HOME

TheInfoList

Click Here for Items Related To - Cyclization Reaction

OR:

Cyclization Reaction on: [Wikipedia] [Google] [Amazon]

A cyclic compound (or ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where all the atoms are carbon (i.e., are carbocycles), none of the atoms are carbon (inorganic cyclic compounds), or where both carbon and non-carbon atoms are present ( heterocyclic compounds). Depending on the ring size, the bond order of the individual links between ring atoms, and their arrangements within the rings, carbocyclic and heterocyclic compounds may be

aromatic In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to sat ...

or non-aromatic; in the latter case, they may vary from being fully saturated to having varying numbers of multiple bonds between the ring atoms. Because of the tremendous diversity allowed, in combination, by the

valence Valence or valency may refer to: Science * Valence (chemistry), a measure of an element's combining power with other atoms * Degree (graph theory), also called the valency of a vertex in graph theory * Valency (linguistics), aspect of verbs rel ...

s of common atoms and their ability to form rings, the number of possible cyclic structures, even of small size (e.g., < 17 total atoms) numbers in the many billions. natural Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...

cyclic compounds" widths="250 px" align="center"> Image: Ingenol.svg,

Ingenol Ingenol mebutate, sold under the brand name Picato, is a substance that is found in the sap of the plant ''Euphorbia peplus'', commonly known as milkweed, and is an inducer of cell death. A gel formulation of the drug has been approved by the U.S. ...

, a complex,

terpenoid The terpenoids, also known as isoprenoids, are a class of naturally occurring organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeably with "terpenes ...

natural product A natural product is a natural compound or substance produced by a living organism—that is, found in nature. In the broadest sense, natural products include any substance produced by life. Natural products can also be prepared by chemical sy ...

, related to but simpler than the

paclitaxel Paclitaxel (PTX), sold under the brand name Taxol among others, is a chemotherapy medication used to treat a number of types of cancer. This includes ovarian cancer, esophageal cancer, breast cancer, lung cancer, Kaposi's sarcoma, cervical can ...

that follows, which displays a complex ring structure including 3-, 5-, and 7-membered non-

, carbocyclic rings. Image:First four cycloalkanes - en.svg ,

Cycloalkane In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containin ...

s, the simplest carbocycles, including cyclopropane,

cyclobutane Cyclobutane is a cycloalkane and organic compound with the formula (CH2)4. Cyclobutane is a colourless gas and commercially available as a liquefied gas. Derivatives of cyclobutane are called cyclobutanes. Cyclobutane itself is of no commercia ...

cyclopentane Cyclopentane (also called C pentane) is a highly flammable alicyclic hydrocarbon with chemical formula C5H10 and CAS number 287-92-3, consisting of a ring of five carbon atoms each bonded with two hydrogen atoms above and below the plane. It oc ...

, and

cyclohexane Cyclohexane is a cycloalkane with the molecular formula . Cyclohexane is non-polar. Cyclohexane is a colorless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products (in which it is sometimes used). Cyclohex ...

. Note, elsewhere an

organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...

shorthand is used where hydrogen atoms are inferred as present to fill the carbon's valence of 4 (rather than their being shown explicitly). Image:Taxol.svg ,

Paclitaxel Paclitaxel (PTX), sold under the brand name Taxol among others, is a chemotherapy medication used to treat a number of types of cancer. This includes ovarian cancer, esophageal cancer, breast cancer, lung cancer, Kaposi's sarcoma, cervical can ...

, another complex, plant-derived

, also a natural product, displaying a complex multi-ring structure including 4-, 6-, and 8-membered rings (carbocyclic and heterocyclic,

and non-aromatic). Adding to their complexity and number, closing of atoms into rings may lock particular atoms with distinct substitution (by

functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the res ...

s) such that

stereochemistry Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereo ...

and chirality of the compound results, including some manifestations that are unique to rings (e.g., configurational isomers). As well, depending on ring size, the three-dimensional shapes of particular cyclic structures – typically rings of five atoms and larger – can vary and interconvert such that conformational isomerism is displayed. Indeed, the development of this important chemical concept arose historically in reference to cyclic compounds. Finally, cyclic compounds, because of the unique shapes, reactivities, properties, and bioactivities that they engender, are the majority of all molecules involved in the biochemistry, structure, and function of

living organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

s, and in man-made molecules such as drugs, pesticides, etc.

