Monoterpenes are a class of
terpene
Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n ≥ 2. Terpenes are major biosynthetic building blocks. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predomi ...
s that consist of two
isoprene
Isoprene, or 2-methyl-1,3-butadiene, is a common volatile organic compound with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. It is produced by many plants and animals (including humans) and its polymers ar ...
units and have the molecular formula C
10H
16. Monoterpenes may be linear (acyclic) or contain rings (monocyclic and bicyclic). Modified terpenes, such as those containing oxygen functionality or missing a methyl group, are called monoterpenoids. Monoterpenes and monoterpenoids are diverse. They have relevance to the pharmaceutical, cosmetic, agricultural, and food industries.
Biosynthesis
Monoterpenes are derived biosynthetically from units of
isopentenyl pyrophosphate
Isopentenyl pyrophosphate (IPP, isopentenyl diphosphate, or IDP) is an isoprenoid precursor. IPP is an intermediate in the classical, HMG-CoA reductase pathway (commonly called the mevalonate pathway) and in the ''non-mevalonate'' MEP pathway of i ...
, which is formed from
acetyl-CoA
Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidation, o ...
via the intermediacy of
mevalonic acid
Mevalonic acid (MVA) is a key organic compound in biochemistry; the name is a contraction of dihydroxymethylvalerolactone. The carboxylate anion of mevalonic acid, which is the predominant form in biological environments, is known as ''mevalonat ...
in the
HMG-CoA reductase pathway
The mevalonate pathway, also known as the isoprenoid pathway or HMG-CoA reductase pathway is an essential metabolic pathway present in eukaryotes, archaea, and some bacteria. The pathway produces two five-carbon building blocks called isopentenyl ...
. An alternative, unrelated biosynthesis pathway of IPP is known in some bacterial groups and the plastids of plants, the so-called MEP-(2-methyl-
D-erythritol-4-phosphate) pathway, which is initiated from
C5 sugars. In both pathways, IPP is isomerized to DMAPP by the enzyme isopentenyl pyrophosphate isomerase.
Geranyl pyrophosphate is the precursor to monoterpenes (and hence monoterpenoids).
Elimination of the pyrophosphate group from geranyl pyrophosphate leads to the formation of acyclic monoterpenes such as
ocimene
Ocimenes are a group of isomeric hydrocarbons. The ocimenes are monoterpenes found within a variety of plants and fruits. α-Ocimene and the two β-ocimenes differ in the position of the isolated double bond: it is terminal in the alpha isomer. ...
and the
myrcene
Myrcene, or β-myrcene, is a terpene, monoterpene. A colorless oil, it occurs widely in essential oils. It is produced mainly semi-synthetically from ''Myrcia'', from which it gets its name. It is an intermediate in the production of several frag ...
s. Hydrolysis of the phosphate groups leads to the prototypical acyclic monoterpenoid
geraniol
Geraniol is a monoterpenoid and an alcohol. It is the primary component of citronella oil and is a primary component of rose oil and palmarosa oil. It is a colorless oil, although commercial samples can appear yellow. It has low solubility i ...
. Additional rearrangements and oxidations provide compounds such as
citral
Citral is an acyclic monoterpene aldehyde. Being a monoterpene, it is made of two isoprene units. Citral is a collective term which covers two geometric isomers that have their own separate names; the ''E''-isomer is named geranial (''trans''- ...
,
citronellal,
citronellol,
linalool
Linalool () refers to two enantiomers of a naturally occurring terpene alcohol found in many flowers and spice plants. Together with geraniol, nerol, and citronellol, linalool is one of the rose alcohols. Linalool has multiple commercial app ...
, and many others. Many monoterpenes found in marine organisms are
halogen
The halogens () are a group in the periodic table consisting of six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the radioactive elements astatine (At) and tennessine (Ts), though some authors would ...
ated, such as
halomon
Halomon is a polyhalogenated monoterpene first isolated from the marine red algae '' Portieria hornemannii''. Halomon has attracted research interest because of its promising profile of selective cytotoxicity that suggests its potential use as a ...
.
