Do resonance-assisted intramolecular halogen bonds exist without a charge transfer and a σ-hole?

Abstract

To analyze the properties and mechanisms of six types of intramolecular resonance-assisted halogen bonds (Br⋯O, Cl⋯O, F⋯O, Br⋯O, Cl⋯S and F⋯S), we have chosen the five-membered closed ring system X–C₁R₁= C₃R₂–C₂R₃= Y (X = Br, Cl & F; Y = O & S) of unsaturated compounds with the substituents NO₂, CH₃and H.