The geometry and electronic structure of exotricyclo[ 220.127.116.11(2,4)]oct-6-ene (exo-TCO) was investigated using DFT methods. The two faces of the endopyramidalised double bond of the molecule are not equivalent. The exo face of the double bond has regions with high electron density (q(i,HOMO)) and greater negative potential. Molecular complexes of exo-TCO with bromine were investigated using the B3LYP/6-311++ G(d, p) method; the exo-TCO center dot center dot center dot Br-2(exo) molecular complex was found to be relatively more stable than the exo-TCO center dot center dot center dot Br-2(endo) complex. The cationic intermediates of the reaction were studied by DFT and MP2 methods. The solvent effect was evaluated using the self-consistent isodensity polarised continuum model (SCI-PCM). The exo-bromonium cation was found to be more stable than the endo-bromonium cation. Exo-facial selectivity due to electronic and steric factors was observed upon addition of bromine to exoTCO. The multicentre nonclassical delocalised bromocarbonium cation IV and the exo-bridged-bromonium cation I are more stable than the rearrangement cation V. The reaction products are formed via exo-bridged-bromonium I and nonclassical IV cations, which are the most stable intermediates and whose stabilities barely differ. The mechanism of the addition reaction is also discussed.