Perhaps the most controversial and rare aspect of the halogen bonding interaction is the potential of fluorine in compounds to serve as a halogen bond donor. In this note, we provide clear and convincing examples of hypothetical molecules in which fluorine is strongly halogen bonding in a metastable state. Of particular note is a polycyclic system inspired by Selectfluor, which has been controversially proposed to engage in halogen bonding.

Molecular acid–base properties are core to understanding chemical systems and the prediction of reactivity. This axiom holds for cyclopropenium ions in terms of their broad use as (organo)­catalysts, ligands, redox-flow batteries, and applications in materials sciences. In view of this significant status, and with it, the critical importance of acidity, we disclose in this report the first comprehensive computational study of the pK a values of cyclopropenium ions employing a subset of 70 structurally diverse cyclopropenium derivatives, density functional computations, and Hammett linear free-energy relationships. Capitalizing upon these computed findings, and with an eye toward greenhouse gas trapping, we further document the timely use of a cyclopropenium–cyclopropenylidene coupled platform for CO2 capture and light-triggered release.

We report a detailed experimental and theoretical analysis of through‐space arene activation with halogens, tetrazoles and achiral esters and amides. Contrary to previously assumed direct activation through σ‐complex stabilization, our results suggest that these reactions proceed by a relay mechanism wherein the lone pair‐containing activators form exothermic π‐complexes with electrophilic nitronium ion before transferring it to the probe ring through low barrier transition states. Noncovalent interactions (NCI) plots and Quantum Theory of Atoms in Molecules (QTAIM) analyses depict favorable interactions between the Lewis base (LB) and the nitronium ion in the precomplexes and the transition states, suggesting directing group participation throughout the mechanism. The regioselectivity of substitution also comports with a relay mechanism. In all, these data pave the way for an alternate platform of electrophilic aromatic substitution (EAS) reactions.

We have found that face-to-face π-stacked aromatic rings show the propensity to activate one another toward electrophilic aromatic substitution through direct influence of the probe aromatic ring by the adjacent stacked ring, rather than through the formation of relay or "sandwich complexes." This activation remains in force even when one of the rings is deactivated through nitration. The resulting dinitrated products are shown to crystallize in an extended parallel offset stacked form, in stark contrast to the substrate.