Structure and classification

A cyclic compound or ring compound is a compound in which at least some its atoms are connected to form a ring. Rings vary in size from three to many tens or even hundreds of atoms. Examples of ring compounds readily include cases where: * all the atoms are carbon (i.e., are carbocycles), * none of the atoms are carbon (inorganic cyclic compounds), or where * both carbon and non-carbon atoms are present ( heterocyclic compounds). Common atoms can (as a result of their

s) form varying numbers of bonds, and many common atoms readily form rings. In addition, depending on the ring size, the bond order of the individual links between ring atoms, and their arrangements within the rings, cyclic compounds may be

or non-aromatic; in the case of non-aromatic cyclic compounds, they may vary from being fully saturated to having varying numbers of multiple bonds. As a consequence of the constitutional variability that is thermodynamically possible in cyclic structures, the number of possible cyclic structures, even of small size (e.g., <17 atoms) numbers in the many billions. Moreover, the closing of atoms into rings may lock particular

–

substituted A substitution reaction (also known as single displacement reaction or single substitution reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions ar ...

atoms into place, resulting in

and chirality being associated with the compound, including some manifestations that are unique to rings (e.g., configurational isomers); As well, depending on ring size, the three-dimensional shapes of particular cyclic structures — typically rings of five atoms and larger — can vary and interconvert such that conformational isomerism is displayed.

Carbocycles

The vast majority of cyclic compounds are organic, and of these, a significant and conceptually important portion are composed of rings made only of carbon atoms (i.e., they are carbocycles).

Inorganic cyclic compounds

Inorganic atoms form cyclic compounds as well. Examples include

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

(e.g. in

polysulfide Polysulfides are a class of chemical compounds containing chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. Among the inorganic polysulfides, there are ones which contain anions, which have the general formu ...

s),

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

(e.g., in silanes),

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...

(e.g., in phosphanes, metaphosphates and other

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solutio ...

derivatives), and boron (e.g., in triboric acid). When carbon in benzene is "replaced" by other elements, e.g., as in borabenzene, silabenzene,

germanabenzene Germabenzene (C5H6Ge) is the parent representative of a group of chemical compounds containing in their molecular structure a benzene ring with a carbon atom replaced by a germanium atom. Germabenzene itself has been studied theoretically, and syn ...

stannabenzene Stannabenzene (C5H6Sn) is the parent representative of a group of organotin compounds that are related to benzene with a carbon atom replaced by a tin atom. Stannabenzene itself has been studied by computational chemistry, but has not been isolate ...

, and

phosphorine Phosphorine ( IUPAC name: phosphinine) is a heavier element analog of pyridine, containing a phosphorus atom instead of an aza- moiety. It is also called phosphabenzene and belongs to the phosphaalkene class. It is a colorless liquid that is ...

, aromaticity is retained, and so aromatic inorganic cyclic compounds are also known and well-characterized.

Heterocyclic compounds

Cyclic compounds that have both carbon and non-carbon atoms present are termed

heterocyclic compounds A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...

; alternatively the name can refer to inorganic cyclic compounds, such as siloxanes and borazines, that have more than one type of atom in their rings. Hantzsch–Widman nomenclature is recommended by the IUPAC for naming heterocycles, but many common names remain in regular use.