Main examples
Myrcen.png, Myrcene
Myrcene, or β-myrcene, is a terpene, monoterpene. A colorless oil, it occurs widely in essential oils. It is produced mainly semi-synthetically from ''Myrcia'', from which it gets its name. It is an intermediate in the production of several frag ...
is an acyclic monoterpene, an alkene
In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins.
The Internationa ...
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...
Menthol_skeletal.svg, Menthol
Menthol is an organic compound, specifically a Monoterpene, monoterpenoid, that occurs naturally in the oils of several plants in the Mentha, mint family, such as Mentha arvensis, corn mint and peppermint. It is a white or clear waxy crystallin ...
is a monocyclic monoterpenoid
Limonene-2D-skeletal.svg, Limonene
Limonene () is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the essential oil of citrus fruit peels. The (+)-isomer, occurring more commonly in nature as the fragrance of oranges, ...
is a monocyclic monoterpene
Carvone.svg, Carvone
Carvone is a member of a family of chemicals called terpenoids. Carvone is found naturally in many essential oils, but is most abundant in the oils from seeds of caraway (''Carum carvi''), spearmint (''Mentha spicata''), and dill.
Uses Food appli ...
is a monoterpenoid
Beta-thujaplicin.png, Hinokitiol
Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae. It is a tropolone derivative and one of the thujaplicins. Hinokitiol is used in oral and skin care products, and is a food additive us ...
is a monoterpenoid, a tropolone
Tropolone is an organic compound with the chemical formula . It is a pale yellow solid that is soluble in organic solvents. The compound has been of interest to research chemists because of its unusual electronic structure and its role as a liga ...
derivative
Linalool_skeletal.svg, Linalool
Linalool () refers to two enantiomers of a naturally occurring terpene alcohol found in many flowers and spice plants. Together with geraniol, nerol, and citronellol, linalool is one of the rose alcohols. Linalool has multiple commercial app ...
is an acyclic monoterpenoid
Bicyclic monoterpenes include
carene,
sabinene
Sabinene is a natural bicyclic monoterpene with the molecular formula C10H16. It is isolated from the essential oils of a variety of plants including Marjoram, holm oak (''Quercus ilex'') and Norway spruce (''Picea abies''). It has a strained ...
,
camphene
Camphene is a bicyclic organic compound. It is one of the most pervasive monoterpenes. As with other terpenes, it is insoluble in water, flammable, colorless, and has a pungent smell. It is a minor constituent of many essential oils such as tu ...
, and
thujene
Thujene (or α-thujene) is a natural organic compound classified as a monoterpene. It is found in the essential oils of a variety of plants, and contributes pungency to the flavor of some herbs such as Summer savory.''PDR for Herbal Medicines'', ...
.
Camphor
Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel (''Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the kapu ...
,
borneol
Borneol is a bicyclic organic compound and a terpene derivative. The hydroxyl group in this compound is placed in an '' endo'' position. The exo diastereomer is called isoborneol. Being chiral, borneol exists as enantiomers, both of which are fou ...
,
eucalyptol
Eucalyptol (also called cineole) is a monoterpenoid colorless liquid, and a bicyclic ether. It has a fresh camphor-like odor and a spicy, cooling taste. It is insoluble in water, but miscible with organic solvents. Eucalyptol makes up about ...
and
ascaridole
Ascaridole is a natural organic compound classified as a bicyclic monoterpenoid that has an unusual bridging organic peroxide, peroxide functional group. It is a colorless liquid with a pungent smell and taste that is soluble in most organic solve ...
are examples of bicyclic monoterpenoids containing ketone, alcohol, ether, and bridging
peroxide
In chemistry, peroxides are a group of Chemical compound, compounds with the structure , where the R's represent a radical (a portion of a complete molecule; not necessarily a free radical) and O's are single oxygen atoms. Oxygen atoms are joined ...
functional groups, respectively.
Umbellulone
Umbellulone is a headache-inducing monoterpene ketone found in the leaves of the tree '' Umbellularia californica'', sometimes known as the "headache tree".
It is hypothesized to cause headaches by influencing the trigeminovascular system via TRP ...
is another example of bicyclic monoterpene ketone.
