(There is no problem statement etc.) I am having a very hard time figuring out how to assign R/S stereochemistry on certain compounds. I can't rotate molecules in my head without making mistakes, and so I rotate them on paper. Let's take this example: http://avogadro.chem.iastate.edu/CHEM331/331FinalKeyF03.pdf Go to page 6 please, we have to label compounds. When a molecule has 2 atoms in the plane, + 1 in the front and 1 in the back, I can rotate them. I keep one atom fixed, usually #2 (4 being the smaller, 1 the largest), and rotate the other 3. However, and this is where I need help, I don't know what to do when I have molecules such as the ones on the left, where 2 are in the back and 2 in the front, and none in the plane of the paper/screen. How can I rotate those on paper in order to assign R/S stereochemistry? Thank you for any help you can give me! ~J.