# R or S configuration of propane-1,2-diol

What is the specific configuration (R or S) of this compound?

My answer is R, because $$\ce{H}$$ is not in the back so I flipped the compound. Is my answer right?

My teacher is telling me it is S, though I'm pretty sure that it is R. That made me very confused.

What I did is that I got S at the beginning, but because $$\ce{H}$$ is not in the back, I flipped the compound and got the answer R. My teacher flipped the compound in a way that the answer was still S.

$$\ce{OH}$$ (1), $$\ce{CH2OH}$$ (2), $$\ce{CH3}$$ (3), $$\ce{H}$$ (4) from 1 to 3, anticlockwise which means it is S configuration. But $$\ce{H}$$ is not in the back, Therefore rotate the compound and the answer should be the opposite to S which means it is R.

• Well clearly one of you is wrong. Perhaps you could add some diagrams to your question to show what you mean. I have some difficulty in visualising what you are trying to say. – bon Feb 17 '16 at 18:56
• @saf, here's a hint. The H isn't in the front either... – jerepierre Feb 17 '16 at 18:59
• Words of caution about flipping structures: chemistry.stackexchange.com/questions/99721/… – user55119 May 11 '19 at 1:53