Paddlane

Last updated April 30, 2019

In organic chemistry, paddlane is any member of a class of tricyclic saturated hydrocarbons having two bridgehead carbon atoms joined by four bridges. The name derives from a supposed resemblance of the molecule to a paddle wheel: namely, the rings would be the propeller's blades, and the shared carbon atoms would be its axis.

Organic chemistry subdiscipline within chemistry involving the scientific study of carbon-based compounds, hydrocarbons, and their derivatives

Organic chemistry is a subdiscipline of chemistry that studies the structure, properties and reactions of organic compounds, which contain carbon in covalent bonding. Study of structure determines their chemical composition and formula. Study of properties includes physical and chemical properties, and evaluation of chemical reactivity to understand their behavior. The study of organic reactions includes the chemical synthesis of natural products, drugs, and polymers, and study of individual organic molecules in the laboratory and via theoretical study.

Polycyclic compound chemical compounds having more than one ring

In the field of organic chemistry, a polycyclic compound is an organic compound featuring several closed rings of atoms, primarily carbon. These ring substructures include cycloalkanes, aromatics, and other ring types. They come in sizes of three atoms and upward, and in combinations of linkages that include tethering, fusing, links via a single atom, bridged compounds, and longifolene. Though poly- literally means "many", there is some latitude in determining how many rings are required to be considered polycyclic; many smaller rings are described by specific prefixes, and so while it can refer to these, the title term is used with most specificity when these alternative names and prefixes are unavailable.

In organic chemistry, an alkane, or paraffin (a historical name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon–carbon bonds are single. Alkanes have the general chemical formula C_nH_2n+2. The alkanes range in complexity from the simplest case of methane (CH₄), where n = 1 (sometimes called the parent molecule), to arbitrarily large and complex molecules, like pentacontane (C₅₀H₁₀₂) or 6-ethyl-2-methyl-5-(1-methylethyl) octane, an isomer of tetradecane (C₁₄H₃₀).

Systematically named tricyclo [m.n.o.p^1,m+2]alkanes,^[1] these compounds have been referred to as [m.n.o.p]paddlanes. The notation [m.n.o.p]paddlane means the member of the family whose rings have m, n, o, and p carbons, not counting the two bridgeheads; or m + 2, n + 2, o + 2, and p + 2 carbons, counting them. The chemical formula is therefore C_2+m+n+o+pH_2(m+n+o+p). When p = 0, the compounds are propellanes.

In organic chemistry, propellane is any member of a class of polycyclic hydrocarbons, whose carbon skeleton consists of three rings of carbon atoms sharing a common carbon–carbon covalent bond. The name derives from a supposed resemblance of the molecule to a propeller: namely, the rings would be the propeller's blades, and the shared C–C bond would be its axis. The concept was introduced in 1966 by D. Ginsburg Propellanes with small cycles are highly strained and unstable, and are easily turned into polymers with interesting structures, such as staffanes. Partly for these reasons, they have been the object of much research. In the literature, the bond shared by the three cycles is usually called the "bridge"; the shared carbon atoms are then the "bridgeheads". The notation [x.y.z]propellane means the member of the family whose rings have x, y, and z carbons, not counting the two bridgeheads; or x + 2, y + 2, and z + 2 carbons, counting them. The chemical formula is therefore C_2+x+y+zH_2(x+y+z). The minimum value for x, y, and z is 1, meaning a 3-carbon ring.There is no structural ordering between the rings, so, for example, [1.3.2]propellane is the same substance as [3.2.1]propellane. Therefore, it is customary to sort the indices in decreasing order, x ≥ y ≥ z.

Compounds

[1.1.1.1]Paddlane 1111paddlane.svg — [1.1.1.1]Paddlane

The best known paddlane is [1.1.1.1]paddlane which can be seen as a precursor to octahedrane (C₆), an allotrope of elemental carbon.

A Platonic hydrocarbon is a hydrocarbon (molecule) whose structure matches one of the five Platonic solids, with carbon atoms replacing its vertices, carbon–carbon bonds replacing its edges, and hydrogen atoms as needed.

The American chemist Philip Eaton, famous for being the first to synthesize the "impossible" cubane molecule, has conducted studies for the synthesis of [2.2.2.2]paddlane.^[2] The first mention of paddlane goes back to 1973.^[3]

Philip E. Eaton is a Professor Emeritus of Chemistry at the University of Chicago. He and his fellow researchers were the first to synthesize the "impossible" cubane molecule in 1964.

