There are three reasons that suggest the former is not formed:The first Reason is average bond length, this is calculated that each c-c bond is in between the length expected of a c-c and a c=c bond suggesting that neither a double or single bond is formedSecond Reason is the reactivity shown by the C6H6 a molecule with alternate c-c and c=c bonds would normally undergo bromination however the molecule requires a catalyst suggesting that there are no c=c bonds present.C6H6 is much more stable than expected with the 1,3,5-Cyclohexatriene predicted structure with the enthalpy of hydrogenation is 150KJ less than expected. All this suggests that a more stable molecule is formed, this is benzene due to the stabilizing pi bonding above and below the molecule