Hydrogenation of an aromatic ring

Reactions in which a metal replaces the hydrogen of an aromatic ring are considered along with their aliphatic counterparts in Chapter 12 (12-20 and 12-21). 

Rate constants such as kD represent rate constants involving sulfur removal from molecules, and rate constants such as kw> and km represent rate constants involving hydrogenation of an aromatic ring. The subscripts 0, 1, and 2 indicate that, for the desulfurization process, the product is a... 

It is more doubtful whether a nitrate radical would attack at a ring hydrogen of an aromatic ring and thus start a sequence leading to the (admittedly not positively identified) aryl nitrate, since aryl radicals would be very difficult to oxidize to aryl cations. On the other hand, it is not possible to formulate a reasonable direct mechanism for the formation of propyl nitrate from propene. Thus, a blend of mechanisms may operate, as indeed was concluded earlier (Nyberg, 1970 Ross et al., 1972). 

You are trying to find out whether or not there is an isotope eflect in a particular kind of substitution in w hich the electrophile Y replaces a hydrogen of an aromatic ring. In each of the following cases, tell what you would do, and what you would expect to observe if there were an isotope effect. (You can quantitatively analyze mixtures of isomers. Your mass spectrometer will tell you what percentage of the hydrogen in a compound is deuterium, but not the location of deuterium in a molecule.)... 

Electrophilic aromatic substitution Fundamental reaction type exhibited by aromatic compounds. An electrophilic species (E ) replaces one of the hydrogens of an aromatic ring. 

In this section, we study several types of electrophilic aromatic substitution reactions—that is, reactions in which a hydrogen of an aromatic ring is replaced by an electrophile, E. The mechanisms of these reactions are actually very similar. In fact, they can be broken down into three common steps ... 

An electrophilic aromatic substitution in which a hydrogen of an aromatic ring is replaced by an alkyl or acyl group. 

Orthometallation refers specifically to the substitution of orfho-hydrogens of an aromatic ring of a ligand by a metal atom and is a specific type of cyclometallation, e.g.. Scheme 12.12 ... 

---