Isotope Effects

Two effects of replacing hydrogen by deuterium have already been seen. The first concerns volatility. The C-D bond is shorter than the C-H bond, so that deuterated compounds are slightly more volatile and elute towards the front edge of a gas chromatographic peak. The methyl ester of fully deuterated stearic acid elutes as a separate peak before normal methyl stearate. The second example arises in NMR spectroscopy. Not only do 'H and 2H resonate at different radio-frequencies and have different numbers of spin states, but 13C attached to 2H has a slightly different chemical shift from 13C attached to 'H (Figure 5.9(c)). Many other isotope effects could be mentioned. It is curious to discover that D20 does not support animal or plant life because of the small differences in bond energies.

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