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.
Your comment is correct where you assign the priority.

Rather than "rotating" or "flipping" the molecule, consider "looking" at it from the angle which makes the H atom be at the back.  In the graphic it is drawn to the left side, so place yourself on the right side and look down the bond.



The priority groups 1-2-3 run anticlockwise, hence it has the S configuration.