Cubane (C₈H₈) is a synthetic hydrocarbon molecule that consists of eight carbon atoms arranged at the corners of a cube, with one hydrogen atom attached to each carbon atom. A solid crystalline substance, cubane is one of the Platonic hydrocarbons and a member of the prismanes. It was first synthesized in 1964 by Philip Eaton and Thomas Cole. Before this work, researchers believed that cubic carbon-based molecules would be too unstable to exist. The cubic shape requires the carbon atoms to adopt an unusually sharp 90° bonding angle, which would be highly strained as compared to the 109.45° angle of a tetrahedral carbon. Once formed, cubane is quite kinetically stable, due to a lack of readily available decomposition paths. It is the simplest hydrocarbon with octahedral symmetry.

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A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ellipsoid, tube, or many other shapes and sizes. Graphene, which is a flat mesh of regular hexagonal rings, can be seen as an extreme member of the family.

Monosaccharides, also called simple sugars, are the simplest form of sugar and the most basic units of carbohydrates. They cannot be further hydrolyzed to simpler chemical compounds. The general formula is C^_nH^_2nO^_n. They are usually colorless, water-soluble, and crystalline solids. Some monosaccharides have a sweet taste.

Cyclopropane is the cycloalkane molecule with the molecular formula C₃H₆, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms resulting in D_3h molecular symmetry. The small size of the ring creates substantial ring strain in the structure.

Octanitrocubane (molecular formula: C₈(NO₂)₈) is a high explosive that, like TNT, is shock-insensitive (not readily detonated by shock). The octanitrocubane molecule has the same chemical structure as cubane (C₈H₈) except that each of the eight hydrogen atoms is replaced by a nitro group (NO₂).

Adamantane is a colorless, crystalline chemical compound with a camphor-like odor. With a formula C₁₀H₁₆, it is a cycloalkane and also the simplest diamondoid. Adamantane molecules consists of three connected cyclohexane rings arranged in the "armchair" configuration. It is unique in that it is both rigid and virtually stress-free. Adamantane is the most stable among all the isomers with formula C₁₀H₁₆, which include the somewhat similar twistane. The spatial arrangement of carbon atoms in the adamantane molecule is the same as in the diamond crystal. This motivates the name adamantane, which is derived from the Greek adamantinos (relating to steel or diamond).

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, or heterocyclic, like DABCO. Moreover, the two rings can both be aliphatic, or can be aromatic, or a combination of aliphatic and aromatic.

Dodecahedrane is a chemical compound, a hydrocarbon with formula C
20H
20, whose carbon atoms are arranged as the vertices (corners) of a regular dodecahedron. Each carbon is bound to three neighbouring carbon atoms and to a hydrogen atom. This compound is one of the three possible Platonic hydrocarbons, the other two being cubane and tetrahedrane.

In organic chemistry, ring strain is a type of instability that exists when bonds in a molecule form angles that are abnormal. Strain is most commonly discussed for small rings such as cyclopropanes and cyclobutanes, whose internal angles are substantially smaller than the idealized value of approximately 109°. Because of their high strain, the heat of combustion for these small rings is elevated.

Prismane or 'Ladenburg benzene' is a polycyclic hydrocarbon with the formula C₆H₆. It is an isomer of benzene, specifically a valence isomer. Prismane is far less stable than benzene. The carbon (and hydrogen) atoms of the prismane molecule are arranged in the shape of a six-atom triangular prism—this compound is the parent and simplest member of the prismanes class of molecules. Albert Ladenburg proposed this structure for the compound now known as benzene. The compound was not synthesized until 1973.

Bredt's rule is an empirical observation in organic chemistry that states that a double bond cannot be placed at the bridgehead of a bridged ring system, unless the rings are large enough. The rule is named after Julius Bredt, who first discussed it in 1902 and codified it in 1924. It primarily relates to bridgeheads with carbon-carbon and carbon-nitrogen double bonds.

Tetrahedral molecular geometry Central atom with four substituents located at the corners of a tetrahedron

In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos⁻¹(−⅓) = 109.4712206...° ≈ 109.5° when all four substituents are the same, as in methane (CH₄) as well as its heavier analogues. Methane and other perfectly symmetrical tetrahedral molecules belong to point group T_d, but most tetrahedral molecules have lower symmetry. Tetrahedral molecules can be chiral.

