and found it to be negligible. Therefore, the effect of the quadru-
polar moment interaction with the fluorine nucleus may be neglected
for spin-lattice processes. o-Chlorofluorobenzene has one ortho
fluorine-hydrogen, two meta, and one para interactions. m-Chloro-
fluorobenzene has two ortho, one meta, and one para fluorine-hydrogen
interactions. p-Chlorofluorobenzene has two ortho, two meta, and no
para hydrogen-fluorine interactions. The fluorine-hydrogen dipolar
interactions in p-chlorofluorobenzene would therefore be efficient in
intramolecular dipolar relaxation, giving the smallest T intra d
1 intra d
The intermolecular dipolar contribution, T1 inter' follows the
sequence o < p < m at temperatures above 20 degrees Centigrade. Below
20 degrees Centigrade, T inter follows the sequence o < m,p until the
1 inter
freezing points are approached where the three values are about equal.
The BPP theory predicts that the intermolecular contribution, T1 inter'
is governed by diffusion, and T inter is inversely proportional to
the macroscopic viscosity as demonstrated in equation (3). A temper-
ature-dependence study of the macroscopic viscosity for the three
compounds was made. Figure 7 shows plots of the log of the viscosity
as a function of 1/T for o-, m-, and p-chlorofluorobenzene. Benzene
is shown as the reference material on the plot The plots are linear
as expected. The important point is that over the investigated temper-
ature range the magnitudes of the viscosities follow the sequence
o > p > m, or the inverse of T inter This result lends evidence to
1 inter
the fact that the intermolecular relaxation time is governed by
diffusional processes.