Carvone, 2-methyl-5-(1-methylethenyl)-2-cyclohexene-1-one, a naturally occuring monocyclic monoterpene ketone, exists as a strongly scented oil in several species of edible plants.

Though most know it as a primary component in the flavor and odor of spearmint, caraway, and dill, carvone holds a special place in the hearts and syllabi of first semester organic chemistry students everywhere.

----------


The professor walks in, carrying his normal small basket of props for the class. He says nothing, instead drawing a structure on the overhead. "Aww, man!", most of the class thinks, expecting that this means a pop quiz. But then, instead of instructing the class to name functional groups or, *gasp*, the full IUPAC name, the professor passes around a small vial containing a clear, pale-yellow thin fluid. "Smell it", he instructs.

Most of the class readily recognizes it as something minty, a few even get it correct, as spearmint.

"You've all just sniffed carvone, the main constituent of spearmint oil, which I've drawn on the overhead.". He then shuffles through his basket-o'-goodies, and passes around another vial, which looks similar to the first.

Fewer people recognize this smell, a sort of oily odor with a hint of mint-like spiciness, though a few say it smells vaguely like dill.

"Dill works, though you'll find it in a much higher concentration in caraway seeds", the professor points out. "You've all just sniffed carvone, which I've drawn on the overhead.".

The class looks confused, and even the strange guy in the back (who everyone suspects has just a tad too much "experiential knowlege" of organic chemistry) looks up and cocks his head to the side like a confused puppy.

"In 1849, Louis Pasteur cooled a solution of racemic acid in a dish on his window sill, allowing it to crystalize...", the professor begins, in his explanation of a property of molecules that the class will soon come to hate.

----------


The basic structure (see below) of Carvone has an extremely interesting property. The same chemical structure, with the same arrangement of bonds, can form in two distinct ways, allowing for a type of stereoisomer called an enantiomer. These relate to one another in the same way a left and right hand do - They have all the same parts, and look mostly alike, but no matter how hard someone tries (short of turning it inside-out), a left-handed glove will not fit a right hand.

This property has numerous consequences, particularly for carbon-based life forms as exist on Earth. A typical in vitro synthesis produces a mix of both isomers, called a racemate (Pasteur's "racemic acid" actually consisted of a mix of the isomers of tartaric acid). An in vivo synthesis, such as a human cell might use to produce a given substance, will almost always produce a single isomer rather than a racemate. As a result, ingestion of the R form may have different effects than ingestion of the S form. The most well known example of this occurred with the drug thalidomide, used in the 1960's for morning sickness. The S enantiomer of thalidomide would correctly alleviate nausea, while the R version caused severe birth defects in the growing fetus.

Carvone has no particular medicinal activity in humans. However, the sharply different taste and smell of the two enantiomers make it almost ubiquitously used as an example in any organic chemistry class.

----------


                  CH3                       CH3
                 /                         /
                /                         /
         HC====C                   HC====C
         /      \                  /      \
        /        \                /        \
     H2C          C====O       H2C          C====O
        \        /                \        /
         \      /                  \      /
          C----CH2                  C----CH2
         / .                       . \
        /   .                     .   \
H3C----C\    H            H3C----C\    H
        \\                        \\
         \\                        \\
          CH2                       CH2

      S-(+)-carvone             R-(-)-carvone
      caraway, dill               spearmint
          oily                      minty

----------


Properties:
Boiling point ............ 230°C @ 101.3kPa
Flash point ............... 88°C (R), 95°C (S)
Vapor pressure ....... 0.0533kPa @ 20°C
Specific gravity ......... 0.956 - 0.960 @ 25°C
Refractive index ...... 1.495 - 1.499 @ 20°C
Optical rotation ........ 61° (R-, S+)
Soluble in ................. ethanol, methanol, propylene glycol
Insoluble in ............... glycerin, water
LD50 (oral, rat) ......... 1640 mg/kg

Sources:
The Merck Index, 12th ed.
McMurray's Organic Chemistry, 4th ed.
http://hexane.chem.uiuc.edu/cyberprof/public/chemistry/102x/Lecture/lect21c.html
http://www.ims-global.com/insight/news_story/0301/news_story_030116.htm
http://www.ensia.inra.fr/~courtois/fidel/Lisbon/flaves/sec2/sec222.html
http://www.thegoodscentscompany.com/data/rw1002741.html
http://www.uiowa.edu/~chemsafe/MSDS/(R)-(-)-Carvone.html
http://www.uh.edu/engines/epi604.htm

Log in or registerto write something here or to contact authors.