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left with five forms each of which was regarded as making a unique functional group contribution to the increment in properties. A further refinement, analogous to the interaction terms of the present investigation, was the introduction of terms specifying the number of primary, secondary, tertiary and quaternary carbon atoms adjacent to the olefinic group. One variable was found to be redundant and the resulting equation possessed eight terms. This equation when fitted to the increments in molal volume, molal refraction and normal boiling point gave average deviations of approximately three to five times those obtained for the paraffin hydrocarbons using a six term equation. Refinements to the Taylor, Pignocco, Rossini correlation (designated as TPR) might proceed along two lines. First a more detailed analysis of the steric interference terms could be made after the manner of the present investigation, and in which cis and trans isomers were distinguished. As an example, consider the three di-t-butylethylenes
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