σ-Hole•••π and lone pair•••π interactions in benzylic halides

Intermolecular and intramolecular halogen center dot center dot center dot pi interactions in benzylic halides (Ph-CR2-X; X = F, Cl, Br and I) derived from 7-phenylnorbornane were investigated. The imposed geometry of the 7-arylnorbornane moiety prevents the participation of intramolecular attractive interactions between the sigma-hole region of the halogen atom and the pi electrons of the aromatic ring. Crystallographic data show intermolecular halogen bonds in iodide 1 and bromide 2 in the solid state. On the other hand, both UV-Vis and D-NMR data suggest the occurrence of intramolecular interactions between the halogen atoms and the phenyl rings in these compounds in solution. To provide more insight into the nature of the observed stabilizing interactions, density functional calculations were also carried out. These computations confirm the presence of genuine lone pair center dot center dot center dot pi intramolecular interactions which strongly affect the stability and the electronic structure of these species.