SMILES syntax
atom : [ <mass> symbol <chiral> <hcount> <sign<charge>> <:class> ]
bond : <empty> | - | = | # | : | .
Common elements, in the organic subset B,C,N,O,P,S,F,Cl,Br,I, in their lowest common valence state(s), can be written without brackets. If bonds are omitted, they default to single or aromatic, as appropriate, for juxtaposed atoms.