Safety note: Some of the materials mentioned here are very dangerous. Ask a qualified chemist for advice before handling them. Qualified chemists should check the relevant safety literature before handling or giving advice about unfamiliar substances. NMR solvents are toxic and most are flammable. Specifically, bromide is toxic in large doses. Other oxidation states of bromine are toxic: wear gloves.

Bromine NMR

Bromine (Br) has two NMR active nuclei, ⁷⁹Br and ⁸¹Br with a wide chemical shift range (fig. 1). Both nuclei are quadrupolar and therefore yield broad signals as ions in symmetrical environments and signals, too broad to be observed with a high-resolution NMR spectrometer, even in small molecules. As a result bromine NMR is restricted to relaxation studies of the binding of bromide ions. ⁸¹Br is the more sensitive nucleus and yields slightly narrower signals than ⁷⁹Br (fig. 2) so ⁸¹Br is the nucleus of choice. However, ⁷⁹Br has a frequency very similar to ¹³C (fig. 3) and is often observable using a carbon specific probe. Because of this and because it produces clear quadrupolar spinning sidebands in the solid state (fig. 4), it is widely used in solid state NMR for adjusting the magic angle. There is very little information about bromine chemical shifts (fig. 1).

Fig. 1. Chemical shift ranges for bromine NMR

Fig. 2. Comparison of ⁷⁹Br and ⁸¹Br for KBr in D₂O. ⁸¹Br is the more sensitive nucleus and yields narrower signals.

Fig. 3. The signal of ⁷⁹Br (right) in the same spectrum as the ¹³C signals (left) for KBr and acetone in D₂O. The chemical shift scales are for ¹³C (top) and ⁷⁹Br (bottom).

⁷⁹Bromine NMR

⁷⁹Br (fig. 5) is less sensitive and yields broader signals than ⁸¹Br so it is not usually the nucleus of choice for liquid NMR. However, ⁷⁹Br has a frequency very similar to ¹³C (fig. 3) and is often observable using a carbon specific probe. Because of this and because it produces clear quadrupolar spinning sidebands in the solid state (fig. 4), it is widely used in solid state NMR for adjusting the magic angle.

Fig. 4. ⁷⁹Br-NMR spectrum of solid KBr showing spinning sidebands used for adjusting the magic angle

Fig. 5. ⁷⁹Br-NMR spectrum of KBr in D₂O

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Properties of ⁷⁹Br

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⁸¹Bromine NMR

⁸¹Br (fig. 6) is the bromine nucleus of choice, at least for liquid-state NMR, as it is more sensitive and yields narrower signals than ⁷⁹Br.

Fig. 6. ⁸¹Br-NMR spectrum of KBr in D₂O

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Properties of ⁸¹Br

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References

1. G. Lindblom, B. Lindman and L. Mandell "Study of counter-ion binding to reversed micelles by nuclear magnetic quadrupole relaxation of bromine-81" J. Coll. Interface Sci., 34, 262-71, (1970).
2. P. Diehl, E. Fluck and R. Kosfeld, Eds., "NMR, Basic Principles and Progress, Vol. 12: Chlorine, Bromine and Iodine NMR. Physico-Chemical and Biological Applications." Springer, Berlin, Ger. (1976).
3. T. Drakenberg and S. Forsen, "[NMR of] the halogens - chlorine, bromine, and iodine" NATO ASI Series, Series C: Mathematical and Physical Sciences 103 (Multinucl. Approach NMR Spectrosc.), 405-44 (1983).

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