Natural roles
Monoterpenes are found in many parts of different plants, such as
barks,
heartwood
Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...
, bark and leaves of coniferous trees, in
vegetable
Vegetables are edible parts of plants that are consumed by humans or other animals as food. This original meaning is still commonly used, and is applied to plants collectively to refer to all edible plant matter, including edible flower, flo ...
s,
fruit
In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering.
Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...
s and
herb
Herbs are a widely distributed and widespread group of plants, excluding vegetables, with savory or aromatic properties that are used for flavoring and garnishing food, for medicinal purposes, or for fragrances. Culinary use typically distingu ...
s.
Essential oil
An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the ...
s are very rich in monoterpenes. Several monoterpenes produced by trees, such as
linalool
Linalool () refers to two enantiomers of a naturally occurring terpene alcohol found in many flowers and spice plants. Together with geraniol, nerol, and citronellol, linalool is one of the rose alcohols. Linalool has multiple commercial app ...
,
hinokitiol
Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae. It is a tropolone derivative and one of the thujaplicins. Hinokitiol is used in oral and skin care products, and is a food additive us ...
, and
ocimene
Ocimenes are a group of isomeric hydrocarbons. The ocimenes are monoterpenes found within a variety of plants and fruits. α-Ocimene and the two β-ocimenes differ in the position of the isolated double bond: it is terminal in the alpha isomer. ...
have
fungicidal
Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...
and
antibacterial
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...
activities and participate in wound healing. Some of these compounds are produced to protect the trees from
insect
Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...
attacks.
Monoterpenes are emitted by
forest
A forest is an ecosystem characterized by a dense ecological community, community of trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, ...
s and form
aerosol
An aerosol is a suspension (chemistry), suspension of fine solid particles or liquid Drop (liquid), droplets in air or another gas. Aerosols can be generated from natural or Human impact on the environment, human causes. The term ''aerosol'' co ...
s that are proposed to serve as
cloud condensation nuclei
Cloud condensation nuclei (CCNs), also known as cloud seeds, are small particles typically 0.2 μm, or one hundredth the size of a cloud droplet. CCNs are a unique subset of aerosols in the atmosphere on which water vapour condenses. This c ...
(CCN). Such aerosols can increase the brightness of clouds and cool the climate.
Many monoterpenes have unique smell and flavor. For example,
sabinene
Sabinene is a natural bicyclic monoterpene with the molecular formula C10H16. It is isolated from the essential oils of a variety of plants including Marjoram, holm oak (''Quercus ilex'') and Norway spruce (''Picea abies''). It has a strained ...
contributes to the
spicy
Pungency ( ) is the taste of food commonly referred to as spiciness, hotness or heat, found in foods such as chili peppers. Highly pungent tastes may be experienced as unpleasant. The term piquancy ( ) is sometimes applied to foods with a lower ...
taste of
black pepper
Black pepper (''Piper nigrum'') is a flowering vine in the family Piperaceae, cultivated for its fruit (the peppercorn), which is usually dried and used as a spice and seasoning. The fruit is a drupe (stonefruit) which is about in diameter ...
,
3-carene gives
cannabis
''Cannabis'' () is a genus of flowering plants in the family Cannabaceae that is widely accepted as being indigenous to and originating from the continent of Asia. However, the number of species is disputed, with as many as three species be ...
an earthy taste and smell,
citral
Citral is an acyclic monoterpene aldehyde. Being a monoterpene, it is made of two isoprene units. Citral is a collective term which covers two geometric isomers that have their own separate names; the ''E''-isomer is named geranial (''trans''- ...
has a lemon-like pleasant odor and contributes to the distinctive smell of
citrus
''Citrus'' is a genus of flowering trees and shrubs in the family Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, mandarins, lemons, grapefruits, pomelos, and limes.
''Citrus'' is nativ ...
fruits, and
thujene
Thujene (or α-thujene) is a natural organic compound classified as a monoterpene. It is found in the essential oils of a variety of plants, and contributes pungency to the flavor of some herbs such as Summer savory.''PDR for Herbal Medicines'', ...
and
carvacrol
Carvacrol, or cymophenol, C6H3(CH3)(OH)C3H7, is a monoterpene, monoterpenoid phenol. It has a characteristic pungent, warm odor of oregano.
