Symmetrical long-chain secondary alcohols
in the solid state show very high dielectric loss at audio and radio
frequencies. This can be explained by the presence of chains of hydroxyl groups
linked by hydrogen bonding and capable of reversing their direction. Further
evidence of hydrogen bonding is provided by a study of the melting points of
the secondary alcohols and related compounds.
The amount of dielectric loss depends
markedly on the manner of formation of the solid, being smallest for samples
formed by recrystallization from solvents at low temperatures and largest for
specimens obtained by slow cooling from the melt. The alcohols of molecular
chain-lengths of 13, 15,17, and 19 carbon atoms show a considerable decrease of
absorption on storing at room temperature. For alcohols of between 23 and 43
carbon atoms the loss is rather smaller with a peak at higher frequencies, but
remains more constant in time.
These results are interpreted in terms of competing
influences of van der Waals forces and hydrogen bonds during crystal formation
; the former, which lead to a structure unsuitable for the formation of
hydrogen-bond chains, are predominant at low temperatures, but become more
rapidly neutralized by thermal motion, especially for the shorter molecules.
The high temperature modification of the lower homologues is unstable at room
temperature, and a molecular diffusion process causes the bond chains to break.
Dilute systems of secondary alcohols with
hydrocarbons or paraffin wax of similar molecular chain-length show very small
dielectric loss suggesting a solid solution in which bond chains cannot be
formed ; if the paraffin molecules are appreciably longer, the absorption is
large and decreases on storing, presumably owing to the presence of a pure
alcohol phase. I.
PHOTODYNAMIC HEMOLYSIS AT LOW TEMPERATURES
