bakeit1 Posted October 23, 2008 Share Posted October 23, 2008 Hey all, i'm learning about alkene mechanisms and had a general question regarding AMA. Can something that usually only does MA have an exception and do AMA? If so, how, thanks. Link to comment Share on other sites More sharing options...
big314mp Posted October 23, 2008 Share Posted October 23, 2008 When adding water across a double bond, the hydroboration-oxidation reaction will give you anti markovnikov addition. http://en.wikipedia.org/wiki/Hydroboration-oxidation_reaction Link to comment Share on other sites More sharing options...
bakeit1 Posted October 23, 2008 Author Share Posted October 23, 2008 Ok, however, on a test I just took there was a reaction with an alkene and HBR where the HBR did AMA which ALWAYs is MA. You had to explain why the AMA of HBR was more stable, how's this possible? Link to comment Share on other sites More sharing options...
big314mp Posted October 23, 2008 Share Posted October 23, 2008 What was the alkene? And was there a peroxide present? Link to comment Share on other sites More sharing options...
bakeit1 Posted October 23, 2008 Author Share Posted October 23, 2008 I forgot the alkene, but yah I believe peroxide was present. Link to comment Share on other sites More sharing options...
big314mp Posted October 23, 2008 Share Posted October 23, 2008 With HBr + Alkene, the reaction usually follows markovnikov's rule. This is due because MA favors the more stable carbocation. Now when a peroxide is added, the mechanism changes. The peroxide acts as the initiation step for a radical chain reaction: http://en.wikipedia.org/wiki/Free_radical_addition Link to comment Share on other sites More sharing options...
bakeit1 Posted October 23, 2008 Author Share Posted October 23, 2008 So other than in the presence of peroxide, is this the only time HBR would bond via AMA to an alkene in terms of stability? Thanks btw. Link to comment Share on other sites More sharing options...
big314mp Posted October 24, 2008 Share Posted October 24, 2008 Yeah, its the only one I can think of off the top of my head (read: I haven't looked too hard). Its one of those textbook example things that you just memorize. Link to comment Share on other sites More sharing options...
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