Alkoxyalkyl and -Alkoxycarbonyl Radicals

The relative rates of oxyalkylation of 4-substituted pyridines by methoxy-methyl, CH3OCH2, and phenoxymethyl, PhOCH2, radicals are summarized in Table 28, which also gives for comparison the corresponding values obtained with 

The ff-t5Tpe ethoxycarbonyl radical is on the contrary less nucleophilic than the acetyl radical (Table 29) in this Ccise the unpaired electron occupies a hybrid orbital and the incipient positive charge in the transition state cannot be stabilized by the lone-pair electron of the alkoxy group, as with the alkoxyalkyl radical, so that only the inductive effect is working and a clean reduction of nucleophilicity is observed. The remarkable fact is therefore that the same substituent, an a-alkoxy group, produces opposite polar effects depending on the electronic configuration of the carbon-centered radical. 

The strength of the bonds formed can also contribute to this behavior the alkoxy group increases the stability of the alkyl radicals by the resonance structures [Eq. (14)], decreasing therefore the strength of the bonds formed that should not occur in the alkoxy carbonyl radicals owing to their different configuration. 

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