The carbon chain may be fully saturated or unsaturated (with double and/or triple bonds), it may also be  substituted with chlorine, bromine or sulfate groups. Some acetylenic alcohols have been also described.

• Saturated alcohols

• Unsaturated alcohols

• Acetylenic alcohols

• Sulfated alcohols
  

- Saturated alcohols

Among the most common, some are listed below

Formula	Normal alcohols	Iso-alcohols	Anteiso-alcohols
C12H25OH	1-dodecanol (lauryl alcohol)	10-methyl-1-hendecanol (isolauryl alcohol)	9-methyl-1-hendecanol (anteisolauryl alcohol)
C14H29OH	1-tetradecanol (myristyl alcohol)	12-methyl-1-tridecanol (isomyristyl alcohol)	11-methyl-1-tridecanol (anteisomyristyl alcohol)
C16H33OH	1-hexadecanol (cetyl alcohol)	14-methyl-1-pentadecanol (isopalmityl alcohol)	13-methyl-1-pentadecanol (anteisopalmityl alcohol)
C18H37OH	1-octadecanol (stearyl alcohol)	16-methyl-1-heptadecanol (isostearyl alcohol)	15-methyl-1-pentadecanol (anteisostearyl alcohol)

Various fatty alcohols are found in the waxy film that plants have over their leaves and fruits. Among them, octacosanol (C28:0) is the most frequently cited.
Policosanol is a natural mixture of higher primary aliphatic alcohols isolated and purified from sugar cane (Saccharum officinarum, L.) wax, whose main component is octacosanol  but contains also hexacosanol (C26:0) and triacontanol or melissyl alcohol (C30:0). This mixture was shown to have cholesterol-lowering effects in rabbits (Arruzazabala ML et al., Biol Res 1994, 27, 205). Octacosanol was also able to suppress lipid accumulation in rats fed on a high-fat diet (Kato S et al., Br J Nutr 1995, 73, 433) and to inhibit platelet aggregation (Arruzazabala ML et al., Thromb Res 1993, 69, 321). The effectiveness of policosanol is still questionable. More recent studies in mice question about any action on improvement of lipoprotein profiles (Dullens SPJ et al., J Lipid Res 2008, 49, 790). The authors conclude that individual policosanols, as well as natural policosanol mixtures, have no potential for reducing coronary heart disease risk through effects on serum lipoprotein concentrations. Furthermore, sugar cane policosanol at doses of 20 mg daily has shown no lipid lowering effects in subjects with primary hypercholesterolemia (Francini-Pesenti F et al., Phytother Res 2008, 22, 318).

Many alcohols in the C10 to C18 range, and their short-chain acid esters are potent sex or aggregation pheromones. They are mainly found as components of specialized defensive glands, pheromone glands or glands of the reproductive system.

A series of C22 up to C28 saturated n-alcohols, with even carbon numbers predominating, and a maximum at C26 and C28, has been identified in the cyanobacterium Anabaena cylindrica (Abreu-Grobois FA et al., Phytochemistry 1977, 16, 351). Several authors have reported high contents of the 22:0 alcohol in sediments where an algal origin is plausible. For example, the major alcohol in a sample of the lacustrine Green River Shale of Eocene age is also 22:0 which comprises over 50% of the alcohols present (Sever JR et al., Science 1969, 164, 1052)

Long-chain alcohols are known as major surface lipid components (waxes) with chains from C20 up to C34 carbon atoms, odd carbon-chain alcohols being found in only low amounts. Very long-chain methyl-branched alcohols (C38 to C44) and their esters with short-chain acids were shown to be present in insects, mainly during metamorphosis. A series of long-chain alkanols (more than 23 carbon atoms) were identified in settling particles and surface sediments from Japanese lakes and were shown to be produced by planktonic bacteria being thus useful molecular markers (Fukushima K et al., Org Geochem 2005, 36, 311).
Cutin and suberin contain as monomer saturated alcohols from C16 to C22 up to 8% of the total polymers. C18:1 alcohol (oleyl alcohol) is also present.

