[briteyellowness]

am i right in saying that 1,2-epoxy-1-methylcyclohexane has 2 stereocenters but only 2 stereoisomers (instead of 4)?  because it can only assume 1R2S or 1S2R because forming 1R2R and 1S2S will break the epoxide ring and thus impossible?

[Winga]

By ChemDraw,

[briteyellowness]

i'm slightly confused on how that works, because in that drawing, there would be three planar bonds at the two carbons that are used to form the expoxide and then one bond that sticks out whereas i thought sp3 bonds should be tetrahedral so there should be one bond that sticks out and one bond that goes in at each carbon.

[alphahydroxy]

I think your confusion arises simply from the conventions of drawing chemical structures. The two epoxide carbons aretetrahedral but are drawn as if they have 3 planr bonds for 'clarity'. obviously in this case the clarity is replaced with confusion to some degree!

The epoxide can indeed be cis or trans as drawn up above, thus the 4 diasteroisomers are all 'available'.