Cyclic compound

A cyclic compound (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 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 valences 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. Ingenol, a complex, terpenoid natural product, related to but simpler than the paclitaxel that follows, which displays a complex ring structure including 3-, 5-, and 7-membered non-aromatic, carbocyclic rings.Cycloalkanes, the simplest carbocycles, including cyclopropane, cyclobutane, cyclopentane, and cyclohexane. Note, elsewhere an organic chemistry shorthand is used where hydrogen atoms are inferred as present to fill the carbon's valence of 4 (rather than their being shown explicitly).Paclitaxel, another complex, plant-derived terpenoid, also a natural product, displaying a complex multi-ring structure including 4-, 6-, and 8-membered rings (carbocyclic and heterocyclic, aromatic and non-aromatic).Cycloheptane, a simple 7-membered carbocyclic compound, methylene hydrogens shown (non-aromatic).Benzene, a 6-membered carbocyclic compound. methine hydrogens shown, and 6 electrons shown as delocalized through drawing of circle (aromatic).Cyclo-octasulfur, an 8-membered inorganic cyclic compound (non-aromatic).Pentazole, a 5-membered inorganic cyclic compound (aromatic).Azetidine, a 4-membered nitrogen (aza) hetero-cyclic compound, methylene hydrogen atoms implied, not shown (non-aromatic).Pyridine, a 6 membered heterocyclic compound, methine hydrogen atoms implied, not shown, and delocalized π-electrons shown as discrete bonds (aromatic).Naphthalene, technically a polycyclic, more specifically a bicyclic compound, with circles showing delocalization of π-electrons (aromatic).Decalin (decahydronaphthalene), the fully saturated derivative of naphthalene, showing the two stereochemistries possible for 'fusing' the two rings together, and how this impacts the shapes available to this bicyclic compound (non-aromatic).Longifolene, a terpene natural product, and an example of a tricyclic molecule (non-aromatic).Paclitaxel, a polycyclic natural product 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-rings on its 'tail', and attached to C-2 (abbrev. Ph, C6H5; aromatics).A representative three-dimensional shape adopted by paclitaxel, as a result of its unique cyclic structure.Cholesterol, another terpene natural product, in particular, a steroid, a class of tetracyclic molecules (non-aromatic).Benzopyrene, a pentacyclic compound both natural and man-made, and delocalized π-electrons shown as discrete bonds (aromatic).Pagodane, a complex, highly symmetric, man-made polycyclic compound (non-aromatic).Brevetoxin A, a natural product with ten rings, all fused, and all heterocyclic, and a toxic component associated with the organisms responsible for red tides. The R group at right refers to one of several possible four-carbon side chains (see main Brevetoxin article; non-aromatic). A cyclic compound (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 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 valences 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. Adding to their complexity and number, closing of atoms into rings may lock particular atoms with distinct substitution (by functional groups) such that stereochemistry 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 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. Finally, cyclic compounds, because of the unique shapes, reactivities, properties, and bioactivities that they engender, are the largest majority of all molecules involved in the biochemistry, structure, and function of living organisms, and in the man-made molecules (e.g., drugs, herbicides, etc.). A cyclic compound or ring compound is a compound at least some of whose atoms are connected to form a ring.:unknown Rings vary in size from 3 to many tens or even hundreds of atoms. Examples of ring compounds readily include cases where: Common atoms can (as a result of their valences) 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 aromatic 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 functional group–substituted atoms into place, resulting in stereochemistry 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 5-atoms and larger—can vary and interconvert such that conformational isomerism is displayed. IUPAC 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 8 or more atoms. The term polycyclic is used when more than one ring appears in a single molecule. Naphthalene 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. 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 atoms form cyclic compounds as well. Examples include sulfur, silicon (e.g., in silanes), phosphorus (e.g., in phosphanes and phosphoric acid variants), and boron (e.g., in triboric acid). When carbon in benzene is 'replaced' by other elements, e.g., as in borabenzene, silabenzene, germanabenzene, stannabenzene, and phosphorine, aromaticity is retained, and so aromatic inorganic cyclic compounds are known and well-characterized.