isoprene

Examples of isoprene in the following topics:

• Terpenes

  • Terpenes may be considered to be made up of isoprene ( more accurately isopentane ) units, an empirical feature known as the isoprene rule.
  • In the case of the triterpene lanosterol we see an interesting deviation from the isoprene rule.
  • Similar alkyl group rearrangements account for other terpenes that do not strictly follow the isoprene rule.
  • Bromine, hydrogen chloride and hydrogen all add with a stoichiometry of one molar equivalent per isoprene unit.
  • Pyrolysis of rubber produces the diene isoprene along with other products.

• Lipid Biosynthesis

  • Biological lipids originate entirely or in part from two distinct types of biochemical subunits or "building-blocks": ketoacyl and isoprene groups.
  • Using this approach, lipids may be divided into eight categories: fatty acids, glycerolipids, glycerophospholipids, sphingolipids, saccharolipids, and polyketides (derived from condensation of ketoacyl subunits); and sterol lipids and prenol lipids (derived from condensation of isoprene subunits ).
  • Terpenes and isoprenoids, including the carotenoids, are made by the assembly and modification of isoprene units donated from the reactive precursors isopentenyl pyrophosphate and dimethylallyl pyrophosphate.
  • One important reaction that uses these activated isoprene donors is steroid biosynthesis.
  • Here, the isoprene units are joined together to make squalene and then folded up and formed into a set of rings to make lanosterol.

• UV-Visible Absorption Spectra

  • The resulting spectrum is presented as a graph of absorbance (A) versus wavelength, as in the isoprene spectrum shown below.
  • Since isoprene is colorless, it does not absorb in the visible part of the spectrum and this region is not displayed on the graph.
  • If the isoprene spectrum below was obtained from a dilute hexane solution (c = 4 * 10-5 moles per liter) in a 1 cm sample cuvette, a simple calculation using the above formula indicates a molar absorptivity of 20,000 at the maximum absorption wavelength.
  • Fortunately, conjugation generally moves the absorption maxima to longer wavelengths, as in the case of isoprene, so conjugation becomes the major structural feature identified by this technique.

• Polymers

  • He formulated a polymeric structure for rubber, based on a repeating isoprene unit (referred to as a monomer).

• Ziegler-Natta Catalytic Polymerization

  • Their findings permitted, for the first time, the synthesis of unbranched, high molecular weight polyethylene (HDPE), laboratory synthesis of natural rubber from isoprene, and configurational control of polymers from terminal alkenes like propene (e.g. pure isotactic and syndiotactic polymers).

• The Importance of Conjugation

  • A comparison of the absorption spectrum of 1-pentene, λmax = 178 nm, with that of isoprene (above) clearly demonstrates the importance of chromophore conjugation.
  • The spectrum of the bicyclic diene (above right) shows some vibrational fine structure, but in general is similar in appearance to that of isoprene, shown above.

• Vitamins and Amino Acids

  • For example, menaquinone-4 (abbreviated MK-4), has four isoprene residues in its side chain.

• Carotenoids and Phycobilins

  • All carotenoids are tetraterpenoids, meaning that they are produced from 8 isoprene molecules and contain 40 carbon atoms.

• Sulfur Compounds

  • In the most common type of industrial "curing" or hardening and strengthening of natural rubber, elemental sulfur is heated with the rubber until chemical reactions form disulfide bridges between isoprene units of the polymer.

• Basic Structures of Prokaryotic Cells

  • In archaeal cell membranes, isoprene (phytanyl) chains linked to glycerol replace the fatty acids linked to glycerol in bacterial membranes.