"than 1 sigma bond between any two atoms. Molecules with rings have additional sigma bonds, such as benzene rings, which have 6 C−C sigma bonds within the ring for 6 carbon atoms. The anthracene molecule, CH, has three rings so that the rule gives the number of sigma bonds as 24 + 3 − 1 = 26. In this case there are 16 C−C sigma bonds and 10 C−H bonds. Sigma bond In chemistry, sigma bonds (σ bonds) are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most simply"
"benzene paper; its 150th anniversary was also marked. The cyclic nature of benzene was confirmed crystallographically by Kathleen Lonsdale in 1929. X-ray diffraction confirms that all six carbon-carbon bonds in benzene are the same length, 140 pm (1.40 Å) – intermediate between the bond lengths of single (154 pm) and double (134 pm) carbon-carbon bonds. This is consistent with delocalization of the electrons from the double bonds in Kekulé's structures equally between each of the six carbon atoms which form a planar ring. The molecular orbital theory description involves the formation of three delocalized π orbitals spanning all six carbon"
"as such. The nature of its bonding was first recognized by August Kekulé in the 19th century. Each carbon atom in the hexagonal cycle has four electrons to share. One goes to the hydrogen atom, and one to each of the two neighbouring carbons. This leaves one electron to share with one of the two neighbouring carbon atoms, thus creating a double bond with one carbon and leaving a single bond with the other, which is why the benzene molecule is drawn with alternating single and double bonds around the hexagon. The structure is alternatively illustrated as a circle around"
"the two contributing structures of benzene, all single and double bonds are interchanged. Bond lengths can be measured, for example using X-ray diffraction. The average length of a C–C single bond is 154 pm; that of a C=C double bond is 133 pm. In localized cyclohexatriene, the carbon–carbon bonds should be alternating 154 and 133 pm. Instead, all carbon–carbon bonds in benzene are found to be about 139 pm, a bond length intermediate between single and double bond. This mixed single and double bond (or triple bond) character is typical for all molecules in which bonds have a different bond"
"the ring plane. All carbon-carbon bonds in benzene are chemically equivalent. In MO theory this is a direct consequence of the fact that the three molecular π orbitals combine and evenly spread the extra six electrons over six carbon atoms. In molecules such as methane, , the eight valence electrons are found in four MOs that are spread out over all five atoms. However, it is possible to transform the MOs into four localized sp orbitals. Linus Pauling, in 1931, hybridized the carbon 2s and 2p orbitals so that they pointed directly at the hydrogen 1s basis functions and featured"
"ground state, but may be occupied in excited states. Similarly benzene with six carbon atoms has three bonding pi orbitals and three antibonding pi orbitals. Since each carbon atom contributes one electron to the π-system of benzene, there are six pi electrons which fill the three lowest-energy pi molecular orbitals (the bonding pi orbitals). Antibonding orbitals are also important for explaining chemical reactions in terms of molecular orbital theory. Roald Hoffmann and Kenichi Fukui shared the 1981 Nobel Prize in Chemistry for their work and further development of qualitative molecular orbital explanations for chemical reactions. Antibonding molecular orbital In chemical"
"undertaking the work, saying: ""It is all about the challenge and the possibility to astonish chemists about what can be possible."" Hexamethylbenzene Hexamethylbenzene, also known as mellitene, is a hydrocarbon with the molecular formula CH and the condensed structural formula C(CH). It is an aromatic compound and a derivative of benzene, where benzene's six hydrogen atoms have each been replaced by a methyl group. In 1929 Kathleen Lonsdale reported the crystal structure of hexamethylbenzene, demonstrating that the central ring is hexagonal and flat and thereby ending an ongoing debate about the physical parameters of the benzene system. This was a"
"the 2s σ. From the hydrogen, its valence 1s electron interacts with the 2p electrons of fluorine. This molecule is diamagnetic and has a bond order of one. Carbon dioxide, , is a linear molecule with a total of sixteen bonding electrons in its valence shell. Carbon is the central atom of the molecule and a principal axis, the z-axis, is visualized as a single axis that goes through the center of carbon and the two oxygens atoms. For convention, blue atomic orbital lobes are positive phases, red atomic orbitals are negative phases, with respect to the wave function from"
