[Niquola012]

For something like 4-bromo-2-pentene or any asymmetric carbon center, how do you know where to place the substituents as far as what is in the plane of the carbon, what is coming toward the viewer, and what is going away on the fourth carbon? In general, is it arbitrary or is there a methodology to it? My professor says it doesn't matter and no one has been able to answer my question. I feel like I'm drawing molecules that don't exist sometimes.

[TwistedConf]

For something like 4-bromo-2-pentene or any asymmetric carbon center, how do you know where to place the substituents as far as what is in the plane of the carbon, what is coming toward the viewer, and what is going away on the fourth carbon?

Drawing the asymmetric carbon in 3D requires first knowing what the configuration (R or S) is. If you don't have a specific configuration in mind, you would at least know that there are two different options (again, R or S) and you should be able to draw either of those correctly.

That being said, there are several different ways of drawing (on paper) an asymmetric carbon with a given configuration that are all equivalent and all correct at the same time... so your questions doesn't have a clear black and white answer. You place the substituents as you like them, as long as following the rules for assigning configuration based on your drawing yields the intended configuration.

[antimatter101]

Also, for double bond substituents, there are cis-trans and E-Z designations. Go search them up.

For coordination complexes, there is even more vocabulary needed to describe their stereochemistry, such as meridonial and facial. (Fac-mer)

Just search them up!