Volatiles for the Perfume Industry
M Séquin, San Francisco State University, San Francisco, CA, USA
Ó 2017 Elsevier Ltd. All rights reserved.
This article is a revision of the previous edition article by D.J. Murphy, volume 3, pp. 1180–1181, Ó 2003, Elsevier Ltd.
Glossary
Absolute In perfume industry: Product obtained through
extraction of the concrete with ethanol.
Chiral Asymmetric or ‘handed.’
Concrete In perfume industry: The product of extractions
of volatiles.
Enantiomers Compounds that are mirror images of each
other.
Essential oil Volatile, fat-soluble plant oil. In perfume
industry: The product of steam distillation of plant
materials.
Hydrodiffusion A type of steam distillation.
Inflorescence A group or cluster of flowers on a branch or
a system of branches.
Introduction
Plants and their volatile compounds have been the major sources of fragrances for perfumes and cosmetics since ancient
times. This article describes the composition of typical plant
scents, the major chemical families of volatile compounds
that are found in them, their perceived functions within plants,
and their interactions with other living things, addressing also
the human perception. Highly sensitive analytical methods
have been developed to analyze the complex mixtures that
compose the scents, methods that also have vast applications
in the analysis of perfumes. Plants not only are major contributors as perfume ingredients, but their volatiles have been the
inspiration for synthetic components, be they nature-alike or
new structures, that further enlarge the palette of volatiles
useful for the composition of perfumes. Historical notes on
the trading and use of fragrant volatiles through the ages
conclude the article.
Volatiles in Plants: Structures and Biological
Functions
Plants synthesize a wealth of volatile compounds, that is,
compounds that have (relatively) high vapor pressures and
vaporize easily into the air. As plants are usually rooted in
one place, the volatiles are a means of long-distance communication with other organisms. While some plant volatiles attract
pollinators in the form of floral scents, others deter animals that
otherwise would feed on plant parts. Yet other volatiles can act
as long-distance warning signals toward insects. Furthermore,
many plant volatiles have antimicrobial activity and thus can
act as protection for vital plant parts like flowers. The components of plant scents tend to be of an oily nature at ambient
temperatures, a characteristic that gave them the name ‘essential
Encyclopedia of Applied Plant Sciences, 2nd edition, Volume 2
Isoprenoids Same as terpenes. Secondary metabolites
composed of isoprene units.
Mediterranean climate Climate type characterized by hot,
dry summers and cool, wet winters.
Monoterpene Terpenes consisting of two isoprene units,
thus having 10 carbon atoms.
Sesquiterpene Terpenes consisting of three isoprene units,
thus having 15 carbon atoms.
Supercritical CO2 Carbon dioxide subjected to pressure
becomes supercritical and has liquid properties while
remaining in a gaseous state.
Terpenes See Isoprenoids.
oils,’ ‘essential’ here being the characteristic or essence of a scent.
Evaporation from leaf blades of the volatile liquids can provide
a cooling effect for plants on hot days. Furthermore, oily layers
on leaves oozing out on a warm day can protect plants from
desiccation; these are desirable and common traits in plants
of climates with long sequences of drought as in Mediterranean
climates. Plant volatiles are secondary metabolites, formed from
primary metabolites like sugars, fatty acids, and amino acids,
following defined biosynthetic pathways.
Plant smells are complex mixtures of sometimes several
hundred different volatile compounds that evaporate into the
air at elevated temperatures. When walking through a pine
forest or a rose garden on a warm day we readily notice the
scents. Volatiles can be produced in flowers, fruits, and leaves.
The composition of plant scents and the concentration of
compounds in them are determined by the type of plant, its
age, its growth phase, and the ambient climatic conditions.
Examples of volatiles found in plant scents are shown in
Figures 1–3. Many compounds are common in various plant
smells, but in different concentrations. For example, the widespread a-pinene is a major component of pine oil as its name
suggests, but also contributes 40–50% to the essential oils of
rosemary herb, and traces of a-pinene can be found in rose
oil and in lavender. Other common volatiles include limonene,
with the scent of citrus, and geraniol with the smell of roses. In
contrast, some volatiles are specific to a few distinct plants, like
the compound jasmone (shown in Figure 5) that provides its
characteristic scent to jasmine flowers.