Macrocycles

The term macrocycle is used for compounds having a rings of 8 or more atoms. Macrocycles may be fully carbocyclic, heterocyclic but having limited heteroatoms (e.g., in

lactone Lactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by intramolecular esterification of the co ...

s and lactams), or be rich in heteroatoms and displaying significant symmetry (e.g., in the case of chelating macrocycles). Macrocycles can access a number of stable conformations, with preference to reside in conformations that minimize transannular nonbonded interactions within the ring (e.g., with the chair and chair-boat being more stable than the boat-boat conformation for cyclooctane, because of the interactions depicted by the arcs shown). Medium rings (8-11 atoms) are the most strained, with between 9-13 (kcal/mol) strain energy, and analysis of factors important in the conformations of larger macrocycles can be modeled using medium ring conformations. Conformational analysis of odd-membered rings suggests they tend to reside in less symmetrical forms with smaller energy differences between stable conformations. Macrocycles 2revEnglUse

Nomenclature

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

nomenclature has extensive rules to cover the naming of cyclic structures, both as core structures, and as substituents appended to alicyclic structures. The term macrocycle is used when a ring-containing compound has a ring of 12 or more atoms. The term polycyclic is used when more than one ring appears in a single molecule.

Naphthalene Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromat ...

is formally a polycyclic compound, but is more specifically named as a bicyclic compound. Several examples of macrocyclic and polycyclic structures are given in the final gallery below. The atoms that are part of the ring structure are called annular atoms.

Isomerism

Stereochemistry

The closing of atoms into rings may lock particular atoms with distinct substitution by functional groups such that the result is

and chirality of the compound, including some manifestations that are unique to rings (e.g., configurational isomers).

Conformational isomerism

Depending on ring size, the three-dimensional shapes of particular cyclic structures—typically rings of 5-atoms and larger—can vary and interconvert such that conformational isomerism is displayed. Indeed, the development of this important chemical concept arose, historically, in reference to cyclic compounds. For instance,

s—six membered carbocycles with no double bonds, to which various substituents might be attached, see image—display an equilibrium between two conformations, the ''chair'' and the ''boat,'' as shown in the image. The chair conformation is the favored configuration, because in this conformation, the steric strain, eclipsing strain, and angle strain that are otherwise possible are minimized. Which of the ''possible'' chair conformations predominate in cyclohexanes bearing one or more substituents depends on the substituents, and where they are located on the ring; generally, "bulky" substituents—those groups with large '' volumes,'' or groups that are otherwise repulsive in their interactions—prefer to occupy an equatorial location. An example of interactions within a molecule that would lead to steric strain, leading to a shift in equilibrium from boat to chair, is the interaction between the two

methyl group In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in ma ...

s in ''cis''-1,4-dimethylcyclohexane. In this molecule, the two methyl groups are in opposing positions of the ring (1,4-), and their ''cis'' stereochemistry projects both of these groups toward the same side of the ring. Hence, if forced into the higher energy boat form, these methyl groups are in steric contact, repel one another, and drive the equilibrium toward the chair conformation.

Aromaticity

Cyclic compounds may or may not exhibit

aromaticity In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to sat ...

;

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen ato ...

is an example of an aromatic cyclic compound, while

is non-aromatic. In organic chemistry, the term aromaticity is used to describe a cyclic (ring-shaped), planar (flat) molecule that exhibits unusual stability as compared to other geometric or connective arrangements of the same set of atoms. As a result of their stability, it is very difficult to cause aromatic molecules to break apart and to react with other substances. Organic compounds that are not aromatic are classified as aliphatic compounds—they might be cyclic, but only aromatic rings have especial stability (low reactivity). Since one of the most commonly encountered aromatic systems of compounds in organic chemistry is based on derivatives of the prototypical aromatic compound benzene (an aromatic hydrocarbon common in petroleum and its distillates), the word “aromatic” is occasionally used to refer informally to benzene derivatives, and this is how it was first defined. Nevertheless, many non-benzene aromatic compounds exist. In living organisms, for example, the most common aromatic rings are the double-ringed bases in RNA and DNA. A functional group or other substituent that is aromatic is called an aryl group. The earliest use of the term “aromatic” was in an article by August Wilhelm Hofmann in 1855. Hofmann used the term for a class of benzene compounds, many of which do have odors (aromas), unlike pure saturated hydrocarbons. Today, there is no general relationship between aromaticity as a chemical property and the olfactory properties of such compounds (how they smell), although in 1855, before the structure of benzene or organic compounds was understood, chemists like Hofmann were beginning to understand that odiferous molecules from plants, such as terpenes, had chemical properties we recognize today are similar to unsaturated petroleum hydrocarbons like benzene. In terms of the electronic nature of the molecule, aromaticity describes a conjugated system often made of alternating single and double bonds in a ring. This configuration allows for the electrons in the molecule’s pi system to be delocalized around the ring, increasing the molecule's stability. The molecule cannot be represented by one structure, but rather a resonance hybrid of different structures, such as with the two resonance structures of benzene. These molecules cannot be found in either one of these representations, with the longer single bonds in one location and the shorter double bond in another (See Theory below). Rather, the molecule exhibits bond lengths in between those of single and double bonds. This commonly seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds (cyclohexatriene), was developed by August Kekulé (see History section below). The model for benzene consists of two resonance forms, which corresponds to the double and single bonds superimposing to produce six one-and-a-half bonds. Benzene is a more stable molecule than would be expected without accounting for charge delocalization.

