Arrangement of σ-Holes at Halogen Atom in Halonium Cation

Abstract

The halonium cations are important entities as they can be responsible for maintaining transition states during the organocatalysis. The distribution of the electrostatic potential on the crystal structures and theoretical models was investigated in the current study. The CSD survey revealed 478 structures of the [L···X···L]+ (X – any halogen atom, L - ligands attached to halogen) structural motif which were divided with respect to the values of the L···X···L angles. The value of this angle determined the number of σ-holes at halonium cation and hence the ability to its accommodate to the nucleophilic attack. The complexation with HCN as the Lewis base exhibited that one or two such ligands can be attracted depending on the number of σ-holes. The further study on the electrostatic potential apportionment on the surface on the model halonium [HF2C2-X-C2F2H]+ cations showed that altering the values of C···X···C angles led to following consequences: two σ-holes can be fused into one of the belt-like shape or both may disappear. The unusual fluctuations in the distribution of σ-holes caused by such geometry maneuvering were observed.