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In this paper we show how graphical analysis of ligand effect data for families of ligands should be combined with regression analysis in order to gain a more self-consistent interpretation of regression results. If a steric threshold shows up in the graphical analysis of the data for the trialkyl ligands (AR 3 ), then the threshold must show up in regression analysis of the full set of data. Similarly, the dependence of the data for the isosteric ligands A(p-XC 6 H 4 ) 3 must have the same dependence on the electronic parameter χ that we find for the regression analysis for the full set of data. Finally, graphical analysis for both AR 3 and A(p-XC 6 H 4 ) 3 families shows vividly whether steric effects and/or aryl effects belong in the full analysis. Thus, for results of any regression analysis to be acceptable, they must be consistent with the results of graphical analysis.

Through the quantitative analysis of ligand effects (QALE), we have probed π effects associated with Rh-P bond lengths, ν CO , and -∆H rx for Rh(CO)(Cl)(PX 3 ) 2 and ν CO and -∆H rx for Rh(acac)(CO)(PZ 3 ). It was found that π effects are complex and depend strongly on the nature of ancillary or other participatory groups. The results of the QALE analysis of -∆H rx point out the importance of synergistic interactions between PZ 3 and other ancillary ligands in accord with theoretical computations. Literature data for Rh(CO)(Cl)(PZ 3 ) 2 have been supplemented with new values of ∆H rx for PMe 3 (-75.6 ( 0.3 kcal/mol), P(i-Pr) 3 (-68.7 ( 0.3 kcal/mol), and PCy 3 (-66.4 ( 0.4 kcal/mol) as well as crystal structures for Rh(CO)(Cl)-(P(i-Pr 3 )) 2 (Rh-P ) 2.3488(3) Å) and Rh(CO)(Cl)(PCy 3 ) 2 (Rh-P ) 2.3508 (3)).

Using the QALE model, we determined the QALE stereoelectronic parameters for the following ligands:In addition, we evaluated the parameters for P. Revised parameters for PF 3 are also presented: χ d ) 33 ( 2, θ ) 110 ( 24°, E ar ) 0, π p ) 13.2 ( 0.5. The absence of an indicated error means that these values were assigned initially to the particular parameters in the analyses or that the parameters are statistically indistinguishable from zero. Where a comparison can be made, we find that our calculated values of θ are indistinguishable from those of Tolman; therefore, we suggest the continued use of Tolman's values. It is observed that the perfluoroalkyl groups are highly π acidifying and that this effect is transmitted through intervening CH 2 groups.