ChemDraw User's Manual - CambridgeSoft

Appendix E:WorksProHow ChemPropChemProp ValuesChemProp enables you to calculate predictedvalues of selected physical and thermodynamicproperties for structures of up to 100 atoms. Thefollowing topics describe how ChemProp obtainsits values.LogPLogP (partition coefficient for n-octanol/water)—three fragmentation methods are used to predictthe logP values.Method one is based on 94 atomic contributionsevaluated from 830 molecules by least squaresanalysis. This method works with a standarddeviation of 0.47 logP units and can handlemolecules containing hydrogen, oxygen, nitrogen,sulfur and halogens.1. Method two is an extension of method onethat is based on 120 atomic contributionsevaluated from 893 molecules by least squaresanalysis. In addition to the atoms introducedfor method one, it can handle molecules thatcontain phosphorus and selenium atoms. Thismethod works with a standard deviation of0.50 logP units.2. Method three is based on 222 atomiccontributions calculated from 1868 moleculesby least squares analysis. This method allows acalculation of logP with a standard deviation of0.43 logP units and can handle moleculescontaining hydrogen, oxygen, nitrogen, sulfur,halogens and phosphorus atoms. If thismethod is applied to molecules with internalhydrogen bonds, the standard deviation is 0.83logP units.Henry’s LawHenry’s Law Constant—The air to waterpartition coefficient that is expressed as ratio ofvapor pressure to water solubility or as a unitlessdistribution coefficient that can be evaluated as aratio of the concentration in air to theconcentration in water.Two methods are used to predict Henry’s Lawconstant.1. The first is an approach based on the bondcontribution method. This method uses 59bond contribution values and 15 correctionfactors. The contributions were calculated byleast squares analysis using a data set of 345chemicals. This method estimates with a meanerror of 0.30 units and a standard deviation of0.45 units and can handle molecules containingcarbon, hydrogen, oxygen, nitrogen, sulfur,phosphorus and halogens.2. In the second method, Henry’s Law constant isestimated from an equation found using linearregression. Multifunctional compounds wereomitted from this study. This method shouldnot be used for compounds where distant polarinteraction is present.ChemDraw 9 How ChemProp Works • 245LogP