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432 12MAGNETIC RESONANCE
NO2
7.64 × 10−3
−
NO2
4.89 × 10−3
4.89 × 10−3
7.64 × 10−3
NO2
NO2
−
0.0498
0.0498
0.0498
0.0498
NO2
0.200
−
NO2
0.1210.200
0.048
Figure 12.15
P12D.8 Simple considerations indicate that the EPR spectrum of 1 will be a 1:1:1 triplet
on account of the coupling of the electron to a single 14N, which has I = 1. Elec-
tron exchange, resulting from the physical interaction of two radicals, results
in a scrambling of the spin state of the electron because the electron which
is exchanged has an equal change of being in the α or β spin states. Such
scrambling at �rst causes a broadening of the lines in the hyper�ne multiplet,
and if it is at a high enough rate the lines merge. For even faster rates, the
merged line narrows. �is is analogous to the e�ect that chemical exchange
has on the coupling patterns seen in NMR, Section 12B.4 on page 505.
Answers to integrated activities
I12.2 (a) �e spin densities, computed by molecular modelling so�ware (ab initio,
density functional theory, Gaussian 98), are shown below
O
CH3
0.409
0.271
− 0.082
− 0.129
0.369
0.299
− 0.135
− 0.024
�e computed spin densities for the the two protons ortho to the oxygen,
and to the two protonsmeta to the oxygen are di�erent.�is is undoubt-
edly a computational artefact, a result of the minimum-energy structure
having one methyl proton in the plane of the ring, which makes the right
and le� side of the ring slightly non-equivalent. Fast internal rotation