Hydrocarbons fused ring systems

Polycyclic aliphatic hydrocarbons. These may contain two or more rings that share two or more carbon atoms. An example of a fused-ring system is... 

In fused ring systems, the positions are not equivalent and there is usually a preferred orientation even in the unsubstituted hydrocarbon. The preferred positions may often by predicted as for benzene rings. Thus it is possible to draw more canonical forms for the arenium ion when naphthalene is attacked at the a position than when it is attacked at the p position, and the a position is the preferred site of attack,though, as previously mentioned (p. 682), the isomer formed by substitution at the p position is thermodynamically more stable and is the product if the reaction is reversible and equilibrium is reached. Because of the more extensive delocalization of charges in the corresponding arenium ions, naphthalene is more reactive than benzene and substitution is faster at both positions. Similarly, anthracene, phenanthrene, and other fused polycyclic aromatic hydrocarbons are also substituted faster than benzene. 

Analytical Properties Separation of lower aromatic hydrocarbons and small fused-ring systems using toluene and hexane methanol as the stationary phases the relatively low pressure rating on the polymeric phase limits solvent flow rate Reference 11-13... 

Fused ring systems that have other bridges are usually named by prefixing the name of the bridge to the name of the fused ring system. The names of hydrocarbon bridges are derived from the names of the parent hydrocarbons by replacing the final -ane, -ene, etc., by -ano, -eno, etc. Thus, -CH2- is methano and -CH=CH- is etheno. 

Polycyclic aromatic hydrocarbons 3.612a,b and 3.613a, containing 9- and 11-fused ring systems, respectively, were synthesized by a similar method to that used for the enediyne lithium derivative 3.545. It involved the condensation of appropriate tetraacetylenic derivatives 3.608-3.610... 

Organic compounds that contain benzene rings as part of their molecular structure are called aromatic compounds. Nonaromatic hydrocarbons such as alkanes, alkenes, and alkynes are called aliphatic compounds. Some aromatic compounds contain two or more benzene rings fused together. Examples include naphthalene and anthracene. In these compounds, electrons are shared over all of the carbon atoms in the fused ring system. 

Stelzner Method. This is a general method of applying replacement nomenclature to ring systems it differs from the Chemical Abstracts procedure in that replacement principles are applied in all cases to the name of the hydrocarbon with the same bond distribution in the rings as the heterocycle to be named. This leads to no difference for monocycles (see examples 1-3), but in the case of fused skeletons the parent hydrocarbon of a fully unsaturated heterocycle is frequently a partially hydrogenated molecule. The parent hydrocarbon name for application of either replacement method can be trivial or a name derived by fusion principles (as above). The examples 21-24 of both... 

Alternate to part of Rule A-23.1)—The names of ort/io-fused polycyclic hydrocarbons which have (a) less than the maximum number of non-cumulative double bonds, (b) at least one terminal unit which is most conveniently named as an unsaturated cycloalkane derivative, and (c) a double bond at the positions where rings are fused together, may be derived by joining the name of the terminal unit to that of the other component by means of a letter o with elision of a terminal e . The abbreviations for fused aromatic systems laid down in Rule A-21.4 are used, and the exceptions of Rule A-23.1 apply. 

Bivalent radicals derived from o/7/io-fused or ortho- and pen-fused polycyclic hydrocarbons by removal of a hydrogen atom from each of two different carbon atoms of the ring are named by changing the ending -yl of the univalent radical name to -ylene or -diyl . Multivalent radicals, similarly derived, are named by adding -triyl , -tetrayl , etc., to the name of the ring system. 

Orf/io-fused and ortho- and pen-fused ring compounds containing hetero atoms are named according to the fusion principle described in Rule A-21 for hydrocarbons. The components are named according to Rules A-21, B-l and B-2. When the name of a component in a fusion name contains locants (numerals or letters) that do not apply also to the numbering of the fused system, these locants are placed in square brackets (as are also the locants for fusion positions required by Rule A-21.5). The base component should be a heterocyclic system. If there is a choice, the base component should be, by order of preference ... 

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