Long-chain di-alcohols (1,3-alkanediols) have been described in the waxes which impregnate the matrix covering all organs of plants (Vermeer CP et al., Phytochemistry 2003, 62, 433). These compounds forming about 11% of the leaf cuticular waxes of Ricinus communis were identified as homologous unbranched alcohols ranging from C22 to C28 with hydroxyl group at the carbon atoms 1 and 3. 
In the leaf cuticular waxes of Myricaria germanica (Tamaricaceae) several alkanediols were identified (Jetter R, Phytochemistry 2000, 55, 169). Hentriacontanediol (C31) with one hydroxyl group in the 12-position and the second one in positions from 2 to 18 is the most abundant diol (9% of the wax). Others were far less abundant : C30-C34 alkanediols with one hydroxyl group on a primary and one on a secondary carbon atom, C25-C43 b-diols and C39-C43 g-diols. Very-long-chain 1,5-alkanediols ranging from C28 to C38, with strong predominance of even carbon numbers, were identified in the cuticular wax of Taxus baccata (Wen M et al., Phytochemistry 2007, 68, 2563). The predominant diol had 32 carbon atoms (29% of the total).
Long-chain saturated C30-C32 diols occur in most marine sediments and in a few instances, such as in Black Sea sediments, they can be the major lipids (de Leeuw JW et al., Geochim Cosmochim Acta 1981, 45, 2281). A microalgal source for these compounds was discovered when Volkman JK et al. (Org Geochem 1992, 18, 131) identified C30-C32 diols in marine eustigmatophytes from the genus Nannochloropsis. 

- Unsaturated alcohols

Some fatty alcohols have one double bond (monounsaturated). Their general formula is:

CH₃(CH₂)_xCH=CH(CH₂)_y-CH₂OH

The unique double bond may be found in different positions: at the C6: i.e. cis-6-octadecen-1-ol (petroselenyl alcohol), C9 i.e cis-9-octadecen-1-ol (oleyl alcohol) and C11 i.e cis-11-octadecen-1-ol (vaccenyl alcohol). Some of these alcohols have insect pheromone activity. As an example, 11-eicosen-1-ol is a major component of the alarm pheromone secreted by the sting apparatus of the worker honeybee. 
An acetoxy derivative of a 16-carbon alcohol with one double bond, gyptol (10-acetoxy cis-7-hexadecen-1-ol), was described to be a strong attractive substance secreted by a female moth (Porthetria dispar, "gypsy moth").

A fatty alcohol with two double bonds, bombykol (tr-10,cis-12-hexadecadien-1-ol), was also shown to be excreted as a very strong attractive substance by the female of silk-worm (Bombyx mori). 

This first discovery of a pheromone was made by Butenandt A et al. (Z Naturforsch 1959, 14, 283) who was formerly Nobel laureate (in 1939) for his work in sex hormones. Another pheromone, 8,10-dodecadienol (codlemone), is secreted by the codling moth Cydia pomonella, has been used for monitoring and mating in apple and pear orchards in the USA and Europe. This molecule was also used to monitor the population of the pea moth Cydia nigricana. Likewise, 7,9-dodecadienol, the female pheromone of the European grapewine moth Lobesia botrana, was used to control this important pest in vineyards. 
A fatty triol with one double bond, avocadene (16-heptadecene-1,2,4-triol) is found in avocado fruit (Persea americana) and has been tested for anti-bacterial and anti-inflammatory properties. These properties are likely related with the curative effects of avocado described for a number of ailments (diarrhea, dysentery, abdominal pains and high blood pressure).
Long-chain alkenols (C37 to C39) with 2 to 4 double bonds, the reduced form of the alkenones, have been described in the benthic haptophyte Chrysotila lamellosa (Rontani JF et al., Phytochemistry 2004, 65, 117). al., 1986). C30 to C32 alcohols having one or two double bonds are significant constituents of the lipids of marine eustigmatophytes of the genus Nannochloropsis (Volkman JK et al., Org Geochem 1992, 18, 131). These microalgae could be partially the source of the alkenols found in some marine sediments. 

