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Cadmium has two NMR active spin ½ nuclei, 111Cd and 113Cd, that yield narrow signals (fig. 1) over a wide chemical shift range. 113Cd is very slightly the more sensitive nucleus and is therefore usually the preferred nucleus. Cadmium NMR is used for the study organocadmium compounds, cadmium complexes, inorganic cadmium and cadmium binding to proteins and other molecules of biological interest.
Fig. 1. Comparison of the (proton decoupled) NMR spectra of the cadmium isotopes 111Cd and 113Cd in neat dimethyl cadmium
Each type of cadmium compound has its characteristic chemical shift range (fig. 2).
Fig. 2. Chemical shift ranges for cadmium NMR
Both cadmium nuclei couple to other nuclei. 1H, 13C, 31P and 77Se couplings have been reported. On the coupling nucleus two set of couplings are observed as satellites as in the 13C spectrum in fig. 3. One bond couplings to 13C are typically around 500 Hz with the 111Cd coupling slightly smaller than the 113Cd coupling.
Fig. 3. 13C-NMR spectrum of Me2Cd showing coupling to both cadmium nuclei
Two and three bond couplings to 1H are typically in the region of 50 Hz. The difference between the 111Cd and 113Cd coupling constants with 1H is small so appear merged in the spectrum in fig. 4.
Fig. 4. 1H-NMR spectrum of Me2Cd showing apparently a single coupling to both cadmium nuclei
Resolution enhancment sepearates the two couplings (fig. 5).
Fig. 5. 1H-NMR spectrum of Me2Cd showing separate couplings to each cadmium nucleus
(111Cd) 111Cadmium is slightly less sensitive than 113Cd so is not usually the preferred nucleus of cadmium. It is a spin ½ nucleus and yields sharp signals (fig. 6).
Fig. 6. 111Cd-NMR spectrum of neat dimethyl cadmium showing coupling to 13C as satellite signals
Cadmium often shows couplings to other nuclei, 1H, 13C, 19F, etc. Cadmium couplings to protons can be removed by decoupling as in fig. 6. The coupled spectrum of dimethyl cadmium (fig. 7) shows a two bond coupling to 1H, (2J111Cd,H) of 49.6 Hz.
Fig. 7. 111Cd-NMR spectrum of neat dimethyl cadmium showing coupling to 1H
Property | Value |
---|---|
Spin | 1/2 |
Natural abundance | 12.80% |
Chemical shift range | 650 ppm, from -650 to 0 |
Frequency ratio (Ξ) | 21.215480% |
Reference compound | Me2Cd |
Linewidth of reference | 2.7 Hz |
T1 of reference | 0.65 s |
Receptivity rel. to 1H at natural abundance | 1.24 × 10-3 |
Receptivity rel. to 1H when enriched | 6.69 × 10-3 |
Receptivity rel. to 13C at natural abundance | 7.27 |
Receptivity rel. to 13C when enriched | 59.8 |
(113Cd) 113Cadmium is slightly more sensitive than 111Cd so is usually the preferred nucleus of cadmium. It is a spin ½ nucleus and yields sharp signals (fig. 8).
Fig. 8. 113Cd-NMR spectrum of neat dimethyl cadmium showing coupling to 13C as satellite signals
Cadmium often shows couplings to other nuclei, 1H, 13C, 19F, etc. Cadmium couplings to protons can be removed by decoupling as in fig. 8. The coupled spectrum of dimethyl cadmium (fig. 9) shows a two bond coupling to 1H, (2J113Cd,H) of 51.9 Hz.
Fig. 9. 113Cd-NMR spectrum of neat dimethyl cadmium showing coupling to 1H
Property | Value |
---|---|
Spin | 1/2 |
Natural abundance | 12.22% |
Chemical shift range | 650 ppm, from -650 to 0 |
Frequency ratio (Ξ) | 22.193175% |
Reference compound | Me2Cd |
Linewidth of reference | 2.5 Hz |
T1 of reference | 0.65 s |
Receptivity rel. to 1H at natural abundance | 1.35 × 10-3 |
Receptivity rel. to 1H when enriched | 0.0125 |
Receptivity rel. to 13C at natural abundance | 7.94 |
Receptivity rel. to 13C when enriched | 65.0 |
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, cadmium is a toxic carcinogen: wear protective gloves. Dimethyl cadmium is volatile: wear protective clothing and work in a hood. Latex gloves do not provide protection.