the 5-position over that of the parent compound by coordination with cobalt(1n) cations. Studies are in progress to determine whether the difference in reactivity derives from reduction of the effective charge on the nitrogen or whether there is also an important degree of x-electron donation to the ring from the filled Co de orbitals.Phenazine 5-oxide undergoes nitration at the 3-(and to a minor extent the 1-) position; kinetic criteria show that the monocation (40) is the reactive speciesL331.[33] A . R. Katritzky and B. Swedlund, unpublished.
E. ConclusionVery much remains to be accomplished. On the experimental side it is necessary to gain quantitative data as to the effect on rate of substitution (by a wide variety of electrophiles) of the replacement of a CH-group by an uncharged nitrogen atom, by various types of group incorporating a partially charged nitrogen (N@H, Ne-00, N@-R,N@-OH, etc.), and by charged ==S@-or =O@-. Only when more is known of the effects of these replacements towards the ortho, meta, and para positions, as well as effects relayed from one ring to another, will it be possible to develop and test the theoretical treatments, and, hopefully, to gain a real understanding of the field.
Acetylcholinesterase plays a vifal part in the functioning of nerves, andseriousphysioIogica1 damage arises from its blockage by esters ofphosphonic andphosphoric acid used e.g. in pesticides. The properties and the mechanismof action of acetylcholinesterase, which show many similarities to those of other hydrolases, are described. Therapeutic agents (reactivators) for the toxic phosphorus compounds specified are also discussed. P. Schade' and D. H. Ford: Basic neurology, an introduction to the structure and function of the nervous system. Elsevier, Amsterdam-London-New York 1965 ; b) W. Blasius in Landois-Rosemann: Lehrbuch der Physiologiedes Menschen,
