factor given by yN /N, and ZNM is the atomic number of the NI
nucleus. The I 's are the principal moments of inertia of the
molecule, and the C 's are the diagonal components of the spin-
rotation tensor about these principal axes. By use of the mean
moment of inertia defined in equation (19), the modulus of the spin-
rotation tensor may be written, after substituting for known con-
stants, as
-. 4.42 x 10 -44 13 ZN'
C 4.2 (1.06 x 101) a + Z (21)
Sp NIN RNN
for a fluorine nucleus. The paramagnetic contributions to the
shielding constants for o-, m-, and p-chlorofluorobenzene have been
calculated by Caldow [78]. He found the paramagnetic contributions
to be 7.49, -1.15, and 3.08 parts per million (ppm) from fluorobenzene
for o-, m-, and p-chlorofluorobenzene, respectively. Chan [20] has
measured the paramagnetic contribution for fluorobenzene to be -284
ppm. Using these paramagnetic shielding values, calculating the mean
moments of inertia, and using the previously mentioned bond distances,
the moduli of the spin-rotation tensors for o-, m-, and p-chloro-
fluorobenzene are obtained. The values are 3.85, 2.91, and 3.74 kHz
for o-, m-, and p-chlorofluorobenzene, respectively. Chan [76] found
the diagonal components of the spin-rotation tensor in fluorobenzene
to be -1.0, -2.7, and -1.9 kHz, giving a modulus of 2.0 kHz.
The modulus of the spin-rotation constant may also be experi-
mentally determined from equation (7), postulated by Hubbard to obtain