Molecules that compose plant volatiles have general chemical characteristics in spite of their structural diversity. They are
organic molecules of relatively small sizes (on a molecular
scale), with up to about 15 carbon atoms. They are composed
mostly of hydrocarbon structures; therefore they are nonpolar
and insoluble or only slightly soluble in water. There is little
intermolecular bonding between the molecules as there are
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10 C, sending out volatiles with a rotten meat smell that
attract fly pollinators.
The following paragraphs describe typical chemical families
of compounds found in plant fragrances, with notes on human
perception of their scents. Most of these chemical families are
prominent in perfume compositions as well.
Terpenes
Figure 1
Examples of isoprenoid plant volatiles.
Figure 2
Examples of aliphatic and aromatic plant volatiles.
Figure 3
Examples of sulfur- and nitrogen-containing plant volatiles.
few functionalities like alcohol, aldehyde, or ester groups that
would allow dipole–dipole interactions or hydrogen bonds.
Therefore, the compounds have low boiling points and relatively high rates of evaporation, especially at elevated temperatures. The volatiles enter the gas phase and travel through the
air reaching the sensors of smell in animals or humans. Some
plants enhance the volatility of key compounds by heating
up during the flowering phase due to increased metabolic rates.
This increases the evaporation of volatiles that attract pollinators. A famous example is the corpse flower (Amorphophallus
titanum) whose giant inflorescence can heat up by more than
By far the largest group of plant volatiles comprises the family of
isoprenoids or terpenes. They are found in flower scents, in
various concentrations, and also as part of defensive mixtures
in leaf oils. The name ‘terpene’ is derived from ‘oil of turpentine,’ itself a mixture of terpenes isolated from pines with a characteristic odor. Terpene molecules are composed of five carbon
units, the isoprene units. Therefore, the total numbers of carbon
atoms in terpene structures are multiples of five. The majority of
volatile terpenes belong to the class of monoterpenes, with 10
carbons, thus composed of two isoprene units. The unique isoprenoid structure is the result of specific biosynthetic pathways
that lead from photosynthetically derived carbohydrates to
terpenes. Examples of common monoterpenes that are present
in different percentages in many floral and leaf scents are shown
in Figure 1. Their odors are generally perceived as pleasant by
humans. Functional groups like alcohol groups or keto groups
contribute to agreeable odor notes. Lavender (Lavendula spp.)
contains about 40% of linalool, 10% of eucalyptol (1,8cineole), small amounts of a-pinene, and a wealth of other
small amounts of volatiles, sometimes in traces only. Depending on the season and the cultivar, essential oils from the
strongly fragrant rose Rosa damascena, a major source of rose
oil, can contain around 20% of geraniol and 40% of citronellol,
also with the smell of rose, and smaller amounts, sometimes
traces only, of numerous other volatile compounds.
Many monoterpene molecules are asymmetric. (Chiral
centers are marked with * in Figure 1). Molecular asymmetries
often affect how we perceive the smells of these compounds. As
an example, (R)-()-linalool provides its woody lavender scent
to lavender and is the major odor component of lavender
herbs. Its enantiomer, (S)-(þ)-linalool, is found in coriander
and has a scent described as sweet floral. Plants may contain
one of the enantiomers exclusively or a racemic mixture of
both enantiomers. The oils from Eucalyptus spp. contain
racemic mixtures of both forms of a-pinene. Interestingly, the
volatile oils of North American pines contain one of the enantiomers of a-pinene, whereas most pine oils of European origin
have the other enantiomer.
A smaller group of isoprenoid volatiles comprises the sesquiterpenoids, with 15 carbons, the result of three isoprene
units. These molecules are still small enough to evaporate at
elevated temperatures. An example is caryophyllene, found in
cloves and in carnations, with its typical scent of cloves. Larger
terpene molecules, composed of four or more isoprenoid units,
are not volatile at ambient temperatures.
Aliphatic Alcohols, Aldehydes, and Esters
Aside from terpenes, simple aliphatic alcohols and aldehydes
are part of floral fragrances that are generally perceived as
pleasant by humans (see Figure 2). cis-3-Hexenol, a common
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Figure 4 Analysis of volatiles. (a) Schematic drawing of a gas chromatograph. (b) Gas chromatogram of a rose oil. Gas chromatogram by
Phenomenex, Inc.
plant volatile produced by many plants and also a common
perfume ingredient, has the smell of cut green grass. Octanal
is an aldehyde with a fruit-like odor that occurs naturally in
citrus oils. Esters are particularly present in ripe fruits, like ethyl
2-methylbutyrate in ripe apples, making them attractive to
feeding animals (as well as to people).