"the electron, proposed three equivalent electrons between each pair of carbon atoms in benzene. An explanation for the exceptional stability of benzene is conventionally attributed to Sir Robert Robinson, who was apparently the first (in 1925) to coin the term ""aromatic sextet"" as a group of six electrons that resists disruption. In fact, this concept can be traced further back, via Ernest Crocker in 1922, to Henry Edward Armstrong, who in 1890 wrote ""the (six) centric affinities act within a cycle...benzene may be represented by a double ring (""sic"") ... and when an additive compound is formed, the inner cycle"
"Dewar benzene Dewar benzene (also spelled ""dewarbenzene"") or bicyclo[2.2.0]hexa-2,5-diene is a bicyclic isomer of benzene with the molecular formula CH. The compound is named after James Dewar who included this structure in a list of possible CH structures in 1867. However, he did not propose it as the structure of benzene, and in fact he supported the correct structure previously proposed by August Kekulé in 1865. Unlike benzene, Dewar benzene is not flat because the carbons where the rings join are bonded to four atoms rather than three. These carbons tend toward tetrahedral geometry, and the two cyclobutene rings make"
"first time in 1856. Historic interest in benzene arose from the uncertainty over its structure and reactivity. It was well established that it had a carbon to hydrogen ratio of 1:1 which suggested the presence of double or triple bond carbon-to-carbon bonds, yet such unsaturated compounds typically undergo addition reactions, which benzene does not. Numerous potential structures were proposed, including by Claus, Dewar, Ladenburg, Armstrong, and Thiele. The most influential proposal was that of Kekulé who in 1865 suggested a cyclic structure of six carbon atoms with alternating single and double bonds Kekulé based his argument on the now well-known"
"Hexamethylbenzene Hexamethylbenzene, also known as mellitene, is a hydrocarbon with the molecular formula CH and the condensed structural formula C(CH). It is an aromatic compound and a derivative of benzene, where benzene's six hydrogen atoms have each been replaced by a methyl group. In 1929 Kathleen Lonsdale reported the crystal structure of hexamethylbenzene, demonstrating that the central ring is hexagonal and flat and thereby ending an ongoing debate about the physical parameters of the benzene system. This was a historically significant result, both for the field of X-ray crystallography and for understanding aromaticity. The compound can be prepared by reacting"
"unit. This concept, devised by Rémi Chauvin in 1995, is aimed at introducing new chemical properties for existing chemical motifs. Two distinct expansions of benzene can be called ""carbo""-benzene (CH): One (above right) expands each C-H bond to C-C≡C-H, making hexaethynylbenzene, a substituted benzene derivative. One (above left) expands each C=C and C≡C bond of the benzene core, making 1,2,4,5,7,8,10,11,13,14,16,17-dodecadehydro[18]annulene. An analog of this molecule, with the hydrogen atoms replaced by phenyl groups, 3,6,9,12,15,18-hexaphenyl-1,2,4,5,7,8,10,11,13,14,16,17-dodecadehydro[18]annulene, is stable. Its proton NMR spectrum shows that the phenyl protons are shifted downfield compared to a proton position in benzene itself (chemical shift position for"
"structures, such as with the two resonance structures of benzene. These molecules cannot be found in either one of these representations, with the longer single bonds in one location and the shorter double bond in another (See Theory below). Rather, the molecule exhibits bond lengths in between those of single and double bonds. This commonly seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds (cyclohexatriene), was developed by August Kekulé (see History section below). The model for benzene consists of two resonance forms, which corresponds to"
"for the contributing structure. The complete hydrogenation of benzene to cyclohexane via 1,3-cyclohexadiene and cyclohexene is exothermic; 1 mole of benzene delivers 208.4 kJ (49.8 kcal). Hydrogenation of one mole of double bonds delivers 119.7 kJ (28.6 kcal), as can be deduced from the last step, the hydrogenation of cyclohexene. In benzene, however, 23.4 kJ (5.6 kcal) are needed to hydrogenate one mole of double bonds. The difference, being 143.1 kJ (34.2 kcal), is the empirical resonance energy of benzene. Because 1,3-cyclohexadiene also has a small delocalization energy (7.6 kJ or 1.8 kcal/mol) the net resonance energy, relative to the"
"the peculiar molecular and chemical properties known as aromaticity. To accurately reflect the nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms. Derivatives of benzene occur sufficiently often as a component of organic molecules that the Unicode Consortium has allocated a symbol in the Miscellaneous Technical block with the code U+232C (⌬) to represent it with three double bonds, and U+23E3 (⏣) for a delocalized version. Many important chemical compounds are derived from benzene by replacing one or more of its hydrogen atoms with another functional group. Examples of simple benzene"
