where I is the mean moment of inertia calculated from
I-1 = 1/3 I 1 B Cl) (19)
T intra d may be calculated using equations (4) and (18). Values
of T1 intra d calculated by the Steele approach are given in Table 13
for o-, m-, and p-chlorofluorobenzene. The calculated values differ
from the experimental values by an order of magnitude. Steele pointed
out that the discrepancies which appear in his model were for the
values for molecules where a large molecular dipole is present. The
T intra d calculated by Steele is the maximum theoretical value based
on the fact that the molecule goes through one period of revolution
without spin exchange. The experimental values in each case are
shorter than the calculated values, indicating that there are possibly
several spin exchanges in one period of revolution.
Flygare [17,75] and Chan [20, 76,77] have shown that the spin-
rotation constant and the magnetic shielding constant for any molecule
can be related. Using LCAO-MO theory, Flygare showed that the para-
magnetic part of the shielding constant was equal to
2 iZN,
C 2 N (20)
3mc2 4(M)(gN) a C=a,b,c N1 N N'
where the nucleus in question is designated by N, and e is the electron
charge, RNN' represents the distance to the N' nucleus, m is the
electron mass, c is the velocity of light, h is Planck's constant, M is
the proton mass, pN is the nuclear magneton, g is the nuclear "g"