Terpenes: The Isoprene Rule 4

Isoprene Links Heads or Tails? Head to tail couplings are most common.

Common Carbon Backbone

Some Common Terpenes

Terpenes Classification of Terpenes Class Number of carbon atoms Monoterpene 10 Sesquiterpene 15 Diterpene 20 Sesterpene 25 Triterpene 30 Tetraterpene 40

a-Phellandrene (eucalyptus) Terpenes Representative Monoterpenes OH O H a-Phellandrene (eucalyptus) Menthol (peppermint) Citral (lemon grass)

Representative Sesquiterpenes H a-Selinene (celery)

Representative Diterpenes OH Vitamin A

Squalene (shark liver oil) Terpenes Representative Triterpene tail-to-tail linkage of isoprene units Squalene (shark liver oil)

Terpenes isoprenyl (C5) --> geranyl (C10) geranyl (C10) --> farnesyl (C15) farnesyl (C15) --> squalene (C30) Generic: C10 monoterpenes, C15sesquiterpenes, C20 diterpenes, C30 triterpenes, C40 tetraterpenes

Rings form by intramolecular carbon-carbon bond formation. Cyclization Rings form by intramolecular carbon-carbon bond formation. + OPP OPP E double bond Z double bond

Limonene H – + + OH H2O a-Terpineol