems (n-hexane-acetonitrile, n-heptane-N,N-dimethylformamide, and n-heptane-2,2,2-trifluoroethanol) were used to calculate solute descriptors for 28 semivolatile linear and cyclic organosilicon compounds for use in the solvation parameter model. Regression analysis for oligomeric compounds allowed the descriptor values for the dimethylsiloxane, diethylsiloxane, methylvinylsiloxane, and methylhydrosiloxane monomer groups to be estimated. These monomer groups contribute significantly to the hydrogen-bond basicity (B descriptor) and cavity formation and dispersion interactions (L and V descriptors) of oligomeric organosilicon compounds, are non-hydrogen-bond acidic (A descriptor=0), are slightly less dipolar/polarizable than an n-alkane (S descriptors are negative and close to zero), and bind electron lone pairs more tightly than an n-alkane (E descriptor is small and negative). The semivolatile organosilicon compounds with polar functional groups in their side chain demonstrate a much wider range of selective intermolecular interactions than alkylsiloxanes and have solvation properties closer to those of polar organic compounds.