Can you illustrate Markownikow's rule in the context of hydrohalogenation of olefins?

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Answer 1 · 2017-05-16T16:21:43

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$Markownikow addition$ $"Markownikow addition"$ describes the general preference of unsymmetrical olefins towards addition of hydrogen halides.

i.e. $R C H = C H_{2} + H X \to R C H_{2} C H_{2} X$ $RCH=CH_2 + HXrarrRCH_2CH_2X$

$To him that hath hydrogen shall be given hydrogen.....$ $"To him that hath hydrogen shall be given hydrogen....."$

This reflects the stability of the secondary carbocation as compared to the primary carbocation:

$X H + R C H = C H_{2} \to R + C H - C H_{3} + X^{-}$ $XH+ RCH=CH_2 rarr Rstackrel(+)CH-CH_3 +X^-$

VERSUS

$X H + R C H = C H_{2} \to R C H_{2} - + C H_{2} + X^{-}$ $XH+ RCH=CH_2 rarr RCH_2-stackrel(+)CH_2 +X^-$