Steam Distillation of Monoterpenes (
)-(+)-Carvone and (
from Caraway Seeds/Analysis of Products by Infrared Spectroscopy and TLC
March 9, 2007
Methods and Background
The purpose of the experiment was to isolate the essential oil, which contained (
as its major component and (
)-(+)-Limonene as a minor component, from caraway seeds by
steam distillation and analyze and verify the mixture of products by infrared spectroscopy and
Carvone is a type of terpene, a class of hydrocarbon compounds that is typically produced in
Terpenes are created from units of isoprenes, which contain 5 carbons; Carvone is a
monoterpene, meaning it is made of two isoprenes and thus contains 10 carbons.
biosynthesis of Carvone, mevalonate rearranges a double bond to from isoprene, which then
reacts with another molecule of mevalonate by electrophilic attack to produce an intermediate
that performs an intramolecular electrophilic attack to yield (
)-(-)-Carvone and (
(upon addition of oxygen).
Carvone exists in two enantiomers, (
)-(-)-Carvone, found in spearmint leaves, and (
Carvone, found in caraway seeds.
Enantiomers are types of stereoisomers, which are isomers
having the same molecular skeleton, but different spatial arrangements of their atoms.
Enantiomers are related as nonsuperimposable mirror images and are thus termed chiral.
Specifically, in order for an atom in a molecule to be a chiral center (stereocenter), it must be
bonded to four different substituent groups.
) and (
) configuration are assigned to molecules
following the Cahn-Ingold-Prelog (CIP) rules, which first order the four substituents based off
molecular mass (where the substituent with the most mass equals 1 and the substituent with the
least mass equals 4) and then determine configuration on the basis of clockwise (
) rotation, moving from 1 to 4.
The two enantiomers of Carvone spatially
differ in that the (
) enantiomer has a hydrogen coming “out” and a 1-methylethenyl group
going “in” at the stereocenter, while the (
) enantiomer has the hydrogen going “in” and the 1-
methylethenyl group coming “out.”
Enantiomers also demonstrate identical physical properties,
so the two enantiomers of Carvone would give the same infrared (IR) spectra, retention factor
) values, boiling points, and nuclear magnetic resonance (NMR) spectra.
However, the two
enantiomers would have different optical rotations, as they rotate plane-polarized light the same
amount of degrees, but in opposite directions (designated by + or -).
If the two enantiomers were
in a 1:1 mixture (racemic mixture), though, there would be no net rotation of plane-polarized