Mercuration activation barriers

The linear free enogy relationship obsoved for arene donors relates the activation barrier AG for aromatic substitution directly to the CT transiticxi oiergy Aver of the EDA complex. Since Aver pertains to the energetics of the photoionizadons in equations (27) and (28), the correlation suggests that these arene contact ion pairs ate reasonable approximatims to the transition states for both mercuration and thallation, e.g. Scheme 6. 

Once inhaled, mercury vapour is relatively lipid soluble and crosses the lung alveoli into the bloodstream and red blood cells. Here, it is largely converted to an inorganic divalent (mercuric, Hg ) form by the enzyme catalase which is present in the red blood cells. However, small amounts of non-oxidised elemental mercury continue to persist and readily cross the blood/brain barrier into the central nervous system, where toxic effects are caused. These may reflect the subsequent conversion of mercury into ionised forms which are then trapped in the tissues. The characteristic symptoms are of tremor, especially in activities requiring fine... 

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