Weakly nucleophilic leaving groups. Solvolyses of 1-adamantyl and t-butyl heptafluorobutyrates and trifluoroacetates

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Abstract
Kinetic data are reported for solvolyses of 1-adamantyl and t-butyl heptafluorobutyrates and trifluoroacetates in binary aqueous mixtures with acetone, ethanol, and methanol and in 97% trifluoroethanol–water and hexafluoropropan-2–ol-water. Logarithms of solvolysis rates for t-butyl heptafluorobutyrate compared with t-butyl chloride (Figure 3) and with 1-adamantyl heptafluorobutyrate (Figure 4) show the relatively low reactivity of solvolyses of t-butyl heptafluorobutyrate in fluorinated alcohols, consistent with nucleophilic solvent assistance for solvolyses of t-butyl heptafluorobutyrate in the more nucleophilic solvents (e.g. aqueous methanol). In 97% hexafluoropropan-2-ol–water, 1-adamantyl heptafluorobutyrate solvolyses faster than t-butyl heptafluorobutyrate, supporting a recent prediction. Comparisons of relative rates of solvolyses of 1-adamantyl trifluoroacetate with those of 1-adamantyl chloride (Figure 2) and with YOTs(Figure 5) show the absence of substantial effects on relative rates due to electrophilic solvent assistance by fluorinated alcohols, other than those already included in the Y values. Solvolyses of triflates are anomalous in comparison with solvolyses involving other weakly nucleophilic leaving groups (perchlorate, trifluoroacetate, and heptafluorobutyrate).

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