"Cubane Cubane (CH) 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"
"structure, but rather a resonance hybrid of different structures, such as with the two resonance structures of benzene. These molecules cannot be found in either one of these representations, with the longer single bonds in one location and the shorter double bond in another (see Theory below). Rather, the molecule exhibits bond lengths in between those of single and double bonds. This commonly seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds (cyclohexatriene), was developed by August Kekulé (see History below). The model for benzene consists"
"bonded by sharing more than one pair of electrons. The common bonds to carbon are single, double and triple bonds. Single bonds are most common and are represented by a single, solid line between two atoms in a skeletal formula. Double bonds are denoted by two parallel lines, and triple bonds are shown by three parallel lines. In more advanced theories of bonding, non-integer values of bond order exist. In these cases, a combination of solid and dashed lines indicate the integer and non-integer parts of the bond order, respectively. In recent years, benzene is generally depicted as a hexagon"
"2-Butene 2-Butene is an acyclic alkene with four carbon atoms. It is the simplest alkene exhibiting ""cis""/""trans""-isomerism (also known as (""E""/""Z"")-isomerism); that is, it exists as two geometric isomers ""cis""-2-butene ((""Z"")-2-butene) and ""trans""-2-butene ((""E"")-2-butene). It is a petrochemical, produced by the catalytic cracking of crude oil or the dimerization of ethylene. Its main uses are in the production of gasoline (petrol) and butadiene, although some 2-butene is also used to produce the solvent butanone via hydration to 2-butanol followed by oxidation. The two isomers are extremely difficult to separate by distillation because of the proximity of their boiling points (~1"
"the orbital resonance images of a single hexacene molecules using scanning tunneling microscopy. They synthesized hexacene in-situ via deoxygenation from an air-stable precursor. Hexacene Hexacene is an aromatic molecule consisting of six linearly-fused benzene rings. Hexacene and its derivatives are investigated for potential applications as organic semiconductor. Hexacene is one of a series of linear acenes, the previous one being pentacene (five fused benzene rings) and the next one being heptacene (seven fused benzene rings). Hexacene is very unstable, being highly reactive in the 6, 15 positions due to pi electron localization. Its spectra must be collected on freshly purified"
"final 6 carbon atoms are inserted in a nucleophilic addition to the ketone groups of the carbanion 10 generated from allyltrimethylsilane 9 and ""n""-butyllithium. In the next step the vinyl silane 11 reacts with peracetic acid in acetic acid in a radical substitution to the dilactone 12 followed by an intramolecular Friedel-Crafts alkylation with phosphorus pentoxide to diketone 13. This molecule contains all required 20 carbon atoms and is also symmetrical which facilitates the construction of the remaining 5 carbon-carbon bonds. Reduction of the double bonds in 13 to 14 is accomplished with hydrogenation with palladium on carbon and that"
"Hexadecene Hexadecene, also known as cetene, is an alkene containing 16 carbon atoms, with a molecular formula of CH. There are many different structural isomers of hexadecene, depending on the location of the double carbon bond. 1-Hexadecene is a linear alpha olefin due to the location of its double bond at the primary, or alpha, position (between the first two carbon atoms). 1-Hexadecene is a clear liquid at room temperature. 1-Hexadecene is more reactive than other hexadecene isomers, giving it a number of useful applications. For instance, 1-hexadecane is widely used as a surfactant in lubricating fluid, a drilling fluid"
"backbone chain of the molecules. Other organic compounds have the formula CH, namely cyclobutane and methylcyclopropane, but are not alkenes and do not fall under the name ""butene"". There are also cyclic alkenes with four carbon atoms overall such as cyclobutene and two isomers of methylcyclopropene, but they do not have the formula CH and are not discussed here. All four of these isomers are gases at room temperature and pressure, but can be liquefied by lowering the temperature or raising the pressure on them, in a manner similar to pressurised butane. These gases are colourless, but do have distinct"
"contain two carbon atoms, six hydrogen atoms, and one oxygen atom. Some types of ionic compounds, however, cannot be written with entirely whole-number empirical formulas. An example is boron carbide, whose formula of CB is a variable non-whole number ratio with n ranging from over 4 to more than 6.5. When the chemical compound of the formula consists of simple molecules, chemical formulas often employ ways to suggest the structure of the molecule. There are several types of these formulas, including molecular formulas and condensed formulas. A molecular formula enumerates the number of atoms to reflect those in the molecule,"
