Qualitative nucleophilicity scale, reactions

We tried to construct a qualitative nucleophilicity scale by combining the data for the three main systems of Table X and addition of the other data from the short reaction series. In most cases, the relationship between a nucleophile from the main series and only one of the nucleophiles in the short series is known. Hence, our combined nucleophilic scale is given in Figure 1 in the form of two lines. The main one (in boldface type) is a single reactivity scale, whereas short series are introduced above in the appropriate places (other orders are HOO- > CIO- and FC-(N02)2 > RC-(N02)2 where... 

From this discussion, clearly, a quantitative nucleophilicity scale toward vinylic carbon cannot be constructed. Neither Ritchies nor Swain-Scott s correlations are applicable. Different blends of contribution of polar, steric, and symbiotic effect can change the reactivity order. Whether a qualitative order prevails could be inferred by comparing the three substitution reactions of chloro olefins, which are the only processes for which a relatively extensive change in the type of nucleophile was conducted (Table X). 

Some typical values of /ip, are Cl" (3.04) NH3 (3.07) Nj" (3.58), r (5.46) CN (7.14) PPhj (8.93). Clearly, if one is testing for entering group effects in Pt(II) chemistry, one should not choose Cl and NH3 as test nucleophiles because their nucleophilicities are almost identical and one would not see much entering or leaving group effect This scale wotks well for Pt(II) reactions, but is at best a qualitative indicator for other metals and not even that for the fust-row transition-metal ions. 

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