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The heat of sublimation of many nonionic organic and inorganic compounds at their lowest first-order transition point has been separated into group increments. The group increments have been tabulated. Various aids are presented for the calculation of heats of sublimation from a minimum of experimental data. For many compounds, the heat of sublimation can be estimated using only the increments presented.The HEAT OF sublimation of crystalline solids is useful not only in thermochemical calculations but also as one of the more important correlating parameters for many thermal and mechanical properties of solids. The rapid accumulation of experimental data from which heats of sublimation can be derived has made it worthwhile, therefore, to develop means by which this information could be generalized and extended. Moreover, quite a few published data are seriously in error. This can be demonstrated most simply by suitable correlation methods, such as the one proposed here.

A new method is proposed for the calculation of the heat of vaporization of hydroxylated compounds to an accuracy of about k0.5 kcal./mole from no more data than the molecular structure and a boiling point. The older methods, by comparison, achieved an accuracy of about i l kcal./mole with a far greater computational effort, since they required the (usually hypothetical) critical temperature and critical pressure in addition to a boiling point.The method is here applied to aliphatic and aromatic alcohols, to ether-alcohols (e.g., the cellosolves), and to alcohols containing keto or aldehyde groups (e.g., salicylaldehyde) and supersedes previous correlations covering the heats of vaporization of these compounds. The method can also be used to assess the quality of vapor-pressure data of the compounds covered by it.The method is based on the assumption that the heat of vaporization consists of two terms, the dispersion energy and the hydrogen-bond increment (close but not equal to the hydrogen-bond strength). The first term is calculated from a knowledge of the heat of vaporization of the equistructural hydrocarbon, now easily available from the Tables of A.P.I. Research Project 44. The hydrogen-bond term is calculated from a set of rules given in the report.The application of the increment method of this report to other properties and other functional groups is the subject of a continuing investigation. PURPOSE AND SCOPEThe recurrent need for heat-of-vaporization data of increasingly complex synthetic oxygenated compounds and the discovery of some inconsistencies in previous correlations prompted a short inquiry into regularities which could be used as basis for improved calculation. The choice between the direct calculation of the heat of vaporization and the older path of calculating the entropy of vaporization has been resolved in favor of the first route, since it could be shown from basic principles that more information is required to estimate the entropy of vaporization from liquids with strongly Donald J. Simkin is with Rlarquardt Aircraft Company, Van Nuys, California.