Reactions at Saturated Carbon

The Sn2 direct displacement reaction at saturated carbon can be represented as Y + R3CX R3CY + X ... 

We consider first the Sn2 type of process. (In some important Sn2 reactions the solvent may function as the nucleophile. We will treat solvent nucleophilicity as a separate topic in Chapter 8.) Basicity toward the proton, that is, the pKa of the conjugate acid of the nucleophile, has been found to be less successful as a model property for reactions at saturated carbon than for nucleophilic acyl transfers, although basicity must have some relationship to nucleophilicity. Bordwell et al. have demonstrated very satisfactory Brjinsted-type plots for nucleophilic displacements at saturated carbon when the basicities and reactivities are measured in polar aprotic solvents like dimethylsulfoxide. The problem of establishing such simple correlations in hydroxylic solvents lies in the varying solvation stabilization within a reaction series in H-bond donor solvents. 

Glukhovtsev, M. N., Bach, R. D., Pross, A., Radom, L., 1996, The Performance of B3-LYP Density Functional Theory in Describing SN2 Reactions at Saturated Carbon , Chem. Phys. Lett., 260, 558. 

For reaction of benzoyl chlorides in water, reactivity follows the electronreleasing ability of p-substituents, and there are striking differences in the micellar effects (Table 7). With electron-withdrawing substituents k+/k > 1, but its value progressively decreases with increasing electron release from a p-substituent. Thus an increase in electron release changes k+/k from values characteristic of a carbonyl addition reaction to values characteristic of SN reactions at saturated carbon. This classification also... 

In a series of recent papers, Komblum et at. have systematically investigated various factors of the reaction at saturated carbon, namely, the stereochemistry (Kornblum and Wade, 1987), the effect of light (Wade et ai, 1987), the effect of leaving groups (Kornblum et al., 1988) and the particular reactivity of the p-nitrocumyl system (Kornblum et al, 1987) as well as the conditions under which the cyano-group may replace the nitro-substituent in reactions involving a benzylic carbon (Kornblum and Fifold, 1989). 

Streitwieser, A, jr. Solvolytic displacement reactions at saturated carbon atoms. Chem. Reviews 56, 675 (1956). 

A. Streitwieser, Solvolytic Displacement Reactions at Saturated Carbon Atoms," Chem. Rev. 56, 571 (1956). 

Reactions at Saturated Carbons trans ting junction as the new formed bond would be pseudoequatorial. The five-membered ring D is produced because the resonance-stabilized benzyl cation 240 is formed in preference to the six-membered ring homobenzylic cation 241. 

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