Group-contribution values are presented and, together with those already developed for the aliphatic hydrocarbons (10, 11), make possible the evaluation of both van der Waals' constants for the naphthenic hydrocarbons. These constants can be used to produce the critical temperatures, pressures, and volumes of these compounds entirely from a knowledge of their chemical structure.
Critical constants have been calculated for several naphthenes, and from a comparison of them with the constants resulting from the methods of Riedel (5, 6) and Lydersen (3) it was found that the critical constants calculated by these three methods were in fair agreement for naphthenes having short alkyl side chains and progressively deviated from each other as the chains were permitted to lengthen. An appraisal has been made on five naphthenes along the lines proposed by Sondak and Thodos (9) in order to see whether these calculated critical constants properly represent the vapor-pressure function resulting from vapor-pressure data found in the literature for these hydrocarbons.
Critical constants have been produced for more than fifty naphthenes, for which vapor-pressure data are available in the literature, and will be used in a separate, comprehensive vapor-pressure study for hydrocarbons of this type.