HO NH> NH>
HO
HO \
Dopamine N
H
SerotoninHere we are simply not drawing the Cs and most of the Hs. We are
drawing only the bonds connecting the various atoms together.
So now, at last, we can articulate the rules for drawing and inter-
preting molecular structure diagrams. Covalent bonds are drawn as
lines. If there is no letter explicitly shown at the end of a line, then
it is assumed there is a carbon atom in that location. Thus, each line
(bond) has a carbon atom at either end, unless another atom is explic-
itly drawn. Atoms other than carbon are indicated: N for nitrogen, O
for oxygen, P for phosphorus, F for fluorine, and so forth. What about
the hydrogen atoms? Because we know that carbon forms four bonds,
any bonds not shown explicitly are assumed to be with hydrogen,
enough hydrogens so that the total number of bonds per carbon
equals four. Hydrogen atoms forming bonds with other elements
(such as nitrogen and oxygen) are explicitly drawn in.
That’s it for the basic rules. Really pretty simple!
One of the things we can easily do with this shorthand notation
for molecular structure is compare similarities in shape between
molecules. For example, one can see that these molecules—dopamine
and norepinephrine, which are neurotransmitters; amphetamine,
methamphetamine, and ephedrine, which are psychoactive drugs;
and phenylalanine, an amino acid—all share a basic similarity of
shape, something about their gestalt, or form.