Nucleophilic substitution—continued table

TABLE 8.1 Functional Group Transformation via Nucleophilic Substitution [Continued)... 

TABLE 8.1 Representative Functional Group Transformations by Nucleophilic Substitution Reactions of Alkyl Halides Continued)... 

The more substituted radicals continue to be measurably the more nucleophilic. The relative rates with which the various alkyl radicals react with the 4-cyan-opyridinium cation (7.33, Y = CN) and the 4-methoxypyridinium cation (7.33, Y = OMe) are given in Table 7.2. The LUMO of the former will obviously be lower than that of the latter. The most selective radical is the ferf-butyl, which reacts 350000 times more rapidly with the cyano compound than with the methoxy. This is because the ferf-butyl radical has the highest-energy SOMO, which interacts (B in Fig. 7.4) very well with the LUMO of the 4-cyanopyridi-nium ion, and not nearly so well (A) with the LUMO of the 4-methoxypyridinium ion. At the other end of the scale, the methyl radical has the lowest-energy SOMO, and hence the difference between the interactions C and D in Fig. 7.4 is not so great as for the corresponding interactions (A and B) of the ferf-butyl radical. Therefore, it is the least selective radical, reacting only 50 times more rapidly with the cyano compound than with the methoxy. 

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