Grunwald

Leffler J E and Grunwald E 1963 Rates and Equilibria in Organic Reactions (New York Wiley)... 

Aniline hydrobromide [542-11-0] M 174.0, m 286". Crystd from water or EtOH and dried at 5mm over P2O5. Crystd four times from MeOH containing a few drops of cone HCl by addition of pet ether (b 60-70°), then dried to constant weight over paraffin chips, under vacuum [Gutbezahl and Grunwald J Am Chem Soc 75 559 795i]. It was ppted from EtOH soln by addition of Et20, and the filtered solid was recrystd from EtOH and dried in vacuo. [Buchanan et al. J Am Chem Soc 108 1537 1986.]... 

We have seen that 10" M s is about the fastest second-order rate constant that we might expect to measure this corresponds to a lifetime of about 10 " s at unit reactant concentration. Yet there is evidence, discussed by Grunwald, that certain proton transfers have lifetimes of the order 10 s. These ultrafast reactions are believed to take place via quantum mechanical tunneling through the energy barrier. This phenomenon will only be significant for very small particles, such as protons and electrons. 

For tbe rate of proton transfer between the lyonium ion (MeOH2 ) and solvent (MeOH) and the lyate ion (MeO ) and solvent, Grunwald et al. give this result ... 

Figure 5-24. The u.v and x,y coordinate systems of Grunwald s analysis of the RIP diagram. The u.v coordinates are in parentheses and the jr,y coordinates are in brackets.

Grunwald has shown applications of Eqs. (5-78) and (5-79) as tests of the theory and as mechanistic criteria. One way to do this, for a reaction series, is to estimate AG° and AG from thermodynamic data and from reasonable approximations and then to fit experimental rate data (AG values) to Eq. (5-78) by nonlinear regression. This yields estimates of AGq and AG (which are constants within the reaction series), and these are then used in Eq. (5-79) to obtain the transition state coordinates. 

Though LFERs are not a necessary consequence of thermodynamics, their occurrence suggests the presence of a real connection between the correlated quantities, and the nature of this connection can be explored. This treatment follows Leffler and Grunwald. - PP Standard free energy changes AG° will pertain to either... 

The literature in this area is extensive and some of the concepts and symbolism may be transitory. This chapter reviews the field at a level and with a coverage adequate for the experimentalist to use the standard relationships and to follow their use in the mechanistic literature. Research on the meaning of the extrathermody-namic relationships themselves is beyond our needs the interested reader can explore these ideas further in the references cited. Grunwald has reviewed the early history of LFERs. 

Consider a bimolecular reaction between a substrate and a reagent. Upon each encounter of these two species there is a probability P that reaction will occur. If the solution contains two substrates Sj and S2, each characterized by a probability of reaction P, and P2 with the common reagent, evidently the ratio P2lP is a measure of the selectivity of this process for S2 relative to S,. If the two substrates are not markedly dissimilar, the ratio P2IP1 will be similar to the ratio of rate constants, 2/ 1- Leffler and Grunwald pp define the selectivity as... 

The observed solvent effect can be expressed quantitatively with the aid of the Leffler-Grunwald operator 5m introduced in Chapter 7. For rate constant k measured in medium M we have, from transition state theory, k = (kT//i)exp ( —AGm// T) and similarly for rate constant ko measured in a reference solvent. Combining these two expressions gives... 

Univariate LSERs may possess the conventional LEER form, as exemplified by Eq. (8-67), the Grunwald-Winstein equation, or they may simply be plots of log k against a solvent parameter such as Z, (30), or ir. Brownstein developed an LEER form for the latter type of correlation, writing... 

J. E. Leffler and E. Grunwald Rates and Equilibria of Organic Reactions, Chapter 9. Wiley, New York, 1963. 

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