orgo question

[biostudent101]

hi,

1-butene with Br2 in methanol gave 1-bromo-2-methoxybutane? can someone explain to me why Br went to the 1st carbon and the OCH3 went to the 2nd carbon.
thanks!

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[DrSpeed]

When the Br attacks you get a bromonium ion. The ethoxide ion then attacks anti-markovnikov. pretty much the same mechanism as hydroboration-oxidation.

 

[NumbaOneStunna]

When the Br attacks you get a bromonium ion. The ethoxide ion then attacks anti-markovnikov. pretty much the same mechanism as hydroboration-oxidation.

Everything the above poster said plus the logic behind attacking the more substituted carbon of the carbon-bromonium-carbon triangle is that the electron density of the triangle is shifted more on the C-Br bond of the less substituted carbon than the C-Br bond of the more substituted carbon. This makes sense because then the more substituted carbon will get the weaker bond and a delta positive which it can handle np np b/c of hyperconjugation. Since the more substituted carbon is delta positive, this is where the water attacks making the 1 bromo 2 methoxy.