Hi, I was doing research on serotonin and I realized that most of the drawings show NH written downward, as if the N is on top of the H, but when it's not written that way, is it meant to be HN or NH? I cannot for the life of me find this answer online anywhere, and my chemistry knowledge is very basic. So just to clarify I'm looking at NH2 NH OH vs. NH2 HN OH. If you could get back to me ASAP that would be great.
There is no correct orientation for the way chemists draw bonds on molecules--I think that is causing your confusion! The important thing in identifying a molecule is what atom is attached to which. For example, I would still identify you as yourself even if you were doing a hand stand.
We have to remember that molecules are three dimensional, real objects, just as we are, and they tumble and move around as we do. The straight lines connecting the atoms--called covalent bonds--are unlikely to break, and if they do, it changes the identity and the name of the molecule.
So, when it comes to drawing molecules, we have to get used to seeing them in all sorts of orientations. As long as the connections stay the same--for example, I would not attach your foot to your arm, that would be wrong--we can identify them.
You are probably looking at something called condensed chemical notation which is a convenient shorthand that we use to draw molecules.
This is a shorthand which omits showing most of the lines (bonds) linking the atoms (letters) because it is understood that H ALWAYS has only one bond, not two. Also, N usually has three bonds, but sometimes can have four or two. If an atom has a number of bonds other than what is expected (this is something predicted based on something called valence) it WILL have a charge. So, if N has four bonds, it will have a + sign written next to it. If it has two bonds, it would have a minus sign written next to it. Carbon almost always has four bonds. Oxygen usually has two, but can have one (and then it will be negatively charged) or could have three (and then it would be positively charged.)
If you want to know why these rules are the way they are, you have to learn more about covalent bonding and Lewis structures, which I don't have space to go into here...but trust that these are well-known rules of nature.
So you can see CH3NH2 and predict where all the bonds are. Since H can only have one bond, it has to be the "fringe" as I call it, on the outside. The inner atoms are C and N, bonded to each other, and C has three hydrogens (giving it 4 bonds) and N has two hydrogens (giving it three bonds.)
Now for serotonin!
Because the rule is that H can only have one bond in a molecule, not two (this is because it has only one electron to share in a covalent bond), the H has to be attached to the N if you see NH, regardless of whether the H is "up" or "down" or sideways or diagonal. Molecules don't know that we write from left to right on paper!
So, having the H next to N is the only important piece of information that tells a chemist that the H is bonded to N and not to some other atom. It does not matter what orientation the H is next to the N. As I tell my students, YOU get to choose how you draw it! Just like I could draw a picture of you, upside down, lying down, or standing up, as long as all your limbs were attached correctly we would know it was you.
I hope that helps!