[sahar58]

How can I prepare trans diol from alkene? use OsO4 or mcpba?

Does it depends on that alkene is trans or cis?

as I know if I use mcpba, if reactant alkene is trans, it will retain its configuration, but what about  OsO4?

[UG]

As far as I am aware, hydroxylation with OsO₄ occurs with syn addition. Not sure what you mean by the trans diol, there are no double bonds left. Unless of course, it's on a ring, with OsO₄ it'll be a cis diol.

[sahar58]

As far as I am aware, hydroxylation with OsO₄ occurs with syn addition. Not sure what you mean by the trans diol, there are no double bonds left. Unless of course, it's on a ring, with OsO⁴ it'll be a cis diol.

yes i mean cyclic, but what about acyclic, if i want to have anti diol?

how configuration of reactant (I mean if alkene is cis or trans) affect configuration of product? if alkene is trans, then add OsO4, we will have anti or syn diol? (in acyclic) or trans and cis in cyclic?

[UG]

yes i mean cyclic, but what about acyclic, if i want to have anti diol?

how configuration of reactant (I mean if alkene is cis or trans) affect configuration of product? if alkene is trans, then add OsO4, we will have anti or syn diol? (in acyclic) or trans and cis in cyclic?

If it is an aliphatic diol, i.e straight chain then you cannot have geometric isomers.

[sahar58]

yes i mean cyclic, but what about acyclic, if i want to have anti diol?

how configuration of reactant (I mean if alkene is cis or trans) affect configuration of product? if alkene is trans, then add OsO4, we will have anti or syn diol? (in acyclic) or trans and cis in cyclic?

If it is an aliphatic diol, i.e straight chain then you cannot have geometric isomers.

what about both OH, out of plane or back of plane?

[Dan]

If it is an aliphatic diol, i.e straight chain then you cannot have geometric isomers.

I think the point here is that you can get erythro/threo isomers.

For example, if you take Z-but-2-ene and treat it with OsO₄ you will not get the same isomer as when you treat E-but-2-ene with OsO₄.

Similarly, treatment of Z-but-2-ene with OsO₄ will give different compounds than treatment with mCPBA.

sahar58 - look up these mechanisms of dihydroxylation and attempt the question. Showing an attempt is required - see forum rules.