Rates of Solvolysis of Phenyldimethylcarbinyl Chlorides Containing Meta Directing Substituents^1,2

[18F]-Organotrifluoroborates as Radioprosthetic Groups for PET Imaging: From Design Principles to Preclinical Applications

“…Hammett analysis of cumyl chloride solvolysis showed that electron-donating groups (EDGs) at the para position greatly accelerate solvolysis while electron-withdrawing groups (EWGs) retard solvolysis. 31 We therefore performed a Hammett analysis to quantify the effects of EDGs and EWGs in terms of published σ and σ + values; log(k solv ) is negatively correlated with the sum of the σ values: ρ ≈ −1 (R ≈ 0.9). 32 In addition, ortho substituents sterically clash with the fluorine atoms of difluoroborane 5, disfavoring its production and thereby retarding solvolysis of the trifluoroborate.…”

“…From the mechanism (Figure ), we drew an analogy between an sp 2 -hybridized boron and an sp 2 -hybridized carbocation (Figure ). Hammett analysis of cumyl chloride solvolysis showed that electron-donating groups (EDGs) at the para position greatly accelerate solvolysis while electron-withdrawing groups (EWGs) retard solvolysis . We therefore performed a Hammett analysis to quantify the effects of EDGs and EWGs in terms of published σ and σ + values; log­( k solv ) is negatively correlated with the sum of the σ values: ρ ≈ −1 ( R ≈ 0.9) .…”

From Minutes to Years: Predicting Organotrifluoroborate Solvolysis Rates

“…Perrin and co‐workers showed that at neutral pH or higher, aryltrifluoroborates solvolyze in a nearly pH‐independent manner whereby loss of the first fluorine atom is rate‐limiting and no mono‐/difluoroborate intermediate is detectable at relatively low concentrations of starting material, consistent with an irreversible reaction that is third‐order in fluoride (vide infra) 13. By analogy to cumyl chlorides,14 electron density from the π‐aryl system delocalizes into the empty p‐orbital on boron weakening the BF bond thereby facilitating fluoride ion expulsion. The resulting difluoroborane hydrates instantly and solvolyzes to completion.…”

A Practical Synthesis of para Di- and Mono-Substituted Benzhydrylamines from Benzhydrol Precursors

“…The most stabilized benzhydryl cations were rapidly formed in acetic acid containing a trace of sulfuric acid (Method A), due to the presence of electron-releasing substituents (OMe: s p = -0.27 and s p + = -0.78; Me: s p = -0.17 and s p + = -0.30). 38,39 These intermediates selectively reacted with the best nucleophile present in the medium, i.e. the carbamate 2; solvolysis products 4 corresponding to the reaction of acetic acid as the nucleophile were not found (X = X' = OMe), or were isolated in very small amounts (X = X' = Me).…”

“…the carbamate 2; solvolysis products 4 corresponding to the reaction of acetic acid as the nucleophile were not found (X = X' = OMe), or were isolated in very small amounts (X = X' = Me). The less stabilized benzhydryl cations bearing electron-withdrawing substituents (Cl : s p = 0.20 and s p + = 0.11; F : s p = 0.07 and s p + = -0.07) 38,39 were also formed in acetic acid, but due to their higher reactivity, they conducted mainly to the solvolysis products 4. This reaction could be partially or totally avoided by working either in a poorly nucleophilic acidic solvent such as trifluoroacetic acid (Method B), or in acetonitrile containing one equivalent of triflic acid (Method C).…”