Linear free energy relationship (LFER) models based on Abraham's solvation descriptors were developed and validated for the estimation of liquid vapor pressure (298 K) and normal boiling point of non-hydrogen bonding organic and organosilicon compounds.  A previously published LFER model developed for non-silicon containing compounds was found to be unsuitable for predicting vapor pressures of organosilicons.  This was due to the apparent failure of molecular volume to accurately represent the strength of dispersion interactions within the pure liquid, particularly for siloxanes.  When McGowan's characteristic volume (Vx) was replaced by the logarithm of the hexadecane-to-air partition coefficient (log L16) as the independent variable representing molecular size and polarizability, each property was successfully correlated to the compound descriptor values using a single equation having both chemical classes in its domain.  External validation was used to evaluate the predictive power of the models by dividing the combined dataset of approximately 230 organic compounds and 44 organosilicons into separate training and test sets.  Root mean square prediction errors for the test sets were 0.13 for the logarithm of the vapor pressure at 298 K (Pa), and 6.8 K for normal boiling point.  A small degree of class-specific bias was observed for prediction using the combined models, approximately 0.05 log units and 2.5 K on average, respectively. Separate models were validated for the organosilicons alone, which had similar overall performance characteristics.  These models are suitable for estimating properties of new compounds or for use in deriving their solute descriptors in combination with other measured properties having established LFERs.

General linear free energy relationship models for predicting vapor pressure and boiling point of organic and organosilicon compounds

246th National Meeting (2013)

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