Attacking epoxides

[SaintJude]

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Say you have a compound that includes a cis-epoxide Then the compound is treated with a H+ and H20 to open the epoxide ring.

2 diols will form (because the water can attack at either carbons of the epoxide)

Will the diols have cis or trans configuration? And how do you know?

 

[Pisiform]

I think anti-addition so trans ... not sure if I remember correctly

 

[MedPR]

Yup, pretty sure it's anti addition. The H+ opens the ring, forming a carbocation and a C-H2O, then the C-H2O is deprotonated and the carbocation gets a hydroxide added to it from the solvent.

 

[SaintJude]

The question is from Princeton Hyperlearning MCAT Science Workbook btw (2nd passage). I looked in to this further and apparently opening of epoxides in acidic and basic condition leads to an SN2-like inversion of stereochemistry.

 

[Ssina]

I think it depends what the reaction conditions are... if basic it'll be Sn2 like so it will add anti, but if acidic and it goes through the carbocation, then it should be able to add from either side, since carbocations are planar

 

[Ssina]

The question is from Princeton Hyperlearning MCAT Science Workbook btw (2nd passage). I looked in to this further and apparently opening of epoxides in acidic and basic condition leads to an SN2-like inversion of stereochemistry.

ok that's what I thought originally, so either way it'll be Sn2 like which will be anti addition of Nu

 

[MedPR]

This might help. It uses an alcohol instead of water, but it's the same concept.

http://clem.mscd.edu/~wiederm/oc2chp/oc2chpethers/page8.htm