Isoprene

Names

Preferred IUPAC name

2-Methylbuta-1,3-diene

Other names

2-Methyl-1,3-butadiene
Isoprene

Identifiers

CAS Number

78-79-5^Yd

3D model (Jmol)

CHEBI:35194^Y

6309^Y

C16521^Y

0A62964IBU^Y

InChI=1S/C5H8/c1-4-5(2)3/h4H,1-2H2,3H3^Y

Key: RRHGJUQNOFWUDK-UHFFFAOYSA-N^Y
InChI=1/C5H8/c1-4-5(2)3/h4H,1-2H2,3H3

Key: RRHGJUQNOFWUDK-UHFFFAOYAS

SMILES

CC(=C)C=C

Properties

C₅H₈

68.12 g/mol

0.681 g/cm³

−143.95 °C (−227.11 °F; 129.20 K)

Boiling point

34.067 °C (93.321 °F; 307.217 K)

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

(what is ^YN ?)

Infobox references

Isoprene, or 2-methyl-1,3-butadiene, is a common organic compound with the formula CH₂=C(CH₃)-CH=CH₂. In its pure form, it is a colorless volatile liquid. Isoprene is produced by many plants, and its polymers are the main component of natural rubber. C.G. Williams named the compound in 1860 after obtaining it from thermal decomposition (pyrolysis) of natural rubber; he correctly deduced the empirical formula C₅H₈.

Isoprene is produced and emitted by many species of trees (major producers are oaks, poplars, eucalyptus, and some legumes). Yearly production of isoprene emissions by vegetation is around 600 million metric tons, half from tropical broadleaf trees and the remainder primarily from shrubs. This is about equivalent to methane emissions and accounts for ~1/3 of all hydrocarbons released into the atmosphere.

Isoprene is made through the methyl-erythritol 4-phosphate pathway (MEP pathway, also called the non-mevalonate pathway) in the chloroplasts of plants. One of the two end products of MEP pathway, dimethylallyl pyrophosphate (DMAPP), is catalyzed by the enzyme isoprene synthase to form isoprene. Therefore, inhibitors that block the MEP pathway, such as fosmidomycin, also block isoprene formation. Isoprene emission increases dramatically with temperature and maximizes at around 40 °C. This has led to the hypothesis that isoprene may protect plants against heat stress (thermotolerance hypothesis, see below). Emission of isoprene is also observed in some bacteria and this is thought to come from non-enzymatic degradations from DMAPP.

Isoprene emission in plants is controlled both by the availability of substrate (DMAPP) and by enzyme (isoprene synthase) activity. In particular, light, CO₂ and O₂ dependencies of isoprene emission are controlled by substrate availability, whereas temperature dependency of isoprene emission is regulated both by substrate level and enzyme activity.

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