Arenes, hydrogen-deuterium exchange

This may be contrasted with the D SO -promoted hydrogen-deuterium exchange at an arene (Eq. 1.1). In this case, the electrophilic chemistry occurs at the polarized deuterium-oxygen bond, where the deuterium atom carries a significant positive charge. Although the various S Ar synthetic reactions do share a common basic mechanism (Scheme 1.2), they often differ considerably in the means or mechanisms by which the electrophiles are generated. Several of the common mechanistic types are described below. 

Deuterium-hydrogen exchange in (CgHg)Cr(CO)3 and (MeCgHg)Cr-(CO)3 has been shown to take place in ethanol solution in the presence of sodium ethoxide, whereas no exchange is observed in the uncom-plexed arenes 265). 

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