Code Unsubstituted Structure
n (n = 5-12) ring of size n
ACENAP acenaphthene
ADAMAN adamantane
ANTHRA anthracene
BILINE biline
CAROTE carotene
CEPHAL cephalosporins
FLUORN fluorene
IBOGAM ibogamines
INDENE indene
MORPHN morphine
NAPHTH naphthalene
NORBRN norbornane
PENICL penicillins
PHENAN phenanthrene
PHORBN phorbine
PORPHN porphines
PORPHY porphyrazine
PROSTA prostaglandins
PURINE purine
SEQTER sesquiterpenes
STEROD steroids