[Stamos666]

     What is driving me crazy is that i have no idea WHICH molecule goes where in a 3D model of a molecule. Is there any rule of thumb as to which substituents go in front of the plane of the paper or the back? I know that depending on how you rotate it, certain molecules are in the front and back but I'm talking about standard basic molecules with no special rotation or anything.

For example, 3-Methylhexane.

In the chiral center, WHICH molecule is gonna be in the front or back of the paper? I've been looking everywhere, even drawing models, but I have no idea which goes where!

[sjb]

There is no absolute prescribed standard. For some cases, it may be easier to draw the group with the lowest priority at the back (which is it here?), just to help drawing the rest of the molecule with the prescribed stereochem. But in reality structures are usually drawn to make reacting centres clear, which may or may not be at odds with this.

S

[Stamos666]

The lowest in priority here is definitely the H. However I have no idea where the other ones go 3D-wise. Which is facing me? It could be anything!

[sjb]

As you have not given any stereochemical descriptors in your name, then that's actually right. If you want to go down the route of a chiral compound, so for instance (R)-3-methylhexane, then it may be useful to point the hydrogen at the back, then think of the other three groups (the methyl, ethyl and propyl) as like 3 prongs of an inverted umbrella (with the hydrogen as the handle).