Aromatic Volatiles
Figure 5 Examples of natural and related synthetic volatiles for
perfumes.
While the aromatic volatiles described here (and shown in
Figure 2) are also aromatic in the sense of being pleasant
smelling compounds, aromatics in this context is understood
as compounds with a benzene ring. Benzyl acetate is a major
fragrance component in jasmine. Eugenol with a scent of cloves
and cinnamaldehyde with the smell of cinnamon both belong
to the subfamily of the phenyl propanoids, with C6eC3
structures.
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Sweet floral scents in general, as produced by mono- and
sesquiterpenes, aromatics, and simple aliphatic alcohols, aldehydes, and esters, attract pollinators like bees and butterflies.
Heavy sweet scents as from linalool attract moths. The
fragrances form when flowers open and combine with attractive colors and shapes to lure pollinators.
Sulfur- and Nitrogen-Containing Volatiles
Sulfur- and nitrogen-containing organic compounds (see
examples in Figure 3) contribute to plant odors that are attractive to flies, beetles, or fungus gnats, but because humans experience these odors as unpleasant they are of minor interest as
perfume components. Flowers or clusters of flowers that give
off these foul smells frequently have brown or maroon
pigments, resembling decomposing animal materials.
Sulfides and disulfides, like dimethyl disulfide, are part of
floral scents in the several types of plants appropriately named
corpse flowers (Rafflesia or Amorphophallus spp.). Flies and beetles
are their pollinators. The simple amine 1-aminohexane contributes to the slightly unpleasant floral odor of cow parsnip (Heracleum lanatum). Indole, part of the strong fragrance of hyacinths,
has itself a scent of feces (but exhibits a floral smell at very low
concentrations). In a mixture, such off-notes can contribute to
the characteristic bouquet of a floral scent, such as to the generally pleasant floral smell of hyacinths. Perfumers are well-aware
of off-notes lending characteristic notes to a perfume mixture.
Other Plant Volatiles
As an aside, many plant volatiles do not contribute to
fragrances nor are they of importance for the perfume industry,
but they have important functions in plants. Ethylene gas is one
of the plant hormones. Isoprene, composed of simple fivecarbon molecules, is released from the green foliage of many
trees. Some plants develop volatiles only when a plant is
injured, as a means of plant defense. Cyanogenic glycosides
release hydrogen cyanide when enzymatic action cleaves the
molecules (think biting into an apple seed), and the sulfurous
glucosinolates, present in plants of the cabbage family (Brassicaceae), release repellent volatile isothiocyanate and other
sulfur-containing compounds.
Isolation and Analysis of Plant Volatiles
Steam distillation has been the traditional method to isolate
volatiles from fragrant plant materials. Steam distillation and
the related hydrodiffusion technique are used to isolate the
essential oils from lavender or from rose petals. It is a suitable
method if plenty of plant material is available. The layer of
essential oils, floating on water, can be collected. Other isolation methods involve extraction with organic solvents, like
liquid hydrocarbons.
Plants often produce volatile oils in very small amounts. If
little plant material is available, as is often the case in research
on plant volatiles, the most sensitive method to collect and
analyze them is head-space analysis. Special glass bell jars, containing a probe with absorbents, are placed over the fragrant
plant parts. This method is nondestructive to volatiles and to
plant parts. The collected oils are eluted with appropriate
solvents from the probe and can be further analyzed by gas
chromatography (GC). This is a most sensitive analytical
method, used commonly not only in the analysis of plant volatiles but also in food analysis, crude oil analysis, and, of course,
analysis of perfumes. If combined with mass spectrometry
(MS), the identity of the single compounds in a mixture can
be determined by GC–MS. Figure 4 shows a schematic picture
of a gas chromatograph and the gas chromatogram of a rose oil,
each line in the chromatogram representing a different
compound. In a related method, used to evaluate the odor
contributions of the compounds in a volatile mixture, a ‘sniffing
port’ is attached to the exit port of the gas chromatograph. Each
compound can then be smelled as it is being separated and can
be further evaluated for its individual odor quality.
Different isolation methods affect the percentages of volatiles found in a fragrant mixture, for example, whether the volatiles were obtained by head-space analysis, a very sensitive
method, or by steam distillation.