Dicarbon monoxide (C₂O) is a molecule that contains two carbon atoms and one oxygen atom. It is a linear molecule that, because of its simplicity, is of interest in a variety of areas. It is, however, so extremely reactive that it is not encountered in everyday life. It is classified as a cumulene and an oxocarbon.

In the analysis of the molecular formula of organic molecules, the degree of unsaturation is a calculation that determines the total number of rings and π bonds. A formula is used in organic chemistry to help draw chemical structures. It does not give any information about those components individually—the specific number of rings, or of double bonds, or of triple bonds. The final structure is verified with use of NMR, mass spectrometry and IR spectroscopy, as well as qualitative inspection. It is based on comparing the actual molecular formula to what would be a possible formula if the structure were saturated—having no rings and containing only σ bonds—with all atoms having their standard valence.

A bridged compound is a chemical compound, generally an organic compound, but also possibly inorganic, that has two or more rings that contains a bridge—a single atom or an unbranched chain of atoms that connect two "bridgehead" atoms. The bridgehead atoms are defined as any atom that is not a hydrogen, and that is part of the skeletal framework of the molecule that is bonded to three or more other skeletal atoms. Clayden simplifies this description, saying that bridged bicyclic compounds "are just what the name implies—[molecules in which] a bridge of [an atom or of atoms] is thrown across from one side of the ring to the other," examples of which are shown at left and right, and below. The presence of the bridge connecting the bridgehead atoms, which are most often two non-adjacent atoms, distinguishes bridged compounds from fused ring compounds that have two rings linked by two adjacent atoms, and from spiro compounds that have two rings linked by a single atom.

[1.1.1]Propellane is an organic compound, the simplest member of the propellane family. It is a hydrocarbon with formula C₅H₆ or C₂(CH₂)₃. The molecular structure consists of three rings of three carbon atoms each, sharing one C–C bond.

[2.2.2]Propellane, formally tricyclo[2.2.2.0^1,4]octane is an organic compound, a member of the propellane family. It is a hydrocarbon with formula C₈H₁₂, or C₂(C₂H₄)₃. Its molecule has three rings with four carbon atoms each, sharing one C–C bond.

Pagodane is an organic compound with formula C^₂₀H^₂₀ whose carbon skeleton was said to resemble a pagoda, hence the name. It is a polycyclic hydrocarbon whose molecule has the D_2h point symmetry group. The compound is a highly crystalline solid that melts at 243 °C, is barely soluble in most organic solvents and moderately soluble in benzene and chloroform. It sublimes at low pressure.

The charge-shift bond has been proposed as a new class of chemical bond that sits alongside the three familiar families of covalent, ionic bonds, and metallic bonds where electrons are shared or transferred respectively. The charge shift bond derives its stability from the resonance of ionic forms rather than the covalent sharing of electrons which are often depicted as having electron density between the bonded atoms. A feature of the charge shift bond is that the predicted electron density between the bonded atoms is low. It has long been known from experiment that the accumulation of electronic charge between the bonded atoms is not necessarily a feature of covalent bonds. An example where charge shift bonding has been used to explain the low electron density found experimentally is in the central bond between the inverted tetrahedral carbons in [1.1.1]propellanes. Theoretical calculations on a range of molecules have indicated that a charge shift bond is present, a striking example being fluorine, F₂, which is normally described as having a typical covalent bond.

References

↑ IUPAC , Compendium of Chemical Terminology , 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) " paddlanes ". doi : 10.1351/goldbook.P04395
↑ Eaton, Philip E.; Leipzig, Bernard D. (1983). "Toward tricyclo[2.2.2.2]decane. 1. [n.2.2.2]Paddlane systems, n = 10–14". Journal of the American Chemical Society. 105 (6): 1656. doi:10.1021/ja00344a042.
↑ Hahn, E. H.; Bohm, H.; Ginsburg, D. (1973). "The synthesis of paddlanes: Compounds in which quaternary bridgehead carbons are joined by four chains". Tetrahedron Letters. 14 (7): 507. doi:10.1016/S0040-4039(01)95684-9.

Paddlane

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Compounds

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