Synthetic and structural studies of 1-halo-8-(alkylchalcogeno)naphthalene derivatives

A series of eight 1-halo-8-(alkylchalcogeno)naphthalene derivatives (1–8; halogen=Br, I; alkylchalcogen=SEt, SPh, SePh, TePh) containing a halogen and a chalcogen atom occupying the peri positions have been prepared and fully characterised by using X-ray crystallography, multinuclear NMR spectroscopy, IR spectroscopy and MS. Naphthalene distortion due to non-covalent substituent interactions was studied as a function of the bulk of the interacting chalcogen atoms and the size and nature of the alkyl group attached to them. X-ray data for 1, 2, 4 and 5–8 were compared. Molecular structures were analysed in terms of naphthalene ring torsions, peri-atom displacement, splay angle magnitude, X⋅⋅⋅E interactions, aromatic ring orientations and quasi-linear X⋅⋅⋅EC arrangements. A general increase in the X⋅⋅⋅E distance was observed for molecules that contain bulkier atoms at the peri positions. The I⋅⋅⋅S distance of 4 is comparable with the I⋅⋅⋅Te distance of 8, and is ascribed to a stronger lone pair–lone pair repulsion due to the presence of an axial S(naphthyl) ring conformation. Density functional theory (B3LYP) calculations performed on 5–8 revealed Wiberg bond index values of 0.05–0.08, which indicate minor interactions taking place between the non-bonded atoms in these compounds.