Rate constants for the reactions of dialkyl chalcogenides with laser flash photolytically generated benzhydrylium ions have been measured photometrically to integrate them into the comprehensive benzhydrylium-based nucleophilicity scale. Combining these rate constants with the previously reported equilibrium constants for the same reactions provided the corresponding Marcus intrinsic barriers and made it possible to quantify the leaving group abilities (nucleofugalities) of dialkyl sulfides and dimethyl selenide. Due to the low intrinsic barriers, dialkyl chalcogenides are fairly strong nucleophiles (comparable to pyridine and Nmethylimidazole) as well as good nucleofuges; this makes them useful group-transfer reagents.

The nucleophilic reactivities of substituted thiophenolates were determined by following the kinetics of their reactions with a series of quinone methides (reference electrophiles) in DMSO at 20 °C. The experimentally determined second-order rate constants were analyzed according to the Mayr− Patz equation log k = s N (N + E) to derive the nucleophile-specific reactivity parameters N and s N for ten thiophenolate ions.

The kinetics of the ring-opening reactions of thiophenolates with geminal bis(acceptor)-substituted cyclopropanes in DMSO at 20 °C was monitored by photometric methods. The determined second-order rate constants of the S N 2 reactions followed linear relationships with Mayr nucleophilicity parameters (N/s N ) and Brønsted basicities (pK aH ) of the thiophenolates as well as with Hammett substituent parameters (σ) for groups attached to the thiophenolates. Phenyl-substituted cyclopropanes reacted by up to a factor of 15 faster than their unsubstituted analogues, in accord with the known activating effect of adjacent π-systems in S N 2 reactions. Variation of the electronic properties of substituents at the phenyl groups of the cyclopropanes gave rise to parabolic Hammett relationships. Thus, the inherent S N 2 reactivity of electrophilic cyclopropanes is activated by electron-rich π-systems because of the more advanced C1À C2 bond polarization in the transition state. On the other hand, electron-poor π-systems also lower the energetic barriers for the attack of anionic nucleophiles owing to attractive electrostatic interactions.

The kinetics of ring‐opening reactions with thiophenolates in DMSO were monitored to assess the inherent SN2 reactivity of electrophilic cyclopropanes. Phenyl‐substituted cyclopropanes reacted faster than their unsubstituted analogues. Variation in the electronic properties of substituents at the phenyl groups of the indandione‐derived cyclopropanes gave rise to parabolic Hammett relationships, which revealed variable electrophile‐dependent effects on the stabilization of the transition states. More information can be found in the Full Paper by A. R. Ofial et al. (DOI: 10.1002/chem.202103027). Artwork by A.S.

The dynamics of the allylic rearrangement of the (1,3‐diphenylallyl)dimethylsulfonium ion in CD2Cl2, which proceeds via intermediate 1,3‐diphenylallyl cations, has been investigated by variable temperature 1H NMR spectroscopy. At low temperature, the three allylic protons give rise to an AMX system, and the two diastereotopic S‐methyl groups resonate at different frequencies. At higher temperature, an AX2 system for the allylic protons and a single signal for the S‐methyl groups are observed. The resulting exchange rate constant of (364 ± 2) s–1 at 25°C, which corresponds to the rate of the heterolytic cleavage of the C–S bond, was used to explore the range of validity of the linear free energy relationship log khet(25°C) = sf (Nf + Ef), which describes the rates of heterolytic cleavages by the electrofugality parameter Ef and the solvent‐dependent nucleofuge‐specific parameters Nf and sf. The observed rate constant corroborates a previous conclusion that two different sets of Nf and sf parameters may exist for the same nucleofuge. Knowledge of whether the reverse bond‐forming reaction occurs under activation or under diffusion control is crucial for the choice of the appropriate set of nucleofugality parameters.