ly 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
, and dill
holds a special place in the hearts and syllabi of first
semester organic chemistry
walks in, carrying his normal small basket
of props for the class. He says nothing, instead drawing
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
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
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 molecule
s that the
class will soon come to hate.
The basic structure (see below) of Carvone has
an extremely interesting property. The same
, with the same arrangement
s, can form in two distinct ways,
allowing for a type of stereoisomer
. 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
exist on Earth. A typical in vitro
produces a mix of both isomer
called a racemate
(Pasteur's "racemic acid
actually consisted of a mix of the isomers of
). An in vivo
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 defect
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.
/ \ / \
/ \ / \
H2C C====O H2C C====O
\ / \ /
\ / \ /
/ . . \
/ . . \
H3C----C\ H H3C----C\ H
caraway, dill spearmint
............ 230°C @ 101.3kPa
............... 88°C (R), 95°C (S)
....... 0.0533kPa @ 20°C
......... 0.956 - 0.960 @ 25°C
...... 1.495 - 1.499 @ 20°C
........ 61° (R-, S+)
in ................. ethanol
, propylene glycol
Insoluble in ............... glycerin
(oral, rat) ......... 1640 mg/kg
The Merck Index, 12th ed.
McMurray's Organic Chemistry, 4th ed.