Deuterium atomic absorption spectroscopy

Because most common solvents, including water, contain protons, and most NMR analyses involve the measurement of protons, a solvent without protons is generally used in NMR spectroscopy. Commonly, solvents in which the hydrogen atoms are replaced with deuterium (i.e., solvents that have been deuterated) are used, the most common being deuterochloroform. In addition, an internal standard, most commonly tetramethylsilane (TMS), is added to the sample in the NMR sample tube (see Figure 14.3, D) and all absorption features are recorded relative to the absorption due to TMS. 

Carboxylic acid groups can be detected by both and C NMR spectroscopy. Carboxyl carbon atoms absorb in the range 165-185 d in the C NMR spectrum, with aromatic and a,0-unsaturated acids near the upfield end of the range (-165 6) and saturated aliphatic acids near the downfield end (—185 5). The acidic -COOH proton normally absorbs as a singlet near 12 8 in the H NMR spectrum. As with alcohols (Section 17.12), the -COOH proton can be replaced by deuterium when D-jO is added to the sample tube, causing the absorption to disappear from the NMR spectrum. 

---