SOME PROPERTIES AND TRENDS OF ENTHALPIES OF VAPORIZATION AND OF TROUTON RATIOS OF ORGANIC-COMPOUNDS - CORRELATION OF ENTHALPIES OF VAPORIZATION AND OF ENTHALPIES OF FORMATION WITH NORMAL BOILING POINTS

Enthalpies of vaporization of homologous series n-RY (Y = H, Cl, Br, I, OH, SH, NH2, CN, COOH, OAc, and COOMe) or n-R1YR2-n (Y = O, S, NH, CO) have been correlated with the respective carbon numbers or sums of carbon numbers. These correlations imply that enthalpies of vaporization of any two series are linearly related to each other. Other important implications of these correlations are (a) from the stand point of thermochemistry the fundamental unit of a normal alkyl is a methylene group and (b) the contribution to the enthalpy of vaporization of an alkyl group is transferable and additive. Enthalpies of vaporization of sequences of compounds with normal alkyls plot linearly against the respective enthalpies of formation. Branched alkyls are in all cases below the regression line. This is taken to be a thermochemical manifestation of the steric effect of branched alkyl groups. A set of steric substituent constants of branched alkyls from C3 to C5 has been derived from thermochemical data. Enthalpies of vaporization of sequences of compounds which belong to the same class, e.g. halides, are shown to be linearly related to the respective normal boiling points. A number of correlations between enthalpies of formation and normal boiling points are also reported. Trouton's ratios of homologous series of compounds n-RY or n-R1YR2-n are correlated with the respective carbon numbers or sums of carbon numbers. A method is proposed for estimating normal boiling points of high-boiling organic compounds with normal alkyl chains.