The Human Sense of Smell
The previous descriptions of the various scents of plant volatiles are necessarily from a human perspective. It is difficult, if
not impossible, to give an exact description of a smell or
fragrance. We may use expressions like pleasant, sweet, strong,
or unpleasant. Looking ahead to the use of plant volatiles in
perfumes, the list of terms to describe the scents is vastly
expanded by professional perfumers. Following intense
training, they use a palette of expressions that include floral,
earthy, green, oriental, oceanic, mossy woods, mushroom,
musk, and more, to describe a fragrance. Most humans describe
the entire scent, the bouquet. A perceptive or well-trained
person may detect certain odor notes in a scent, like pine or
a lemon undertone. Often there is a dominant note, not necessarily due to the compound present in highest concentration in
a scent mixture. Character-impact compounds may have
a typical smell to us, even if in low concentrations. On the other
hand, some compounds in the volatile mixtures of plant scents
are without odor perception to humans, but may be recognized
by animals like insects. After all, plants did not evolve floral or
leaf scents to attract or deter humans.
The human sense of smell has a broad range of sensitivity to
several thousands of different scents. Our sense of smell is,
together with taste, our oldest sense in evolutionary terms. It
is affected by a person’s age, sex, and individual differences.
Our noses are capable of detecting lower concentrations of
volatiles than a gas chromatograph, currently our most sensitive analytical method. We are especially sensitive toward sulfurous odors for which the detection threshold is very low for
humans. This is why methyl mercaptan (CH3SH) is added to
cooking gas to alert the user to leaks. This sensitivity with
low-detection thresholds toward sulfurous and amine smells
may be an evolutionary result as decaying (rotting) meats
emanate these smells. Some mammals, like bears or dogs, are
well known for their much keener sense of smell, of course.
Some insects have extremely high sensitivity toward one or
a few specific compounds, as in the case of the sex pheromone
bombykol released by the female silkworm to attract mates.
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Volatiles for Perfumes
Flowers like roses and jasmine, leaves like lavender, fruits, seeds
like anise, some roots (ginger) as well as barks (cinnamon
bark), and some woods, as from pines, still provide large
amounts of fragrant plant materials for the perfume industry.
Therefore most of the volatile compounds described earlier
and the examples shown in Figures 1 and 2, namely the
terpenes, aliphatic alcohols, aldehydes, and esters, and the
aromatics, are also common perfume components.
Cultivating suitable plants and isolating their fragrances is
costly. Large amounts of plant materials are required to obtain
relatively small amounts of fragrant oils. In addition, fragrances
from natural sources are often not very stable and decompose
with light, moisture, or heat. Therefore, perfumes that contain
actual plant essences are expensive and luxury goods, as
expressed in the fancy bottles that contain them and the
beguiling brand names.
Currently about 90% of perfume materials are made
synthetically. A large percentage of scented materials are not
used in fine perfumes but in commercial products like soaps,
shampoos, bath oils, laundry soap, or cheaper perfumes, where
a full palette of natural fragrances is not needed. Natural plant
essences in products like laundry soap would not be stable. It
has also been found that about six to eight selected compounds
together can compose a satisfying desired fragrance for
a personal perfume, unlike the composition of a hundred or
more components in a natural plant fragrance.
Figures 5 and 6 show a selection of natural and synthetic
perfume ingredients. ‘Nature-identical’ compounds, although
also found naturally in plant (or animal) scents, are made at
lower costs synthetically from sources like wood, coal tar, or
petroleum. Furthermore, synthetic alterations of the chemical
structures of naturally occurring compounds can create more
stable fragrance components or compounds that do not have
health concerns, in addition to new fragrance notes. An example
is dihydrojasmone, a synthetic compound with the pleasant
odor note of jasmine, but more stable than the naturally occurring jasmone. As a further example, the compound vanillin gets
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oxidized easily and darkens when, for example, used in white
soap. Therefore, related synthetics, like UltravanilÒ (Figure 5),
have been developed that have higher stability.
Natural fragrances have been the inspiration for today’s
perfume compositions, including the addition of certain offnotes for a characteristic fragrance. The compounds muscone
and civetone (Figure 6), both with strong musky odors and
historically obtained from animal sources, have been used in
perfumery since ancient times, a custom that almost eradicated
the respective animals. Nowadays, the musks are produced
synthetically.
