Intra- versus intermolecular electron transfer in radical nucleophilic aromatic substitution of dihalo(hetero)arenes - a tool for estimating ?-conjugation in aromatic systems.

ABSTRACT: In this paper, the application of the double radical nucleophilic aromatic substitution (S_RN1) in various dihalogenated, mostly diiodinated, ?-conjugated systems as a tool for qualitatively estimating their ?-conjugation is described. This approach uses electron delocalisation as a measure of ?-conjugation. Electron injection into the ?-system is achieved via reaction of an intermediate aryl radical, itself generated from a dihalogenated ?-system via SET-reduction of the C-I bond and subsequent reaction with a thiolate anion. The generated arene radical anion can then further react with the second aryl-halogen moiety within the ?-system via an intramolecular electron transfer process. The efficiency of this intramolecular electron transfer is related to the ?-conjugation of the radical anion. If the ?-conjugation within the aromatic unit is weak, the arene radical anion reacts via an intermolecular ET with the starting dihalide. The intramolecular ET process delivers a product of a double S_RN1 substitution whereas the intermolecular ET pathway provides a product of a mono- S_RN1 substitution. By simple product analysis of mono- versus double substitution, ?-conjugation can be qualitatively evaluated. This mechanistic tool is applied to various dihalogenated ?-conjugated systems and the results are discussed within the context of ?-conjugation. The conjugation mode within the ?-system and the length of the aromatic system are varied, and the effect of relative positioning of the two halides within small ?-systems is also addressed.

SUBMITTER: Janhsen B 

PROVIDER: S-EPMC5436300 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature