What is the mirror plane of naphthalene

Molecules with Dnh-Symmetry

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The symmetries D.nh are extremely common and aesthetically very appealing. We consider some typical situations in turn.

The point group D2h
The D.2h-Symmetry has a special position because here the main axis does not differ from the secondary axes by a count> 2. The important examples include ethene and the oxalate ion. Among the condensed aromatics, quite a few have D.2h-Symmetry. These include the particularly important ones, namely naphthalene C.10H8 (Left picture, left molecule) and anthracene C14H10 (Fig. Left, molecule right), while phenanthrene, which is more stable than anthracene and which is more stable (Fig. Right), has less symmetry.

Star molecules
Star molecules have single-bonded, i.e. radially oriented groups around a central atom. The most important examples are boron trifluoride BF3 and xenon tetrafluoride XeF4, the carbonate ion CO32- and the nitrate ion NO3-. This type also includes the square-planar d8-Complexes ML4where L is a halogen or the cyano ligand, such as [Ni (CN)4]2-, [PtCl4]2- and [AuCl4]-.

Bipyramidal Molecules
The original example of bipyramidal molecules is the phosphorus pentafluoride PF5. This subheading also includes iodine heptafluoride IF7 and the pentacarbonyl iron Fe (CO)5 (Honey yellow liquid, bp. 102 ° C, chemically robust, cheap, also noteworthy as a volatile iron compound). Closely related is the structure type of those species that have the same fragment of on both sides of a mirror plane C.nv-Possess symmetry. Many metal ions form complexes of the type [X3M (µ-X)3MX3] such as [Cr2Cl9]3- with two face-linked octahedra. In the chemistry of metal carbonyls, Fe2(CO)9 an amazingly similar structure.

Polygonal molecules
The Hückel hydrocarbon species C are a fundamentally important class3H3+, C4H42-, C5H5-, C6H6, C7H7+ and C8H82-. These polygonal species have one D.nh-Symmetry. They are comparatively unusually stable, which is related to the presence of a "magic" number of 2, 6 or 10 π-electrons. Among these species is the archetype of an aromatic compound, benzene C6H6. [Note: The chemistry of the cyclopropenium ions and the cyclobutadiene anions is subject to very restrictive conditions, which we will not go into in this context.]

Sandwich molecules
D.nh-Symmetry also have the ferrocene Fe (C5H5)2 (orange-colored crystals, m.p. 173 ° C thermal decomposition> 500 ° C, discovered 1951/52), the analogous bis (benzene) chromium Cr (C6H6)2 (greenish black crystals, very sensitive to air, a complex of chromium (0)) and the uranocene U (C8H8)2 (green crystals, a complex of uranium (IV) with more ionic bonds). The Nobel Prize for Ernst Otto Fischer and Geoffrey Wilkinson in 1973 recognized the sensational discovery of the first two complexes and the resulting organometallic complex chemistry.


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