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Markonikov's rule application?

Theres this question...2-methylbut-1-ene reacts with Hydrogen bromide to form either 1-bromo-2-methylbutane or 2-bromo-2-methylbutane, by electrophilic addition

At first i figured 1-bromo would be the major product and the hydrogen of the HBr would combine with the 2nd carbon, which has 3 hydrogens(from the methyl group) instead of the 1st carbon which has only 2 hydrogens bonded, based on markonikov's rule of the hydrogen binding with the carbon that already contains the most hydrogen..

But i checked and its actually 2-bromo-2-methylbutane which is the major product based on it being a tertiary carbocation, whereas 1-bromo is only a primary cation...tertiary is more stable than primary i get that.

So does markonikovs rule just not apply for this question

The final question of this is asking me to explain the reason for the products formed(for 3 marks)...so do i just explain that based on the tertiary carbocartion being a much more stable ion than the primary, the 2-bromo is favoured more as a major product....whats your take guys??
(edited 9 years ago)
Reply 1
Avatar for Pigster
Pigster
20
The second carbon has no hydrogen atoms attached directly to it.
Original post by Pigster
The second carbon has no hydrogen atoms attached directly to it.


ughhhh, lol is that the reason, so when theres a methyl attached, it dosent count as actual hydrogens for electrophilic addition?

Thanks man
Reply 3
Avatar for Pigster
Pigster
20
It is a rather lazy explanation of why. Do you know the inductive effect? If not, bone up.
Original post by Pigster
It is a rather lazy explanation of why. Do you know the inductive effect? If not, bone up.


i dont think its in my spec this year, all i have to do is state it.
Reply 5
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Pigster
20
It is the most shameful thing (IMO) of the OCR A spec that it is not mentioned. So many of my explanations of chemical phenomena require it. Even if it isn't on your spec. (and assuming you're interested in knowing more than the minimum required by your spec.) I'd look it up.
Original post by Pigster
It is the most shameful thing (IMO) of the OCR A spec that it is not mentioned. So many of my explanations of chemical phenomena require it. Even if it isn't on your spec. (and assuming you're interested in knowing more than the minimum required by your spec.) I'd look it up.


Yeah your right tbh, could you give a brief explanation then if you can be bothered? lol just the main points of the inductive effect and jow its applied. Ill look it up fully after
Original post by tariktarkan1907
Yeah your right tbh, could you give a brief explanation then if you can be bothered? lol just the main points of the inductive effect and jow its applied. Ill look it up fully after


Positive carbonium ions (carbocations) have the positive charge reduced by alkyl groups which have a +I (positive inductive) effect.

More stable = more easily formed = more likely intermediate

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