Polycyclic compound

Polycyclic compounds or short polycycles (singular Polycyclus ) are cyclic organic chemical compounds are those in which atoms arranged in multiple rings. If the compounds contain only one ring, one speaks instead of monocycles. With very few exceptions, only carbon is able to form stable polycyclic compounds. Within the ring system are heteroatoms such as nitrogen, oxygen, sulfur or phosphorus are present, is called the polycyclic heterocyclic compounds. If two or more rings directly linked by single compounds, then one speaks of ring sequences.

Polycyclic compounds are very common in nature. For example, include the steroids to the polycyclic compounds.

Nomenclature

Many polycyclic wear trivial names, but they are " allowed" also according to IUPAC nomenclature. The systematic nomenclature of polycyclic compounds is sometimes complicated and depends on the number of rings, the total number of ring carbon atoms ( parent hydrocarbon ), the number of atoms between the bridgehead carbon atoms and the way down, after which linked the rings are.

• For polycyclic compounds that consist of two rings, the name or bicyclic bicyclic compound is common, such as: naphthalene. With three rings is called tricyclic compounds.
• Two directly adjacent rings with a common bond are also referred to as fused or fused ring system (examples: naphthalene, anthracene, phenanthrene, pyrene ).

Distinguish the type of bonding of the Rings

• Spiro compounds are polycyclic compounds in which rings are connected through a single common atom. They are called spiro- in chemical nomenclature, the prefix.
• Ring associations are ring systems that are Linked together by single or double bonds. Example: biphenyl
• Condensed polycyclic compounds are polycyclic compounds, in which the rings ( a common bond that is exactly ) are each connected by exactly two atoms in common. Examples: naphthalene, anthracene, and phenanthrene. Aromatic condensed polycyclic be treated under the heading of Polycyclic Aromatic Hydrocarbons ( PAHs). Fused systems, which are also referred to as a bridge having bridged condensed polycyclic systems.
• Bridged polycyclic compounds themselves are polycyclic, in which the rings are linked by two or more atoms in common. They are often referred to in the chemical nomenclature for the von Baeyer system. Examples are the bicyclic terpenes bornane ( camphane ), Caran, camphor, Fenchan, fenchone, Pinan, the pinene, and thujone.

Distinction for missing or double bonds present

Many polycyclic compounds can be formally attributed to an aromatic carbocyclic or heterocyclic base structure, which contains the maximum according to the valence number of double bonds. If you mentally hydrogen atoms added to these double bonds, in other words, the double bonds " saturates ", one comes to "Hydro- derivatives ". In practice this is often achieved by (catalytic ) hydrogenation, but in principle makes the experiment for the nomenclature of no importance.

A typical example are the hydrogenated naphthalenes, as the decalins. After Von Baeyer nomenclature they are referred to as bicyclo [ 4.4.0 ] decane. The compounds were, however, obtained by hydrogenation of naphthalene. Without destruction of the ring skeleton maximum of ten H atoms may be attached, hence the hydrocarbon Decahydronapthalin was called. Complete hydrogenation is in the nomenclature also expressed by the prefix " Perhydro ". Formal and often in reality are partially ( " partial" ) hydrogenation of hydrocarbons having the maximum number of double bonds possible. This " partially hydrogenated " compounds are represented by the prefixes " dihydro ", " tetrahydro " - " hexahydro " so characterized, and more. The position of the "Hydro- hydrogen atoms" is indicated by the numbering, the locants the maximum unsaturated ring systems; so rates may be different isomers.

Hydronaphthaline: decahydronaphthaline ( decalin ), 1,2,3,4- tetrahydronaphthalene ( tetralin ), 1,2- dihydronaphthalene, 9,10- dihydronaphthalene. The hydrogen atoms are not shown. Wherein the first and last Hydronaphthalin are stereoisomers (cis and trans ) is possible.

From the structural formulas mono-or bicyclic hydrocarbons of two carbon atoms or inserting carbon chains ( "bridges" ) be able to link the formulas of bridged polycyclic hydrocarbons are derived ( see Article Bridged hydrocarbons). A selection is given in the table.