Natural occurrence
Carvacrol is present in the essential oil of ''Origanum vulgare'' (oregano), oil of t ...
are responsible for the
pungent
Pungency ( ) is the taste of food commonly referred to as spiciness, hotness or heat, found in foods such as chili peppers. Highly pungent tastes may be experienced as unpleasant. The term piquancy ( ) is sometimes applied to foods with a lower ...
flavors of
summer savory
Summer savory (''Satureja hortensis'') is among the best known of the Satureja, savory genus. It is an annual, but otherwise is similar in use and flavor to the perennial winter savory. It is used more often than winter savory, which has a sligh ...
and
oregano
Oregano (, ; ''Origanum vulgare'') is a species of flowering plant in the mint family, Lamiaceae. It was native to the Mediterranean region, but widely naturalised elsewhere in the temperate climate, temperate Northern Hemisphere.
Oregano is a ...
, respectively.
Monoterpenes are considered
allelochemicals.
Uses
Many monoterpenes are
volatile compounds and some of them are well-known
fragrants found in the
essential oil
An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the ...
s of many plants. For example,
camphor
Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel (''Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the kapu ...
,
citral
Citral is an acyclic monoterpene aldehyde. Being a monoterpene, it is made of two isoprene units. Citral is a collective term which covers two geometric isomers that have their own separate names; the ''E''-isomer is named geranial (''trans''- ...
,
citronellol,
geraniol
Geraniol is a monoterpenoid and an alcohol. It is the primary component of citronella oil and is a primary component of rose oil and palmarosa oil. It is a colorless oil, although commercial samples can appear yellow. It has low solubility i ...
,
grapefruit mercaptan
Grapefruit mercaptan is a natural organic compound found in grapefruit. It is a monoterpenoid that contains a thiol (also known as a mercaptan) functional group. Structurally a hydroxy group of terpineol is replaced by the thiol in grapefruit m ...
,
eucalyptol
Eucalyptol (also called cineole) is a monoterpenoid colorless liquid, and a bicyclic ether. It has a fresh camphor-like odor and a spicy, cooling taste. It is insoluble in water, but miscible with organic solvents. Eucalyptol makes up about ...
,
ocimene
Ocimenes are a group of isomeric hydrocarbons. The ocimenes are monoterpenes found within a variety of plants and fruits. α-Ocimene and the two β-ocimenes differ in the position of the isolated double bond: it is terminal in the alpha isomer. ...
,
myrcene
Myrcene, or β-myrcene, is a terpene, monoterpene. A colorless oil, it occurs widely in essential oils. It is produced mainly semi-synthetically from ''Myrcia'', from which it gets its name. It is an intermediate in the production of several frag ...
,
limonene
Limonene () is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the essential oil of citrus fruit peels. The (+)-isomer, occurring more commonly in nature as the fragrance of oranges, ...
,
linalool
Linalool () refers to two enantiomers of a naturally occurring terpene alcohol found in many flowers and spice plants. Together with geraniol, nerol, and citronellol, linalool is one of the rose alcohols. Linalool has multiple commercial app ...
,
menthol
Menthol is an organic compound, specifically a Monoterpene, monoterpenoid, that occurs naturally in the oils of several plants in the Mentha, mint family, such as Mentha arvensis, corn mint and peppermint. It is a white or clear waxy crystallin ...
,
camphene
Camphene is a bicyclic organic compound. It is one of the most pervasive monoterpenes. As with other terpenes, it is insoluble in water, flammable, colorless, and has a pungent smell. It is a minor constituent of many essential oils such as tu ...
and
pinene
Pinene is a collection of unsaturated bicyclic monoterpenes. Two geometric isomers of pinene are found in nature, α-pinene and β-pinene. Both are chiral. As the name suggests, pinenes are found in pines. Specifically, pinene is the major comp ...
s are used in
perfume
Perfume (, ) is a mixture of fragrance, fragrant essential oils or aroma compounds (fragrances), Fixative (perfumery), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agre ...
s and
cosmetic products.