"Olympicene Olympicene is an organic carbon based molecule formed of five rings, of which four are benzene rings, joined in the shape of the Olympic rings. The molecule was conceived in March 2010 as a way to celebrate the 2012 London Olympics by Graham Richards of University of Oxford and Antony Williams. It was first synthesized by researchers Anish Mistry and David Fox of the University of Warwick in the UK. Relative energies of olympicene and its isomers were first predicted from quantum electronic-structure computations by Andrew Valentine and David Mazziotti of the University of Chicago. Olympicene has 18 pi"
"of two resonance forms, which corresponds to the double and single bonds superimposing to produce six one-and-a-half bonds. Benzene is a more stable molecule than would be expected without accounting for charge delocalization. As is standard for resonance diagrams, the use of a double-headed arrow indicates that two structures are not distinct entities but merely hypothetical possibilities. Neither is an accurate representation of the ""actual"" compound, which is best represented by a hybrid (average) of these structures. A C=C bond is shorter than a C−C bond. Benzene is a regular hexagon—it is planar and all six carbon–carbon bonds have the"
"Pentacene Pentacene is a polycyclic aromatic hydrocarbon consisting of five linearly-fused benzene rings. This highly conjugated compound is an organic semiconductor. The compound generates excitons upon absorption of ultra-violet (UV) or visible light; this makes it very sensitive to oxidation. For this reason, this compound, which is a purple powder, slowly degrades upon exposure to air and light. Structurally, pentacene is one of the linear acenes, the previous one being tetracene (four fused benzene rings) and the next one being hexacene (six fused benzene rings). In August 2009, a group of researchers from IBM published experimental results of imaging a"
"Carbon Carbon (from ""coal"") is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Three isotopes occur naturally, C and C being stable, while C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity. Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon's abundance, its unique"
"20 kcal/mole. Proton NMR shows just one peak at 2,98 ppm and carbon NMR two at 32 ppm and 144 ppm. Superphane [2.2.2.2.2.2]( 1,2,3,4,5,6)Cyclophane or superphane is a 6-fold bridged cyclophane with all arene positions in the benzene dimer taken up by ethylene spacers. The compound has been of some scientific interest as a model for testing aromaticity and was first synthesised by Boekelheide in 1979. Superphane is the base compound for a large group of derivatives with structural variations. The analogs with 2 to 5 bridges are also known compounds. The benzene rings have been replaced by other aromatic"
"may be present in the mixture. The alkanes from pentane (CH) to octane (CH) are refined into gasoline, the ones from nonane (CH) to hexadecane (CH) into diesel fuel, kerosene and jet fuel. Alkanes with more than 16 carbon atoms can be refined into fuel oil and lubricating oil. At the heavier end of the range, paraffin wax is an alkane with approximately 25 carbon atoms, while asphalt has 35 and up, although these are usually cracked by modern refineries into more valuable products. The shortest molecules, those with four or fewer carbon atoms, are in a gaseous state at"
"The formation of elements with more than seven nucleons requires the fusion of three atoms of He-4 in the so-called triple alpha process, skipping over lithium, beryllium, and boron to produce carbon. Here are some values of the ratio of atomic mass to mass number: Direct comparison and measurement of the masses of atoms is achieved with mass spectrometry. The standard scientific unit used to quantify the amount of a substance in macroscopic quantities is the mole (symbol: mol), which is defined arbitrarily as the amount of a substance which has as many atoms or molecules as there are atoms"
"Hexacene Hexacene is an aromatic molecule consisting of six linearly-fused benzene rings. Hexacene and its derivatives are investigated for potential applications as organic semiconductor. Hexacene is one of a series of linear acenes, the previous one being pentacene (five fused benzene rings) and the next one being heptacene (seven fused benzene rings). Hexacene is very unstable, being highly reactive in the 6, 15 positions due to pi electron localization. Its spectra must be collected on freshly purified samples handled in an inert atmosphere such as nitrogen or argon. Only with very large substituents it is possible to isolate an hexacene"