THERMODYNAMIC AND SPECTROSCOPIC ENTITIES

The idea of W. Luck to consider, in H bonded self-association, the equilibrium of the hydroxylic proton between a bonded and a non bonded state, irrespective of the situation of the lone pairs of electrons of the OH group is not an approximation but a necessity, when one takes into account that this situation is always changing in the liquid. The mobility and transferability of the H bonds in a liquid phase reduces the entropy with respect to a situation where this bond would be attributed to fixed partners. The direct consequence of this mobility is that the fraction γ of vapourizable molecules in an alcohol is not equal to the fraction γ:Ah of molecules a spectroscopist would recognize as completely free of H bonds, namely with both electron pairs and hydroxylic proton free. It is that γAh of the molecules with free protons irrespective the situation of the lone pairs. This is demonstrated by the comparison of the vapour pressure of ethanol at various temperatures and the spectroscopic determinations of γAh made by Luck. The fraction of time during which an alcohol molecule is vapourizable is thus not the fraction of molecules that a spectroscopist finds in the monomeric state. The mobility of the H bonds renders therefore void the rule that the time average and the ensemble average are the same. © 1990.