Ritchie equation

RITCHIE EQUATION ELECTROPHILE NUGLEOPHILIC GATALYSIS NUCLEOPHILIC COMPETITION NUCLEOPHILICITY ALPHA EFFECT ELECTROPHILICITY... 

MICROTUBULE ASSEMBLY KINETICS RITCHIE EQUATION RNA, exonucleolytic cleavage, PHOSPHODIESTERASES RNA LIGASE RNA POLYMERASES EDITING MECHANISMS REPLICASE RNA stability,... 

Fig. 2 A simplified version of Fig. I. The point A locates the transition states for systems obeying the Ritchie equation (11) for nucleophilic addition to R. Transition states for methyl transfer reactions occur in the shaded area...

See also electrophilicity Ritchie equation SWAIN-SCOTT EQUATION. 

Ritchie equation The linear free-energy relation log kN = log k0 + N+... 

The addition of nucleophiles to a carbenium ion (4-nitromalachite green, Equation 46) provides a useful reference reaction for nucleophilic attack. Parameters for nucleophiles (2V+) are defined by Equation (47) (the Ritchie equation) for reactions of nucleophile with malachite green and 4-nitromalachite green (see structures in Equation 46). N+ values are tabulated in Appendix 3, Table 4. 

Equation 7 is also related to the Ritchie equation 9, applied to nucleophile-electrophile bond-forming reactions. The formal similarity and the apparently unusual constant selectivity common to both suggest the possibility of a closer relation. However, our Nx values are in principle related to identity rates, which as pointed out by Ritchie et al. (23) do not exist for these one-bond-forming reactions and cannot be a part of his N+ values. 

This equation relates the nucleophilicity of a nucleophile with its rate constant in a given SN2 reaction. In this class of reactions, bond formation and bond cleavage are fused into a single transition state. A seemingly less complicated reaction is a reaction in which the status of only one bond is changed in the rate-determining step. Anion-cation combinations exemplify this type of reaction. The relationship between rate constants and nucleophilicity in these reactions is given by the Ritchie equation (2, 3) ... 

The two major differences between these two equations are as follows (1) Unlike the Swain-Scott equation, the Ritchie equation lacks a selectivity parameter. Thus, a plot of log k versus N+ always gives a unity slope. (2) Nucleophilicity ranking by the two scales is different. This difference is especially noticeable for the three nucleophiles, CN-, CH30-, and N3-. According to the N+ scale, the nucleophilicity order is N3- > CH30- > CN-, whereas the reverse is true for the Swain-Scott n scale. 

To test the generality of the Ritchie equation, we reacted the olefins 9-(dinitromethylene)fluorene (FDN), 9-(dicyanomethylene)fluorene (FDCN), and 9-(nitromethylene)fluorene (FN) with a series of nucleophiles (4, 5). The reaction of these three substrates resemble that of anion-cation combination reactions in the absence of leaving group departure at the transition state. Yet, in spite of the fact that these substrates are not positively charged, an excellent correlation was observed with the N+ scale. Similar results were observed for other uncharged substrates such as carbonyl functions (6) and activated aryl halides (7). However, the three systems, FDN, FDCN, and FN, are unique in that the slopes of log k versus N+ are significantly larger than 1. This necessitates the incorporation of a selectivity parameter (S+) into the Ritchie equation. 

Recently, we found (unpublished results) that the reactions of the diphenyl analogues of these three substrates do not follow the Ritchie equation and the data are highly scattered. One major difference between the two sets of substrates is the extent of steric crowding around the activated carbon. However, the mechanism by which the steric effect induces this change is not entirely clear. 

Ritchie (2) suggested that the differences between the reactions that follow the Swain-Scott and the Ritchie equations stem from the coupling between bond formation and bond cleavage in the SN2 process as opposed to only... 

This model may also be appropriate to other LL substrates, such as carbonyl groups (6), activated double bonds (5, 19), and aryl halides (7), that also obey the Ritchie equation. This seems appropriate because these LL substrates are highly polar and because particularly in solution the zwitterion I is a major contribution to their overall resonance structure ... 

One interesting aspect of equation 8.46 is that it can be shown to incorporate both the Ritchie equation (equation 8.21, page 479) and the Swain-Scott... 

In contrast to organic chemistry, where extensive studies have attempted to correlate nucleophilicity with various parameters (e.g., the Swain-Scott, Edwards, and Ritchie equations), there is currently little quantitative information concerning nucleophilic reactivities toward coordinated ir-hydrocarbons. Recent kinetic studies of reactions shown in equations (10) and (11) have established... 

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