there is indeed a carbocation formed, but it is an intermediate and is not usually shown in reaction mechanism. when reacting something like ethene, there will always be a major product, there is no such thing as a minor product when reacting ethene as the molecule is pretty much symmetrical once the C=C bond has been broken however, when reacting say butan-2-ene, you can have a major and minor product as the more stable primary molecule will be formed rather than the more reactive secondary molecule (i think, it does certainly have something to with positional isomerism) chemistry is indeed good stuff! lol
Okay, I'm going to try again to convince you I'm right Not trying to be a jerk, but I do genuinely believe I'm correct about this. If a carbocation intermediate were formed, it would imply that a carbocation rearrangement could occur during a bromination reaction. This, however, is never seen. Further, if there were a carbocation formed in the reaction, we would not see strictly anti stereochemistry, and we would see the syn product being formed as well (in at least some amount). good page on the topic With bromination, Markovnikov's rule does not need to be applied, because there is not a carbocation formed. 2-butene would give only 1 product after bromination (excluding stereoisomers), but it is exactly the same with 1-butene (not the same product, but the same in that there is only 1 product formed), because of the bromonium formed, there is no chance for rearrangement.
I believe that Stanmanfoo is right in this case. As I remember it (and hope it's right ), the reaction process does not involve an intermediate carbocation. Are you sure that you are not thinking of hydrogen bromide's reaction with ethene? In that case, a carbocation is formed in an intermediate stage and bonds with the negative bromide ion that results from the broken H-Br bond. This does not occur with Br2, because that instead breaks and temporarily forms a bridged bromonium ion (the triangle) as opposed to the intermediate carbocation arrangement.
nope... im adament there is a carbocation intermediate formed! http://www.chemguide.co.uk/mechanisms/eladd/symbr2.html there we go and it looks like we're both right! lol you must have learnt the second mechanism, whereas our syllabus requires the first mechanism! depends which syllabus really! and what is required! i follow the first as its easier for me and thats what we've got to learn! lol
Sorry another vote for the bromonium ion here. If i remember correctly as A-level they tell you it goes via the carbocation, you get to uni and they say "Wrong! Here's something called a bromonium ion"
