This is a question that has bothered me for some time. I have always thought that the part of one molecule will only attack part of another molecule if it has a higher positive charge. So with this in mind, why does the alkene double bond attack the $\ce{O}$ atom of $\ce{OsO4}$. Isn’t the $\ce{O}$ atom negatively charged?

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    $\begingroup$ I am not sure whether it is the alkene that initiates bond formation. However, take a look at the mechanism. It is a cycloaddition. For all we know, the oxygen from the osmium tetroxide may be the one initiating the formation of the bond. I will try to look some journals and post what I find. $\endgroup$ Dec 8, 2016 at 4:29
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    $\begingroup$ Not all reactions are driven by simple attraction of oppositely charged atoms. Consider alkene hydrogenation, acetylene trimerization, or the Diels–Alder thing. $\endgroup$ Dec 8, 2016 at 5:59

2 Answers 2


I have a suggestion that could explain the attacK of electron pair of alkene pi bond to the oxygen of osmium tetroxide : The electron pair of alkene pi bond repels the electron density of the oxygen when the osmium tetroxide approaches the alkene, creating a temporary δ+ on the oxygen that is closer to the pi bond of alkene. The electron-rich alkene then attacks the electron-poor oxygen.

Dimitrios Kariotoglou

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    $\begingroup$ Are these your opinions? Please put in references to literature, or else the answer is just speculation. And this explanation seems quite far-fetched to me. I could be wrong, but the right way to refute my disapproval will be to find literature and add it in. Good-day. $\endgroup$ Apr 16, 2020 at 9:25

Yes. But check the formal charge on the Osmium. It is so very positive that it actually steals electron density from the Oxygen.


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