Synthetic and structural studies of 1,8-chalcogen naphthalene derivatives

Four novel 1,8-disubstituted naphthalene derivatives 4-7 that contain chalcogen atoms occupying the peri positions have been prepared and fully characterised by using X-ray crystallography, multinuclear NMR spectroscopy, IR spectroscopy and MS. Molecular distortion due to noncovalent substituent interactions was studied as a function of the bulk of the interacting chalcoeen atoms and the size and nature of the alkyl group attached to them. X-ray data for 4-7 was compared to the series of known 1,8-bis-(phenylchalcogeno)naphthalenes 1-3, which were themselves prepared from novel synthetic routes. A general increase in the E center dot center dot center dot E' distance was observed for molecules containing bulkier atoms at the peri positions. The decreased S center dot center dot center dot S distance from phenyl-1 and ethy1-4 analogues is ascribed to a weaker chalcogen lone pair lone pair repulsion acting in the ethyl analogue due to the presence of two equatorial S(naphthyl) ring conformations. Two novel pen-substituted naphthalene sulf-oxides of 1, Nap(O=SPh)(SPh) 8 and Nap(O=SPh), 9, which contain different valence states of sulfur, were prepared and fully characterised by using X-ray crystallography and multinuclear NMR spectroscopy, ER spectroscopy and MS. Molecular structures were analysed by using naphthalene ring torsions, pen-atom displacement, splay angle magnitude, 5 center dot center dot center dot 5 interactions, aromatic ring orientations and quasi-linear O=S center dot center dot center dot S arrangements. The axial S(naphthyl) rings in 8 and 9 are unfavourable for SS contacts due to stronger chalcogen lone pair lone pair repulsion. Although quasi-linear O=S center dot center dot center dot S alignments suggest attractive interaction is conceivable, analysis of the B3LYP wavefunctions affords no evidence for direct bonding interactions between the S atoms.