Two chlorinated derivatives of unusual alcohols were described in a red alga Gracilaria verrucosa (Shoeb M et al., J Nat Prod 2003, 66, 1509). Both compounds have a C12 aliphatic chain chlorinated in position 2 and with one double bond at carbon 2 (compound 1 : 2-chlorododec-2-en-1-ol) or two double bonds at carbon 2 and 11 (compound 2 : 2-chlorododec-2,11-dien-1-ol). 

- Acetylenic alcohols 

Natural acetylenic alcohols and their derivatives have been isolated from a wide variety of plant species, fungi and invertebrates. Pharmacological studies have revealed that many of them display chemical and medicinal properties.

Monoacetylenic alcohols : were isolated from culture of Clitocybe catinus (Basidiomycetes) and the study of their structure revealed the presence of two or three hydroxyl groups (Armone A et al., Phytochemistry 2000, 53, 1087). One of these compounds is shown below.

Acetylenic alcohols have been also described in a tropical sponge Reniochaline sp (Lee HS et al., Lipids 2009, 44, 71). One of the two described in that species is shown below, it exhibited a significant growth effect against human tumor cell lines.

Polyacetylenic alcohols : Several examples with different chain lengths, unsaturation degrees, and substitution have been reported from terrestrial plants and marine organisms. Food plants of the Apiaceae (Umbellifereae) plant family such as carrots, celery and parsley, are known to contain several bioactive polyacetylenes. The main plant sources of these compounds are Angelica dahurica, Heracleum sp and Crithmum maritimum (falcarindiol, falcarinol),  red ginseng (Panax ginseng) (panaxacol, panaxydol, panaxytriol), Cicuta virosa (virol A), and Clibadium sylvestre (cunaniol). All these compounds display antibiotic or cytotoxic activities.

Many other polyacetylenic alcohols were found in primitive marine organisms, such as sponges and ascidians. These invertebrates have no physical defenses and thus they have developed efficient chemical mechanisms such as polyacetylenic metabolites to resist predators and bacteria. 
 
A C36 linear diacetylene alcohol named lembehyne was found in an Indonesian marine sponge (Haliclona sp) (Aoki S et al., Tetrahedron 2000, 56, 9945) and was later able to induce neuronal differentiation in neuroblastoma cell (Aoki S et al., Biochem Biophys Res Comm 2001, 289, 558). 

Several polyacetylenic alcohols with 22 carbon atoms were isolated and identified in lipid extract from a Red Sea sponge, Callyspongia sp (Youssef DT et al., J Nat Prod 2003, 66, 679). Their physical study revealed the presence of 4 triple bonds and one, two or three double bonds. The structure of one of these Callyspongenols is given below.  

Several di- and tri-acetylenic di-alcohols with a chain of 26 up to 31 carbon atoms, named strongylodiols, have been isolated from a Petrosia Okinawan marine sponge (Watanabe K et al., J Nat Prod 2005, 68, 1001). Some of them have cytotoxic properties.   

Several polyacetylenic alcohols with 21 carbon atoms were isolated from a marine ascidian (Polyclinidae) and were determined to have two triple bonds combined with a conjugated dienyne group (Gavagnin M et al., Lipids 2004, 39, 681). Some of them have an additional hydroxyl group or only three double bonds. The structure of one of these molecules is given below.  

- Sulfated alcohols

  Long-chain di-hydroxy alcohols in which both the primary and secondary hydroxyl groups are converted to sulfate esters and one to five chlorine atoms are introduced at various places have been discovered in the alga Ochromonas danica (Chrysophyceae, Chrysophyta) where they constitute 15% of the total lipids (Haines TH, Biochem J 1969, 113, 565). An example of these chlorosulfolipids is given below. There may be several types of chlorine addition : one at R₄, two at R₃ and R₅ or R₁ and R₂, five at R₁ to R₅ and six at R₁ to R₆.  