Limonene
Limonene () is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the essential oil of citrus fruit peels. The (+)-isomer, occurring more commonly in nature as the fragrance of oranges, ...
and
perillyl alcohol are used in
cleaning
Cleaning is the process of removing unwanted substances, such as dirt, infectious agents, and other impurities, from an object or environment. Cleaning is often performed for beauty, aesthetic, hygiene, hygienic, Function (engineering), function ...
products.
Many monoterpenes are used as food
flavors and
food additive
Food additives are substances added to food to preserve flavor or enhance taste, appearance, or other sensory qualities. Some additives, such as vinegar ( pickling), salt ( salting), smoke ( smoking) and sugar ( crystallization), have been used f ...
s, such as
bornyl acetate,
citral
Citral is an acyclic monoterpene aldehyde. Being a monoterpene, it is made of two isoprene units. Citral is a collective term which covers two geometric isomers that have their own separate names; the ''E''-isomer is named geranial (''trans''- ...
,
eucalyptol
Eucalyptol (also called cineole) is a monoterpenoid colorless liquid, and a bicyclic ether. It has a fresh camphor-like odor and a spicy, cooling taste. It is insoluble in water, but miscible with organic solvents. Eucalyptol makes up about ...
,
menthol
Menthol is an organic compound, specifically a Monoterpene, monoterpenoid, that occurs naturally in the oils of several plants in the Mentha, mint family, such as Mentha arvensis, corn mint and peppermint. It is a white or clear waxy crystallin ...
,
hinokitiol
Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae. It is a tropolone derivative and one of the thujaplicins. Hinokitiol is used in oral and skin care products, and is a food additive us ...
,
camphene
Camphene is a bicyclic organic compound. It is one of the most pervasive monoterpenes. As with other terpenes, it is insoluble in water, flammable, colorless, and has a pungent smell. It is a minor constituent of many essential oils such as tu ...
and
limonene
Limonene () is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the essential oil of citrus fruit peels. The (+)-isomer, occurring more commonly in nature as the fragrance of oranges, ...
.
Menthol
Menthol is an organic compound, specifically a Monoterpene, monoterpenoid, that occurs naturally in the oils of several plants in the Mentha, mint family, such as Mentha arvensis, corn mint and peppermint. It is a white or clear waxy crystallin ...
,
hinokitiol
Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae. It is a tropolone derivative and one of the thujaplicins. Hinokitiol is used in oral and skin care products, and is a food additive us ...
and
thymol
Thymol (also known as 2-isopropyl-5-methylphenol, IPMP), , is a toxic monoterpenoid phenol derivative of ''p''-Cymene, isomeric with carvacrol. It occurs naturally in the oil of thyme, and it is extracted from ''Thymus vulgaris'' (common thy ...
are also used in
oral hygiene
Oral hygiene is the practice of keeping one's oral cavity clean and free of disease and other problems (e.g. bad breath) by regular brushing of the teeth (dental hygiene) and adopting good hygiene habits. It is important that oral hygiene be carr ...
products.
Thymol
Thymol (also known as 2-isopropyl-5-methylphenol, IPMP), , is a toxic monoterpenoid phenol derivative of ''p''-Cymene, isomeric with carvacrol. It occurs naturally in the oil of thyme, and it is extracted from ''Thymus vulgaris'' (common thy ...
also has
antiseptic
An antiseptic ( and ) is an antimicrobial substance or compound that is applied to living tissue to reduce the possibility of sepsis, infection, or putrefaction. Antiseptics are generally distinguished from ''antibiotics'' by the latter's abil ...
and
disinfectant
A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than ...
properties.
Volatile monoterpenes produced by plants can attract or repel insects, thus some of them are used in
insect repellent
An insect repellent (also commonly called "bug spray" or "bug deterrent") is a substance applied to the skin, clothing, or other surfaces to discourage insects (and arthropods in general) from landing or climbing on that surface. Insect repellent ...
s, such as
citronellol,
eucalyptol
Eucalyptol (also called cineole) is a monoterpenoid colorless liquid, and a bicyclic ether. It has a fresh camphor-like odor and a spicy, cooling taste. It is insoluble in water, but miscible with organic solvents. Eucalyptol makes up about ...
