The rac- and meso- forms of “all carbon” 1,2-diphosphonium dications with the naphthalene -1,8-diyl backbone were synthesised in good yields and purity by double alkylation of the parent diphosphine (1,2-diphenyl-1,2-diphosphaacenaphthene) using strong alkylating agents. Pure rac- and meso- forms of 1,2-diphosphoniums were obtained diastereospecifically by using methyl triflate and trimethyloxonium tetrafluoroborate respectively. It was found that the equilibrium between the rac- and meso- forms at room temperature in acetonitrile solutions effectively depends on the anion present. A reaction mechanism which proceeds via a P-pentacoordinated intermediate was proposed for the epimerisation observed between the rac- and meso- forms in the presence of F⁻ donors in the solution. Reactivity of the new 1,2-dications towards a range of compounds (nucleophiles, bases) was examined and a series of new compounds including phosphine-phosphoniums and phosphonium-phosphine oxides were obtained. Cyclic and acyclic compounds belonging to a novel group of phosphine-arsine mixed peri-substituted acenaphthenes were synthesised by introducing arsenic and phosphorus to the acenaphthene ring, using stepwise lithiation and carbon-group 15 element coupling. All new compounds were fully characterised including single crystal X-ray diffraction. The effect of the peri-substitution by phosphorus moieties and mixed arsine-phosphine peri-substitution on the naphthalene ring was studied using the detailed structural data obtained for these systems.