Table 5 Atom and bond primitives for encoding of atom types and atom environments in SMARTS
Feature | SMARTS encoding | Special case |
|---|---|---|
Atom primitives | ||
 Element | Atomic symbol | Lower case indicating aromaticity |
 Formal charge | ±<integer> | Uncharged represented as +0 |
 Implicit hydrogen count | h<integer> |  |
 Explicit degree | D<integer> |  |
 Valence | v<integer> |  |
Bond primitives | ||
 Single bond | – |  |
 Double bond | = |  |
 Triple bond | # |  |