Intra- versus intermolecular electron transfer in radical nucleophilic aromatic substitution of dihalo(hetero)arenes – a tool for estimating π-conjugation in aromatic systems† †Electronic supplementary information (ESI) available: Experimental details and procedures, 1H and 13C NMR data, GC traces and mass spectra. CCDC 1526301 and 1526302. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc00100b Click here for additional data file. Click here for additional data file.

In this paper, the application of the double radical nucleophilic aromatic substitution (SRN1) in various dihalogenated, mostly diiodinated, p-conjugated systems as a tool for qualitatively estimating their pconjugation is described. This approach uses electron delocalisation as a measure of p-conjugation. Electron injection into the p-system is achieved via reaction of an intermediate aryl radical, itself generated from a dihalogenated p-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 arylhalogen moiety within the p-system via an intramolecular electron transfer process. The efficiency of this intramolecular electron transfer is related to the p-conjugation of the radical anion. If the pconjugation 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 SRN1 substitution whereas the intermolecular ET pathway provides a product of a monoSRN1 substitution. By simple product analysis of monoversus double substitution, p-conjugation can be qualitatively evaluated. This mechanistic tool is applied to various dihalogenated p-conjugated systems and the results are discussed within the context of p-conjugation. The conjugation mode within the p-system and the length of the aromatic system are varied, and the effect of relative positioning of the two halides within small psystems is also addressed.