Similar molecules with a 24 carbon chain was also described in Ochromonas malhamensis (review in Dembitsky VM et al., Prog Lipid Res 2002, 41, 315). It was suggested that the chlorosulfolipids replace sulfoquinovosyl diglyceride, since when the later is high the former is low and vice versa.

 Several of these chlorosulfolipids have also been identified from more than 30 species of both freshwater and marine algae belonging to green (Chlorophyceae), brown (Phaeophyceae), red (Rhodophyceae) macrophytic algae (Mercer EI et al., Phytochemistry 1979, 18, 457), and other microalgal species (Mercer EI et al., Phytochemistry 1975, 14, 1545).

2 - Branched-chain alcohols

Among the most important saturated isopranols found in plants or in geological sediments are those having two (tetrahydrogeraniol), three (farnesanol), or four (phytanol) isoprenoid units. Pristanol (2,6,10,14-tetramethyl-1-pentadecanol) is tetramethylated but with only three complete isoprenoid units.

B -  Unsaturated polyisoprenoids (prenols or polyprenols) 

They have the following general structure :

These isoprenoid alcohols are also known as terpenols. Search for polyisoprenoid alcohols was initiated with the accidental discovery of solanesol in tobacco leaves (Rowland RL et al., J Am Chem Soc 1956, 78, 4680) and isolation of several polyprenols (C30-C45) in cellulose pulp extracts (Lindgren BO, Acta Chem Scan 1965, 19, 1317). As a rule, the chain of these polyisoprenoid alcohols has a number of prenyl units in the range 5 to 25. In general, bacteria, as all prokaryotic cells, possess ditrans-polycis-prenols containing between 10 and 12 units, the most abundant being undecaprenol (trivial name bactoprenol). Yeast cells posess a C16 polyprenol, rat a C18 polyprenol, and human a C19 polyprenol. In mushroom, polyprenols with 17 to 90 isoprenoid units were identified (Ohya N et al, Phytochemistry 1998, 48, 781). In plants, the diversity of polyprenols is much broader, they are tritrans-polycis-prenols and the chain length covers the broad spectrum of compounds ranging from 6 up to 130 carbon atoms (Rezanka T et al., J Chromatogr A 2001, 936, 95). In contrast, mixtures of polyprenols were isolated from old leaves and needles of gymnosperm and angiosperm plants (Ibata K et al., Phytochemistry 1984, 27, 2517). Some of the earliest samples were obtained from Ficus elastica, giving rise to the trivial names ficaprenol-11 and ficaprenol-12 (Stone KJ et al. Biochem J 1967, 102, 325).
Pioneer studies were summarized in a review by Hemming FW (Biochem Cell Biol 1992, 70, 377).
Head-to-tail assembly of the isoprenyl units produces polymers differing not only in chain length but in geometrical configuration.


Some important members of the series are as follows:

n	Number of isoprene unit	Number of carbons	Name
0	2	10	Geraniol
1	3	15	Farnesol
2	4	20	Geranylgeraniol
3	5	25	Geranylfarnesol
7	9	45	Solanesol
8-11	10-13	50-65	Castaprenols-Ficaprenols

They are important molecules in the synthesis of various terpenes, the acylation of proteins and the synthesis of vitamins (Vitamins E and K).  Solanesol, discovered in tobacco leaves in 1956 (Rowland RL et al., J Am Chem Soc 1956, 78, 4680), may be an important precursor of the tumorigenic polynuclear aromatic hydrocarbons of smoke but is also a possible side chain for plastoquinone.
Mono- and sesquiterpenes, which are the partially volatile components of essential oils, can be obtained by steam distillation of the tissues of many plants.

The covalent addition of phosphorylated derivatives of typical isoprenoids, farnesyl pyrophosphate and geranylgeranyl pyrophosphate, to proteins is a process (prenylation) common to G protein subunits. These isoprenylated proteins have key roles in membrane attachment leading to central functionality in cell biology and pathology.

