Interplay between Structure and Mechanism in Reductive Dissociative Electron Transfers to α,β -Epoxyketones.

The electrochemical reduction of several α,β -epoxyketones was studied using cyclic (linear sweep) voltammetry, convolution voltammetry, and homogeneous redox catalysis. The results were reconciled to pertinent theories of electron transfer. α,β -Epoxyketones undergo dissociative electron-transfer reactions with C-O bond cleavage, via both stepwise and concerted mechanisms, depending on their structure.

Stereoelectronic and Resonance Effects on the Rate of Ring Opening of -Cyclopropyl-Based Single Electron Transfer Probes.

-Cyclopropyl--methylaniline () is a poor probe for single electron transfer (SET) because the corresponding radical cation undergoes cyclopropane ring opening with a rate constant of only 4.1 × 10 s, too slow to compete with other processes such as radical cation deprotonation. The sluggish rate of ring opening can be attributed to either (i) a resonance effect in which the spin and charge of the radical cation in the ring-closed form is delocalized into the phenyl ring, and/or (ii) the lowest energy conformation of the SET product () does not meet the stereoelectronic requirements for cyclopropane ring opening.

Does Metal Ion Complexation Make Radical Clocks Run Fast? An Experimental Perspective.

The rate constant for the β-scission of the cumyloxyl radical (k) was measured in the presence of various added electrolytes in acetonitrile and DMSO solvent. The results show that in CHCN, k increases in the presence of added electrolyte, roughly paralleling the size of the cation: Li > Mg ≈ Na > BuN > no added electrolyte. As suggested by Bietti et al.

Cyclopropyl conjugation and ketyl anions: when do things begin to fall apart?

Results pertaining to the electrochemical reduction of 1,2-diacetylcyclopropane (5), 1-acetyl-2-phenylcyclopropane (6), 1-acetyl-2-benzoylcyclopropane (7), and 1,2-dibenzoylcyclopropane (8) are reported. While 6*- exists as a discrete species, the barrier to ring opening is very small (<1 kcal/mol) and the rate constant for ring opening is >10(7) s(-1). For 7 and 8, the additional resonance stabilization afforded by the benzoyl moieties results in significantly lower rate constants for ring opening, on the order of 10(5)-10(6) s(-1).