E. F. MEYER,T. A. RENNER, AND Iimateof the magnitude of die dispersion contribution in the alcohols, for while each alcohol is in the same corresponding state, there is no guarantee that it is the same one that the alkanes are in. The observation 1hat the alcohol plot is linear from C1to CI2indicates that the degree of association changes very little, if a i all, tis successive CH2 groups are added. The present approach to studying cohesive energies is thus not applicable to strongly hydrogen-bonded molecules. There is evidence that in flexible, long chain molecules coiling oocurs .in the vapor phase to a greater extent than in the liquid phase." This would have the effect of invalidating our equating cohesive energy to energy of vaporization. The latter quantity would be too small by lhe energy of coiling. I n fact, the plot for the paraffins shows a slight dropping off beginning with the C1*compound. Calculations using second virial coefficient data indicate that the drop-off cannot be due to impwfections in the vapor phase; it may be due to the coiling phenomenon. The excellent linearity of the plot below GI indicates that coiling is not significant in this range, and as long as we base our interpretation on thesc poinl s any coiling of vapor phase molecules would have no effect on our assumption. Equating cohesive energy with the energy of vaporization may be validly questioned even for molecules which are not long chains, We believe our doing so in the present study js justified for the following reasons. Any difference in internal energy of a given molecule in the vapor liquid phases arises either from a change in the number of classical degrees of freedom
The Journal of Physical Chemistry, Vol. 76, NO.6,2971
E. F. MEYER,T. A.
RENNEJI, AND
I
