Illustrated Glossary of Organic Chemistry

Isoprene: IUPAC name 2-methyl-1,3-butadiene.  A simple conjugated diene natural product produced by many plant species. The "building block" of terpenes and terpenoids, although terpenes are actually biosynthesized from dimethylallyl pyrophosphate and isopentenyl pyrophosphate. One counts the number of isoprene units to categorize a terpene as a monoterpene, diterpene, etc.

Isoprene

comes from

The carbon skeleton of limonene (a terpene) can be broken into two isoprene units (colored in red and blue).