Full geometric optimization of bicyclo[3.2.2]nona-6,8-diene (BND) is done by ab initio and DFT methods and the structure of the molecule is also investigated. The double bond (1) situated in the opposite direction of methylene group in BND molecule is more exo pyramidalized than the other double bond (II). The electron density (q(i,HOMO)) of the double bond (1) in HOMO of the molecule is more than that of the double bond (II). Exo and endo faces of exo pyramidalized double bonds of the molecule are not equal and electron density is bigger in endo faces. The molecular complexes of BND with chlorine have been investigated by B3LYP/6-311+G* method and their stable configurations have been determined. The reason why endo molecular complexes are more stable than exo molecular complexes, can be explained by electronic and steric factors. Because of electronic factors, BND center dot center dot center dot Cl-2(endol) complex is more stable than BND center dot center dot center dot Cl-2(endo2). The endo-bridged chloroniuM cation (1) is relatively more stable than the endo-bridged cation (11). Endo-facial stereoselectivity and regioselectivity should be observed in the addition of chlorine to BNID molecule. Endo-facial stercoselectivity is caused by electronic and steric effects, and regioselectivity by electronic effects. The rearranged chlorocarbonium cation (IV) is the most stable among the cationic intermediates and the ionic addition reaction occurs via this cation.