In 1888 A. Baur noticed the musky odor of products while
doing synthetic work on explosives related to trinitrotoluene
(TNT) and discovered the nitromusks (Figure 6). These
compounds are very different in structure from the natural
muscone and civetone. They were of high importance for
musky perfume notes till the 1950s, but their preparation
could be hazardous, and the compounds have phototoxic
properties. New, more stable compounds with musky scents
have been synthesized, and synthetic research is ongoing.
The inclusion of synthetic ingredients in perfumes became
fully acceptable with the launching of the still best-selling
perfume Chanel No. 5 in 1921 which, aside from natural oils
such as from rose and jasmine, includes also synthetic aliphatic
aldehydes. The mixture of all the components together leads to
the unique character of a perfume.
Desirable Properties of a Perfume
Perfumes are very complex mixtures. Composing successful
perfumes is an art, and perfumers who create them go through
in-depth schooling. Only a very small percentage of new
perfume creations make it onto the market.
A perfume needs to have some highly volatile fragrant ingredients that are smelled first when applied to the skin (the top
notes). Less volatile compounds, the middle or heart notes,
have to develop shortly after the top notes fade and should
last for several hours. The least volatile components, the base
notes, are the persisting odors (or what a garment smells like
long afterward). In a successful perfume all these notes must
blend harmoniously.
Aside from a desirable fragrance, an acceptable perfume
must have a lasting, pleasing color. It has to be reasonably
stable on skin and with skin secretions, and must not be allergenic nor have other health concerns. In addition, its price has
to be such that the consumer finds it fair for the product.
Isolation and Analysis of Perfume Ingredients
Figure 6 Natural and synthetic musks. Margareta Sequin, 2012. The
Chemistry of Plants - Perfumes, Pigments, and Poisons. RSC
Publishing, Cambridge, UK.
Three major types of isolation methods are used to obtain volatiles from plants, depending upon the stability of the plant materials and their fragrant compounds, namely expression, various
types of distillation, and extraction methods. Expression of the
essential oils, as from the peels of citrus fruits, is the simplest
technique. Among the distillation methods, dry distillation
involves high temperatures and can only be used to obtain volatiles from certain woods. Steam distillation, for example, of
lavender, produces what is called the essential oil in perfume
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industry. In steam distillation, the temperature is not above
100 C, but a subsequent separation of the layers of essential
oils from water is required. Solvent extractions of plant materials, with organic solvents like liquid hydrocarbons or ethyl
acetate, are most commonly used and have the advantage that
the processes take place at room temperature. They are used
when plant materials like jasmine flowers are too delicate for
steam distillation. Extraction with supercritical carbon dioxide
uses very low temperatures and as a further advantage leaves
no trace of solvents, but the necessary equipment is costly. The
products of extraction methods are called concrete. Absolutes
are obtained through extraction of the concrete with ethanol.
Absolutes are usually more concentrated than essential oils.
All the components of a perfume must be dissolved in
a solvent like alcohol, occasionally alcohol-water, in order to
keep the nonpolar fragrant oils in solution. Gas chromatography, often combined with mass spectrometry, is the leading
technique to determine the volatile components in perfumes.
It is a most important technique in the quality control of fragrant
mixtures and also a method to detect adulterated perfumes that
are sometimes sold fraudulently as natural ones. The methods
described in the following paragraph are used to detect fraud
and also to point out differences between natural plant scents
and artificial volatiles.
Fragrant oils from natural sources contain hundreds of
components, whereas the composition of a perfume from artificial compounds is a lot simpler, with few components, which
would be easily detected by a much lower number of peaks in
a gas chromatogram. Sometimes, perfume mixtures containing
natural oils are diluted with cheaper synthetic fragrances. Searching for by-products that can only be of synthetic origin can lead to
detection. Another method involves measuring the exact content
of radioactive carbon-14 (14C) in a sample. Plants absorb naturally occurring 14C through photosynthesis from the atmosphere
and incorporate it through biosynthesis into metabolites like
plant volatiles. If coal tar, with its radioactive 14C long decayed,
has been the source of synthetically made perfume components,
the resulting synthetic fragrances do not show this radioactivity.
