The total polar contributions (AP) to three properties [infrared absorbance, mixing enthalpies (HM)
and excess free energies (GE)] of alcohol + alkane (alp) systems are separated into a direct hydrogenbond
contribution ( AB) from the formation of isolated imers and a dipole-dipole contribution (AD)
resulting from dipolar correlation between these transient imers.
Dilute concentration range data giving the AB contributions to these properties were found
dependent only on OH group concentration (c) and are used to show the serious inadequacies of
previous theories. A new proposed association model having only two parameters, that are fixed
for all systems, does give good results for the AB contributions and further is quite compatible with
the effect of temperature change and with the n.m.r. chemical shift (ε) and apparent mean square
dipole moment (p2) data that are also studied. Thus association theory has been made quantitative
for the AB contributions to three properties of a/p systems and the approach given for deriving
models appears capable of wider application.
The model was used to extrapolate the AB contributions into the concentrated alcohol range to
thus give the AD contributions by difference. The latter are then shown to be the origin of the distinctive
behaviour shown by lower alcohols in their pure and binary mixture properties either with
alkanes or with other alcohols where for the latter the principle of congruence is shown to be completely
misleading.
Two contributions (Ag and AD) explain the different c dependence shown by the i.r., HM and
the δ data for a/p systems and, qualitatively, the HM data for alcohol+alcohol systems while the
existence of a significant dipole term is strongly supported by the remarkable similarities found
between the p2(c) data and the derived dipole-dipole contribution to the entropy of a/p systems.
A method is given for predicting latent heats and partial molar enthalpies of higher alcohols
from the HM data for one a/p system and a refined estimate is made of the enthalpy of formation
of a hydrogen bond. Polar structure and non-linear dielectric effects are also discussed.
Reverse vesicles as a new system for studying enzymes in organic solvents
