why is benzine less reactive than cyclohexene there's still six carbons but there's one single double bond in cyclohexene in there three double bonds or at least the structure implies it in benzene the reason is that benzene has what we call resonance structures when you have a six membered ring an alternating double bonds how do you know which carbons those double bonds are alternating between if I drew you this hexagon with the other bonds having been double bonded how do you know that that's not the case well you don't and in fact these electrons are what's called a D localized none of these bonds are single and double in fact they're all about one and a half which is the average between the single bond that say this is in this resonance structure and the double bond that it is in the other resonance structure the average between one and two is 1.5 so if you look at the actual structure for benzene with like I don't know an electron microscope or something you'll find that all the bonds are the same length meaning there's no singles and doubles they're all one and a half the electrons themselves are not in one particular place they could be distributed around the entire ring that's what we mean by D localized they are not in one location they could be in many locations and I like to think of those electrons as smeared around the whole ring whereas in cyclohexene there are no resonance structures there are hydrogen's on these double singer like two single bonded carbons that's true here and here there are single hydrogen's here and here there are nowhere else for these electrons to go these are what we call localized very few organic chemistry teachers will call them localized but it is the opposite of delocalized it's in a fixed position and those two electrons are stuck there so if you brought these molecules in the of say BR - the BR 2's are going to be less like the electrons within the BR 2 bond are going to be less repelled by these electrons because they had no fixed location in the first place over here the BR twos approached the electrons you know are in this location and so the electrons in the BR bond are going to be repelled away that's the effect of London forces and that's why cyclohexene will react with BR 2 but in order for benzene to react with BR 2 you need a catalyst which lowers the activation energy cool the reason benzene is less reactive than cyclohexene is because the electrons here are delocalized so it's tougher for any particular molecule or for those electrons themselves to make an attack that will cause a reaction localized electrons you know where they are and so they can make a coordinated attack cool cool I hope that made sense best of luck