History of Plant Volatiles for Perfumes
A visit to a perfume museum, like the Osmothèque in Versailles,
France, illustrates the long history of the use of fragrant plant
materials in human societies. People have ever been intrigued
by the scents and have worked at isolating them from plant
materials. Herbs, spices, and fragrant woods had been in use
in Egypt, Mesopotamia, India, and China thousands of years
ago. Extraction methods like pressing the essential oils of flower
petals onto fats to make pomades were known in ancient Egypt,
and lotions and perfumes were produced by extracting flowers
and leaves with alcohol. The fragrant resins frankincense and
myrrh were gifts of the Magi. Through the crusades and through
trading, the scented materials made their way west to Europe
and became items of luxury.
By the nineteenth century, chemists were adept at isolating
many compounds from the fragrant mixtures, using methods
like distillation and extraction. They successfully identified
many chemical structures of compounds found in the plant
scents. New synthetic methods were developed in order to
prove the structures by synthesis, and many of these methods
are still in use in different fields of chemistry. Two Nobel prizes
were awarded in connection with the exploration of biosynthetic pathways leading to isoprenoids, namely to O. Wallach
who proposed in 1887 that the molecules of many fragrant
plant compounds are hypothetically constructed from isoprene
units, and in 1939 to L. Ruzicka for his extensive research that
showed that plants follow distinct biosynthetic reaction pathways to assemble terpenes.
Conclusion
Plants and their volatiles have provided the inspiration for
perfume ingredients and continue to stimulate research on
new fragrant compounds. Synthetic methods are being developed to prepare volatiles with slightly altered structures that
have more desirable properties like higher stability. Altogether
new structures for volatiles are being investigated as well.
Most important is the cost efficiency of the production of
perfume ingredients. Many synthetic methods that were developed to produce new fragrant materials, especially with an eye
on creating more efficient syntheses with reduced production
costs, have led to the development of novel synthetic pathways
that are in use in other fields of synthetic chemistry as well. The
spectrum of new fragrances is continuously being expanded,
and volatiles for the perfume industry comprise a field of active
research.
Further Reading
Breitmaier, E., 2006. Terpenes: Flavors, Fragrances, Pharmaca, Pheromones. WileyVCH, Weinheim.
Brunke, E.J., Hammerschmidt, F.-J., Schmaus, G., 1994. Headspace analysis of
hyacinth flowers. Flavour Fragrance J. 9, 59–69.
Fortineau, A.-D., 2004. Chemistry perfumes your daily life. J. Chem. Educ. 81, 45–50.
Groom, N., 1997. The New Perfume Handbook, second ed. Blackie Academic and
Professional, London.
Herrmann, A. (Ed.), 2010. The Chemistry and Biology of Volatiles. Wiley, Hoboken.
Jalali-Heravi, M., Moazeni, R.S., Sereshti, H., 2011. Analysis of Iranian rosemary
essential oil: applications of gas chromatography-mass spectrometry combined
with chemometrics. J. Chromatogr. A 1218, 2569–2576.
Jirovetz, L., Buchbauer, G., Stoyanova, A., et al., 2005. Solid phase microextraction/
gas chromatographic and olfactory analysis of the scent and fixative properties of
the essential oil of Rosa damascena from China. Flavour Fragrance J. 20, 7–12.
Kaiser, R., 2006. Meaningful Scents around the World: Olfactory, Chemical, Biological,
and Cultural Considerations. Wiley-VCH, Weinheim.
Ohloff, G., Pickenhagen, W., Kraft, P., 2012. Scent and Chemistry: The Molecular
World of Odors. Wiley-VCH, Zürich: Verlag Helvetica Chimica Acta; Weinheim.
Pichersky, E., Gershenzon, J., 2002. The formation and function of plant volatiles:
perfumes for pollinator attraction and defense. Curr. Opin. Plant Biol. 5, 237–243.
Sell, C. (Ed.), 2006. The Chemistry of Fragrances: From Perfumer to Consumer,
second ed. The Royal Society of Chemistry, Cambridge, UK.
Séquin, M., 2012. The Chemistry of Plants: Perfumes, Pigments, and Poisons. The
Royal Society of Chemistry, Cambridge, UK.
Relevant Websites
http://www.ted.com/talks/luca_turin_on_the_science_of_scent.html – Luca Turin:
The Science of Scent.
http://www.fragrantica.com/news/Osmotheque-The-Perfume-Museum-2410.html –
Osmothèque Perfume Museum, Versailles.