High‐Fidelity Dimerization of Xanthenyl Radicals and Dynamic Qualities of a Congested Ethane: Diethyl Dixanthenyl‐9,9′‐Dicarboxylate

Abstract

Exploration of the sterically‐congested ethane diethyl dixanthenyl‐9,9′‐dicarboxylate has revealed the dynamic behavior arising from its congested C−C bond. Interlocking ‘geared’ substituents and favorable dispersion interactions around this bond result in a conformational preference for partially cofacial xanthene moieties both in solid state and as dilute solutions. The weak, centrally located C−C bond is 1.628 Å long and permits selective thermolysis to yield two carbon‐centered ethyl xanthenyl‐9‐carboxylate radicals, which dimerize with high fidelity into the original sterically‐congested ethane. Recombination of the radicals into this symmetrical head‐to‐head dimer is highly reproducible – by observing the equilibrium, the bond dissociation enthalpy was calculated to be 20.4 kcal ⋅ mol−1. The substituents around the central carbon provide insufficient stabilization against oxygen, which consumes the radicals and unbalances the dimer‐radical equilibrium.

Theoretical and Experimental Investigations of Stable Arylfluorene‐Based Radical‐Type Mechanophores

“…This information will not only be pertinent for the design of novel mechanoresponsive materials, but also further the understanding of related organic and polymer chemistry based on radical species. [42][43][44][45][46][47][48][49][50]…”

“…The purpose of this study was thus to reveal the effect that particularly electron‐withdrawing substituents have on the reactivity of carbon‐centered radicals generated from RMs toward aerobic oxygen. This information will not only be pertinent for the design of novel mechanoresponsive materials, but also further the understanding of related organic and polymer chemistry based on radical species [42–50] …”