Most eukaryotic cells contain one type of polyisoprenoid alcohols with one a-saturated isoprenoid unit (2,3-dihydro polycis-prenols) which have been called dolichol by Pennock JF et al. (Nature 1960, 186, 470), a derivative of prenols. Most of these carry two trans units at the w-end of the chain.
Dolichols (fro the Greek dolikos: long) have the general structure :

Dolichols isolated from yeast or animal cells consist mainly of seven to eight compounds, those with 16, 18, or 19 isoprenoid units being the most abundant (Ragg SS, Biochem Biophys Res Comm 1998, 243, 1). Dolichol amount was shown to be increased in the brain gray matter of elderly (Pullarkat RK et al., J Biol Chem 1982, 257, 5991). Dolichols with 19, 22 and 23 isoprenoid units were described as early as 1972 in marine invertebrates (Walton MJ et al., Biochem J 1972, 127, 471). Furthermore, the pattern of their distribution may be considered as a chemotaxonomic criterion. It has been reported that a high proportion of dolichols is esterified to fatty acids. As an example, 85-90% of dolichols are esterified in mouse testis (Potter J et al., Biochem Biophys Res Comm 1983, 110, 512). In addition, dlichyl dolichoate has been found in bovine thyroid (Steen L. et al., Biochim Biophys Acta, 1984, 796, 294).
They are well known for their important role as glycosyl carrier in a phosphorylated form in the synthesis of polysaccharides and glycoproteins in yeast cells, and animals. Conversely, they have been identified as the predominant isoprenoid form in roots (Skorupinska-Tudek K et al., Lipids 2003, 38, 981) and in mushroom tissue (Wojtas M et al., Chem Phys Lipids 2004, 130, 109). Similar compounds (ficaprenols) have the same metabolic function in plants. The repartition of the various types of polyisoprenoid alcohols between plants and animals have been extensively discussed (Swiezewska E et al., Prog Lipid Res 2005, 44, 235).

Biosynthesis of polyisoprenoid alcohols and their biological role have been reviewed in 2005 (Swiezewska E et al., Prog Lipid Res 2005, 44, 235).

3 - Phenolic alcohols

Among the simple phenolic alcohols, monolignols are the source materials for biosynthesis of both lignans and lignin. The starting material for production of monolignols (phenylpropanoid) is the amino acid phenylalanine. There are two main monolignols: coniferyl alcohol and sinapyl alcohol. Para-coumaryl alcohol is similar to conipheryl alcohol but without the methoxy group.

Conipheryl alcohol is found in both gymnosperm and angiosperm plants. Sinapyl alcohol and para-coumaryl alcohol, the other two lignin monomers, are found in angiosperm plants and grasses. Conipheryl esters (conypheryl 8-methylnonanoate) have been described in the fruits of the pepper, Capsicum baccatum (Kobata K et al., Phytochemistry 2008, 69, 1179). These compounds displayed an agonist activity for transient receptor potential vanilloid 1 (capsaicin receptor) as the well known capsaicinoids present in these plant species.

Complex phenolic alcohols (phenolphthiocerol) were shown to be components of Mycobacterium glycolipids which are termed glycosides of phenolphthiocerol dimycocerosate (Smith DW et al., Nature 1960, 186, 887) belonging to the large family of "mycosides". The chain length differs according to the homologues, 18 and 20 carbon atoms in  mycosides A, and B, respectively. One of these phenolphthiocerols is shown below.

An analogue component but with a ketone group instead of the methoxy group, a phenolphthiodiolone, has been detected in mycoside A (Fournie JJ et al., J Biol Chem 1987, 262, 3174).