,
limonene
Limonene () is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the essential oil of citrus fruit peels. The (+)-isomer, occurring more commonly in nature as the fragrance of oranges, ...
,
linalool
Linalool () refers to two enantiomers of a naturally occurring terpene alcohol found in many flowers and spice plants. Together with geraniol, nerol, and citronellol, linalool is one of the rose alcohols. Linalool has multiple commercial app ...
,
hinokitiol
Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae. It is a tropolone derivative and one of the thujaplicins. Hinokitiol is used in oral and skin care products, and is a food additive us ...
,
menthol
Menthol is an organic compound, specifically a Monoterpene, monoterpenoid, that occurs naturally in the oils of several plants in the Mentha, mint family, such as Mentha arvensis, corn mint and peppermint. It is a white or clear waxy crystallin ...
and
thymol
Thymol (also known as 2-isopropyl-5-methylphenol, IPMP), , is a toxic monoterpenoid phenol derivative of ''p''-Cymene, isomeric with carvacrol. It occurs naturally in the oil of thyme, and it is extracted from ''Thymus vulgaris'' (common thy ...
.
Ascaridole
Ascaridole is a natural organic compound classified as a bicyclic monoterpenoid that has an unusual bridging organic peroxide, peroxide functional group. It is a colorless liquid with a pungent smell and taste that is soluble in most organic solve ...
,
camphor
Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel (''Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the kapu ...
and
eucalyptol
Eucalyptol (also called cineole) is a monoterpenoid colorless liquid, and a bicyclic ether. It has a fresh camphor-like odor and a spicy, cooling taste. It is insoluble in water, but miscible with organic solvents. Eucalyptol makes up about ...
are monoterpenes that have pharmaceutical use.
Health effects
A study suggests that a range of
floor cleaners with certain monoterpenes may cause indoor
air pollution
Air pollution is the presence of substances in the Atmosphere of Earth, air that are harmful to humans, other living beings or the environment. Pollutants can be Gas, gases like Ground-level ozone, ozone or nitrogen oxides or small particles li ...
equivalent or exceeding the harm to respiratory tracts when the time is spent
near a busy road. This is due to
ozonolysis
In organic chemistry, ozonolysis is an organic reaction where the Saturated and unsaturated compounds, unsaturated bonds are Bond cleavage, cleaved with ozone (). Multiple carbon–carbon bond are replaced by carbonyl () groups, such as aldehydes ...
of monoterpenes like
limonene
Limonene () is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the essential oil of citrus fruit peels. The (+)-isomer, occurring more commonly in nature as the fragrance of oranges, ...
leading to the production of atmospheric
SOA. Another study suggests monoterpenes substantially affect ambient organic aerosol with uncertainties regarding environmental impacts. In a review, scientists concluded that they hope that these "substances will be extensively studied and used in more and more in medicine". A 2013 study found that "Based on adverse effects and risk assessments, d-limonene may be regarded as a safe ingredient. However, the potential occurrence of skin irritation necessitates regulation of this chemical as an ingredient in cosmetics." According to a review, several studies showed "that some monoterpenes (e.g., pulegone, menthofuran, camphor, and limonene) and sesquiterpenes (e.g., zederone, germacrone) exhibited liver toxicity" and that i.a. intensive research on terpenes toxicity is needed.
See also
*
Terpene
Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n ≥ 2. Terpenes are major biosynthetic building blocks. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predomi ...
*
Terpenoid
The terpenoids, also known as isoprenoids, are a class of naturally occurring organic compound, organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeabl ...
*
Diterpene
Diterpenes are a class of terpenes composed of four isoprene units, often with the molecular formula C20H32. They are biosynthesized by plants, animals and fungi via the HMG-CoA reductase pathway, with geranylgeranyl pyrophosphate being a primary ...
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Sesquiterpene
Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be cyclic or contain rings, including many combinations. Biochemical modifications s ...
References
{{Terpenoids
Monoterpenes
Terpenes and terpenoids
Wood extracts