Principal uses

Because of the unique shapes, reactivities, properties, and bioactivities that they engender, cyclic compounds are the largest majority of all molecules involved in the biochemistry, structure, and function of

s, and in the man-made molecules (e.g., drugs, herbicides, etc.) through which man attempts to exert control over nature and biological systems.

Synthetic reactions

Important general reactions for forming rings

There are a variety of specialized reactions whose use is solely the formation of rings, and these will be discussed below. In addition to those, there are a wide variety of ''general'' organic reactions that historically have been crucial in the development, first, of understanding the concepts of ring chemistry, and second, of reliable procedures for preparing ring structures in high yield, and with defined orientation of ring substituents (i.e., defined

). These general reactions include: * Acyloin condensation; * Anodic oxidations; and * the Dieckmann condensation as applied to ring formation.

Ring-closing reactions

In organic chemistry, a variety of synthetic procures are particularly useful in closing carbocyclic and other rings; these are termed ''ring-closing reactions''. Examples include: *

alkyne trimerisation In organic chemistry, an alkyne trimerisation is a +2+2nbsp; cycloaddition reaction in which three alkyne units () react to form a benzene ring. The reaction requires a metal catalyst. The process is of historic interest as well as being appl ...

; * the

Bergman cyclization The Masamune-Bergman cyclization or Masamune-Bergman reaction or Masamune-Bergman cycloaromatization is an organic reaction and more specifically a rearrangement reaction taking place when an enediyne is heated in presence of a suitable hydrogen ...

of an enediyne; * the Diels–Alder, between a conjugated diene and a substituted

alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...

, and other cycloaddition reactions; * the Nazarov cyclization reaction, originally being the cyclization of a divinyl ketone; * various radical cyclizations; * ring-closing metathesis reactions, which also can be used to accomplish a specific type of

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

; * the Ruzicka large ring synthesis, in which two

carboxyl In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyl ...

groups combine to form a

carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containin ...

group with loss of and ; * the Wenker synthesis converting a beta

amino alcohol In organic chemistry, alkanolamines are organic compounds that contain both hydroxyl () and amino (, , and ) functional groups on an alkane backbone. The term alkanolamine is a broad class term that is sometimes used as a subclassification. Meth ...

to an aziridine * other reactions, such as an

amino group In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...

reacting with a

hydroxy group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...

, as in the biosynthesis of solanine

Ring-opening reactions

A variety of further synthetic procedures are particularly useful in opening carbocyclic and other rings, generally which contain a double bound or other

"handle" to facilitate chemistry; these are termed ''ring-opening reactions''. Examples include: * ring opening metathesis, which can also be used to accomplish a specific type of

Ring expansion and ring contraction reactions

Ring expansion and contraction reactions are common in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

, and are frequently encountered in pericyclic reactions. Ring expansions and contractions can involve the insertion of a functional group such as the case with Baeyer–Villiger oxidation of cyclic ketones, rearrangements of cyclic carbocycles as seen in intramolecular Diels-Alder reactions, or collapse or rearrangement of

bicyclic compound In chemistry, a bicyclic molecule () is a molecule that features two joined rings. Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and camphor. A bicyclic compound can be carbocyclic (all o ...

s as several examples.

