Deuterium substitution definition

The structure of [TpBut]ZnH has been determined by x-ray diffraction, although the hydride ligand was not located (Fig. 38). However, definitive evidence for the presence of the hydride ligand is provided by NMR and IR spectroscopies. Specifically, the hydride resonance is observed at 8 5.36 ppm in the H NMR spectrum, and p(Zn-H) is observed as a strong absorption at 1770 cm-1 in the IR spectrum, which shifts to 1270 cm 1 (vhIpd = 1.39) upon deuterium substitution (Fig. 39). 

This reaction sequence was definitively shown by use of temperature programmed reaction spectroscopy ( 7) The key to the success of this method was that reaction (4) was the rate-limiting step, allowing positive identification of the CH30(a) intermediate by TPRS. Isotopic substitution with b0 and deuterium was used to identify steps (2) and (3). 

By this definition, ethanol is a prochiral molecule. The two methylene hydrogens are enantiotopic (Section 9-10C) and substituting each separately (with, say, one deuterium) leads to a pair of enantiomers ... 

I.IO per deuterium atom for the methyl carbon calculated from experiments I and 2 and 1 and 3, respectively. The ratio kjk2 differs from kjk by a small, but definite amount. From the ratio of alcohol to olefin product in the various experiments, one concludes that there is no D—CHg isotope effect in the substitution or elimination reaction. Then, if we make the plausible assumption that there is no D—CHg isotope effect in the substitution reaction, one calculates from the experimental data a value of 1.80 for the ratio of proton to deuteron loss in the elimination reaction. This value is calculated by neglecting a possible secondary isotope effect in the elimination reaction. 

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