Through the looking-glass challenge
Chemistry” (ABC) homepage at http://www.springer.com/
abc and in the journal (volume 410/issue 10)
Through the looking-glass challenge
Reinhard Meusinger 0
0 Institute of Organic Chemistry and Biochemistry, Darmstadt University of Technology , Alarich-Weiss-Str. 4, 64287 Darmstadt , Germany
1 Reinhard Meusinger
We would like to invite you to participate in the Analytical Challenge, a series of puzzles to entertain and challenge our readers. This special feature of “Analytical and Bioanalytical Chemistry” (ABC) has established itself as a truly unique quiz series, with a new scientific puzzle published every other month. Readers can access the complete collection of published problems with their solutions on the ABC homepage at http://www.springer.com/abc.Test your knowledge and tease your wits in diverse areas of analytical and bioanalytical chemistry by viewing this collection. In the present challenge, spectroscopy is the topic. And please note that there is a prize to be won (a Springer book of your choice up to a value of €100). Please read on… scientific explanation. In 1849 Louis Pasteur noticed that the crystals of tartaric acid come in two asymmetric forms that are mirror images of one another. He deduced that the molecule in question is asymmetric and could exist in two different forms that resemble one another as would left- and right-hand gloves. The theoretical explanation for this phenomenon was given by van 't Hoff [1] and Le Bel [2] 3 years later in 1874.
-
Meet the challenge
“How would you like to live in Looking-Glass House, Kitty?”
Alice asked her cat in the novel Through the Looking-Glass,
and What Alice Found There (1871). Only 6 years after Alice
had experienced her adventures in Wonderland, the author
Lewis Carroll (Charles Lutwidge Dodgson) lets Alice enter
another fantastical world, this time by her climbing through
a mirror into another world. “I wonder if they’d give you milk
in there? Perhaps Looking-Glass milk isn’t good to drink…”
Alice says questioningly to her cat. Specular optical activity
had been known for a while then, yet it was still lacking
The compound we are looking for in this challenge exists in
two mirror-image forms as well. One of these forms rotates the
plane of polarization of linearly polarized light clockwise (we
will call it the (+)-compound) and the other rotates it
counterclockwise (the (−)-compound). An interesting feature of these
two forms is that they differ significantly in their smell and
taste. Hence, it should not come as a surprise that both
compounds are found separately in different plants, although they
also exist as a racemic mixture. The name of this substance
derives from one of the oldest known medicinal plants, which
contains a particularly high proportion of it in its seeds. Seeds
of this plant have been found at excavations of 3000-year-old
pile dwellings. Today, this plant is widely cultivated
throughout practically all of Europe. However, the global leader in the
seed oil export of this plant is a Scandinavian country with
long hours of sunlight during the summer, which leads to
fruits with higher levels of essential oil. The fruits and the
essential oil are used in many ways in cooking and in the
preparation of certain medicines and liqueurs. The fruits are
used in breads, cheeses, and even desserts, whereas the fruit
oil is used as a fragrance in soaps, lotions, and breath
fresheners, and has a long tradition of use in folk medicine. The
etymology of the name of this miracle-working plant is
complex and poorly understood, because it has been called by
Fig. 1 The 500-MHz 1H-NMR
spectra of both optical isomers,
measured in dimethyl-d6
sulfoxide. The spectrum of the
(+)-compound is colored blue and
the mirrored spectrum of the
(−)compound is colored red
many names in different regions, with names deriving from
Arabic, Greek, which was adapted into Latin, and Sanskrit.
The English use of the name dates back to the middle of the
fifteenth century and is considered to be of Arabic origin,
probably.
To the best of our knowledge, the compound we are
looking for was first isolated in 1840 from its essential oil,
and Berzelius named it by suffixing “ol” to the plant’s Latin
name. The difference between two compounds, both isolated
from essential oils, was described in 1876 as “Y is already
Fig. 2 The spectra from Fig. 1 in
greater detail
distinguished physically from X by the fact that it penetrates
much less into cork, and does not show the property of
gnashing when rubbing on a glass bottleneck, like X and other
thin-liquid essential oils” [
3
]. Despite the difficulty in
determining the structure, the empirical formula was determined
correctly as C10H14O.
Today, structural analysis is facilitated greatly by use of
spectroscopic methods. First, we look at the 1H-NMR
spectrum of the substance, measured in dimethyl-d6
sulfoxide. In Figs. 1 and 2, the 1H-NMR spectra of both
optical forms are shown in an unusual mirrored manner,
in which (...truncated)