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416 12MAGNETIC RESONANCE
each is the B–F coupling constant, and the multiplet is centred at the shi� of
the �uorine.
11B NMR: the 11B nucleus is coupled to four equivalent 19F nuclei, giving a
multiplet with 2nI + 1 lines; here n = 4 and I = 1
2 so there are 5 lines. �ese
lines have intensities in the ratio 1:4:6:4:1, each line is separated from the next
by the B–F coupling constant, and the whole multiplet is centred at the shi� of
the boron.
E12B.8(b) In 14NH+4 the four 1H nuclei are equivalent, and are coupled to a single 14N
nucleus with I = 1. �is splits the resonance into 2nI + 1 = 2 × 1 × 1 + 1 = 3
lines with intensity ratio 1:1:1.
In 15NH+4 coupling to a single 15N nucleus with I = 1
2 splits the resonance into
2nI + 1 = 2 × 1 × 1 + 1 = 2 lines with intensity ratio 1:1.
E12B.9(b) Coupling to a nucleus with I = 1 splits the original resonance into 2I + 1 = 3
lines of equal intensity: the lines appear at ν and ν ± J, where J is the coupling
constant. Coupling to a second spin-1 nucleus splits each of these three lines
into three in the same way. Because the two spins to which the coupling occurs
are equivalent, the coupling is the same and some of the lines fall on top of one
another, giving enhanced intensity.�e result is a 1:2:3:2:1 multiplet , as shown
in Fig 12.3.
JAX
ν increasing
Figure 12.3
E12B.10(b) �e multiplet resulting from coupling to two inequivalent I = 1 nuclei origi-
nates from the resonance of nucleus A being split into (2I + 1) = 3 lines by
coupling with the X1 nucleus, and then each of these lines being split into three
by coupling to the X2 nucleus.
Since the coupling between A and X1 is not the same as that between A and
X2, no lines are necessarily coincident and so nine lines of equal intensity are
observed, as shown in Fig. 12.4.