Isocyano group, electronic effects

Electronic effects of cyano, isocyano, acetylenic and diazonio groups... 

In a short section the electronic effect of the isocyano group is discussed. The possibility of including unipolar substituents in Hammett and similar treatments has long been a matter of controversy and this problem is discussed with special reference to the N2 substituent. The effects of acetylenic groups are examined in some detail and various unsatisfactory aspects are uncovered. Multiparameter treatments such as the Yukawa-Tsuno equation and the dual substituent-parameter equation have long been important and further treatments have been devised in recent years. A final section is devoted to some of these, with an indication of the place of CN, and to a lesser extent of the other groups of interest, in these treatments. 

An isocyano group can serve as both a protecting group for the amino function, and, due to its electronic effect, as an activating group as well. These two functionalities are employed in a synthetic route whereby an amino function has to be protected and a condensation reaction is performed at the a-carbon atom, for which activation is required [1185-1187]. 

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