Examples

Simple, mono-cyclic examples

The following are examples of simple and aromatic carbocycles, inorganic cyclic compounds, and heterocycles: Image:Cycloheptane.png ,

Cycloheptane Cycloheptane is a cycloalkane with the molecular formula C7 H14. Cycloheptane is used as a nonpolar solvent for the chemical industry and as an intermediate in the manufacture of chemicals and pharmaceutical drugs. It may be derived by Clemmens ...

, a simple 7-membered carbocyclic compound, methylene hydrogens shown (non-aromatic). Image:Benz4.png ,

Benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen ato ...

, a 6-membered carbocyclic compound. methine hydrogens shown, and 6 electrons shown as delocalized through drawing of circle (aromatic). Image:Cyclooctasulfur_structural_formula_3D.svg , ''Cyclo''- octasulfur, an 8-membered inorganic cyclic compound (non-aromatic). Image:Pentazole.svg , Pentazole, a 5-membered inorganic cyclic compound (aromatic). Image:Azetidine structure.svg, Azetidine, a 4-membered

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...

(aza) hetero-cyclic compound, methylene hydrogen atoms implied, not shown (non-aromatic). Image:Pyridine.svg,

Pyridine Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakl ...

, a 6 membered heterocyclic compound, methine hydrogen atoms implied, not shown, and delocalized π-electrons shown as discrete bonds (aromatic).

Complex and polycyclic examples

The following are examples of cyclic compounds exhibiting more complex ring systems and stereochemical features: Image:Naphtalene topo.svg ,

, technically a polycyclic, more specifically a bicyclic compound, with circles showing delocalization of π-electrons (aromatic). Image:Cis-trans isomerism of decahydronaphthalene.svg , Decalin (decahydronaphthalene), the fully saturated derivative of

naphthalene Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromat ...

, showing the two stereochemistries possible for "fusing" the two rings together, and how this impacts the shapes available to this bicyclic compound (non-aromatic). Image:Longifolene plus acsv.svg,

Longifolene Longifolene is the common (or trivial) chemical name of a naturally occurring, oily liquid hydrocarbon found primarily in the high-boiling fraction of certain pine resins. The name is derived from that of a pine species from which the compound ...

, a

terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n > 1. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes ar ...

, and an example of a tricyclic molecule (non-aromatic). Image:TaxolNumberingScheme.svg ,

, a polycyclic

with a tricyclic core: with a heterocyclic, 4-membered D ring, fused to further 6- and 8-membered carbocyclic (A/C and B) rings (non-aromatic), and with three further pendant

phenyl In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydroge ...

-rings on its "tail", and attached to C-2 (abbrev. Ph, C₆H₅; aromatics). Image:Paclitaxel_JMolBiol_2001_1045.jpg , A representative three-dimensional shape adopted by

, as a result of its unique cyclic structure. Image:Cholesterol.svg,

Cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell membr ...

, another terpene natural product, in particular, a

steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and ...

, a class of tetracyclic molecules (non-aromatic). Image:Benzo-a-pyrene.svg, Benzo yrene, a pentacyclic compound both natural and man-made, and delocalized π-electrons shown as discrete bonds (aromatic). Image:Pagodane.svg, Pagodane, a complex, highly symmetric, man-made polycyclic compound (non-aromatic). Image:Brevetoxin A.svg, Brevetoxin A, a

with ten rings, all fused, and all heterocyclic, and a toxic component associated with the organisms responsible for

red tide A harmful algal bloom (HAB) (or excessive algae growth) is an algal bloom that causes negative impacts to other organisms by production of natural phycotoxin, algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are ...

s. The R group at right refers to one of several possible four-carbon side chains (see main Brevetoxin article; non-aromatic).

References

External links

* * {{Authority control Cyclic compounds, Molecular geometry