FATTY ALDEHYDES

Long-chain aldehydes are found in free form, but also in the form of vinyl ether (known as alk-1-enyl ether) integated in glycerides and phospholipids (plasmalogens).
The free aldehydes can be as fatty acids saturated or unsaturated. They have a general formula CH₃(CH₂)_nCHO with n=6 to 20 or greater. The most common is palmitaldehyde (hexadecanal) with a 16 carbon chain. Normal monoenoic aldehydes are analogous to the monoenoic fatty acids.
It must be noticed that an aldehyde function may be found at a terminal (w) position while an acid function is present at the other end of the carbon chain (oxo fatty acids). These compounds have important signaling properties in plants.
Long-chain aldehydes have been described in the waxes which impregnate the matrix covering all organs of plants (Vermeer CP et al., Phytochemistry 2003, 62, 433). These compounds forming about 7% of the leaf cuticular waxes of Ricinus communis were identified as homologous unbranched aldehydes ranging from C22 to C28 with a hydroxyl group at the carbon 3. Long-chain 5-hydroxyaldehydes with chain lengths from C24 to C36, the C28 chain being the most abundant, were identified in the cuticular wax of Taxux baccata needles (Wen M et al., Phytochemistry 2007, 68, 2563).   


Aldehydes may be produced during decomposition of fatty acid hydroperoxides following a peroxidation attack. Several aldehydes (hexanal, heptanal..) belong to aroma compounds which are found in environmental or food systems (see the website: Flavornet). 
Fatty aldehydes may be determined easily by TLC or gas liquid chromatography (follow that link). The most common method for the determination of aldehydes involves derivatization with an acidic solution of 2,4-dinitrophenylhydrazine to form corresponding hydrazones followed by HPLC separation and UV–VIS detection. An optimized derivatization procedure for the determination of aliphatic C1-C10 aldehydes has been described (Stafiej A et al., J Biochem Biophys Meth 2006, 69, 15).
Other short-chain aldehydes (octadienal, octatrienal, heptadienal) are produced via a lipoxygenase-mediated pathway from polyunsaturated fatty acids esterifying glycolipids in marine diatoms (D'Ippolito G et al., Biochim Biophys Acta 2004, 1686, 100). Several short-chain aldehydes were shown to induce deleterious effects on zooplankton crustaceans and thus limiting the water secondary production (birth-control aldehydes) (D'Ippolito G et al., Tetrahedron Lett 2002, 43, 6133). In laboratory experiments, three decatrienal isomers produced by various diatoms were shown to arrest embryonic development in copepod and sea urchins and have antiproliferative and apoptotic effects on carcinoma cells (Miralto A et al., Nature 1999, 402, 173). Later, the copepod recruitment in blooms of planktonic diatom was shown to be suppressed by ingestion of dinoflagellate aldehydes (Nature 2004, 429, 403).

Long after the demonstration of the presence of iodinated lipids in thyroid (besides iodinated aminoacids), it was shown that the major iodinated lipid formed in thyroid when incubated in vitro with iodide was 2-iodohexadecanal (Pereira A et al, J Biol Chem 1990, 265, 17018). In rat and dog thyroid, 2-iodooctadecanal was determined to be more abundant that the 16-carbon aldehyde. These compounds, which are thought to play a role in the regulation of thyroid function, were recently shown to be formed by the attack of reactive iodine on the vinyl ether group of PE plasmalogen. This attack generates an unstable iodinated derivative which breaks into lysophosphatidylethanolamine and 2-iodo aldehydes (Panneels V et al, J Biol Chem 1996, 271, 23006).

In some bacteria, aldehyde analogs of cyclopropane fatty acids were described.

Several fatty aldehydes are known to have pheromone functions. Studies in African and Asian countries have shown that the use of 10,12-hexadecadienal could be effective for control of the spiny bollworm Earias insulana, a cotton pest. The sex pheromone of the navel orange worm, Amyelois transitella, 11,13-hexadecadienal, is usually used in the control of this citric pest.

Several isoprenoid aldehydes are important in insect biology as pheromones and in botany as volatile odorous substances. Some examples are given below:

Retinal exist in two forms, a cis and a trans isomer. On illumination with white light, the visual pigment, rhodopsin is converted to a mixture of a protein (opsin) and trans-retinal. This isomer must be transformed into the cis form by retinal isomerase before it combines again with opsin (dark phase). Both isomers can be reduced to retinol (vitamin A) by a NADH dependent alcohol dehydrogenase. Retinol is stocked in retina mainly in an acylated form.