#oxirane

[myorgonotes]

Can form oxiranes from MCPBA or Dimethyl Dioxirane (As my professor fondly calls it, "Spectacles")

[myorgonotes]

Attack on Oxiranes are usually for steric (size reasons) thus are Regioselective.

We can change that by adding H+ and protonating it. Now, the more crowded Carbon will be attacked because it is positive. Apparently it only works for a weak base?

In other words: Acid Catalyzed reaction open oxirans and changes the regioselectivity