Do general nucleophilicity scales exist?

Comprehensive nucleophilicity scales including pi-, n- and sigma-nucleophiles have been constructed using benzhydrylium ions and structurally related quinone methides as reference electrophiles. It is shown how the correlation (Eqn (1)) log k(20 degrees C) = s(E + N), where s and N are nucleophile-specific parameters and E is an electrophile-specific parameter, has recently been employed to characterize further classes of nucleophiles (phosphines, amines, isonitriles, trifluoromethanesulfonyl-substituted carbanions) and electrophiles (2-benzylideneindan-1,3-diones and benzylidenebarbituric acids). Practical applications of the reactivity parameters E, N and s for developing Friedel-Crafts alkylations in neutral alcoholic or aqueous solution and for characterizing nucleophilic organocatalysts will be discussed. Eventually, a new correlation equation will be presented, which includes Eqn (1), the Ritchie equation (nucleophilic additions to stabilized carbocations), and the Swain-Scott equation (nucleophilic substitutions of methyl halides) as special cases. Copyright (c) 2008 John Wiley & Sons, Ltd.