Aromatic compounds or arenes usually refers to organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were understood. The current definition of aromatic compounds does not have any relation to their odor. Aromatic compounds are now defined as cyclic compounds satisfying Hückel's Rule. Aromatic compounds have the following general properties:
In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or in the terminal position. Terminal alkenes are also known as α-olefins.
The structural formula of a chemical compound is a graphic representation of the molecular structure, showing how the atoms are possibly arranged in the real three-dimensional space. The chemical bonding within the molecule is also shown, either explicitly or implicitly. Unlike other chemical formula types, which have a limited number of symbols and are capable of only limited descriptive power, structural formulas provide a more complete geometric representation of the molecular structure. For example, many chemical compounds exist in different isomeric forms, which have different enantiomeric structures but the same molecular formula. There are multiple types of ways to draw these structural formulas such as: Lewis structures, condensed formulas, skeletal formulas, Newman projections, Cyclohexane conformations, Haworth projections, and Fischer projections.
In theoretical chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in a molecule, which in general lowers the overall energy of the molecule and increases stability. It is conventionally represented as having alternating single and multiple bonds. Lone pairs, radicals or carbenium ions may be part of the system, which may be cyclic, acyclic, linear or mixed. The term "conjugated" was coined in 1899 by the German chemist Johannes Thiele.
In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August Wilhelm Hofmann in 1855. There is no general relationship between aromaticity as a chemical property and the olfactory properties of such compounds.
In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures into a resonance hybrid in valence bond theory. It has particular value for analyzing delocalized electrons where the bonding cannot be expressed by one single Lewis structure. The resonance hybrid is the accurate structure for a molecule or ion; it is an average of the theoretical contributing structures.
In organic chemistry, Hückel's rule predicts that a planar ring molecule will have aromatic properties if it has 4n + 2 π-electrons, where n is a non-negative integer. The quantum mechanical basis for its formulation was first worked out by physical chemist Erich Hückel in 1931. The succinct expression as the 4n + 2 rule has been attributed to W. v. E. Doering (1951), although several authors were using this form at around the same time.
Antiaromaticity is a chemical property of a cyclic molecule with a π electron system that has higher energy, i.e., it is less stable due to the presence of 4n delocalised electrons in it, as opposed to aromaticity. Unlike aromatic compounds, which follow Hückel's rule and are highly stable, antiaromatic compounds are highly unstable and highly reactive. To avoid the instability of antiaromaticity, molecules may change shape, becoming non-planar and therefore breaking some of the π interactions. In contrast to the diamagnetic ring current present in aromatic compounds, antiaromatic compounds have a paramagnetic ring current, which can be observed by NMR spectroscopy.
In organic chemistry, a methine group or methine bridge is a trivalent functional group =CH−, derived formally from methane. It consists of a carbon atom bound by two single bonds and one double bond, where one of the single bonds is to a hydrogen. The group is also called methyne or methene, but its IUPAC systematic name is methylylidene or methanylylidene.
A silabenzene is a heteroaromatic compound containing one or more silicon atoms instead of carbon atoms in benzene. A single substitution gives silabenzene proper; additional substitutions give a disilabenzene, trisilabenzene, etc.
Simple aromatic rings, also known as simple arenes or simple aromatics, are aromatic organic compounds that consist only of a conjugated planar ring system. Many simple aromatic rings have trivial names. They are usually found as substructures of more complex molecules. Typical simple aromatic compounds are benzene, indole, and pyridine.
1,3,5,7-Cyclooctatetraene (COT) is an unsaturated derivative of cyclooctane, with the formula C8H8. It is also known as [8]annulene. This polyunsaturated hydrocarbon is a colorless to light yellow flammable liquid at room temperature. Because of its stoichiometric relationship to benzene, COT has been the subject of much research and some controversy.
Cyclodecapentaene or [10]annulene is an annulene with molecular formula C10H10. This organic compound is a conjugated 10 pi electron cyclic system and according to Huckel's rule it should display aromaticity. It is not aromatic, however, because various types of ring strain destabilize an all-planar geometry.
Cyclooctadecanonaene or [18]annulene is an organic compound with chemical formula C
18H
18. It belongs to the class of highly conjugated compounds known as annulenes and is aromatic. The usual isomer that [18]annulene refers to is the most stable one, containing six interior hydrogens and twelve exterior ones, with the nine formal double bonds in the cis,trans,trans,cis,trans,trans,cis,trans,trans configuration. It is reported to be a red-brown crystalline solid.
Cycloheptatriene (CHT) is an organic compound with the formula C7H8. It is a closed ring of seven carbon atoms joined by three double bonds (as the name implies) and four single bonds. This colourless liquid has been of recurring theoretical interest in organic chemistry. It is a ligand in organometallic chemistry and a building block in organic synthesis. Cycloheptatriene is not aromatic, as reflected by the nonplanarity of the methylene bridge (-CH2-) with respect to the other atoms; however the related tropylium cation is.
In organic chemistry, annulynes or dehydroannulenes are conjugated monocyclic hydrocarbons with alternating single and double bonds in addition to at least one triple bond.
A cyclic compound is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where all the atoms are carbon, none of the atoms are carbon, or where both carbon and non-carbon atoms are present. Depending on the ring size, the bond order of the individual links between ring atoms, and their arrangements within the rings, carbocyclic and heterocyclic compounds may be aromatic or non-aromatic; in the latter case, they may vary from being fully saturated to having varying numbers of multiple bonds between the ring atoms. Because of the tremendous diversity allowed, in combination, by the valences of common atoms and their ability to form rings, the number of possible cyclic structures, even of small size numbers in the many billions.
Cyclotetradecaheptaene, often referred to as [14]annulene, is a hydrocarbon with molecular formula C14H14, which played an important role in the development of criteria (Hückel's rule) for aromaticity, a stabilizing property of central importance in physical organic chemistry. It forms dark-red needle-like crystals.
1,6-Methano[10]annulene (also known as 1,6-methanonaphthalene or homonaphthalene) is an aromatic hydrocarbon with chemical formula C11H10. It was the first stable aromatic compound based on the cyclodecapentaene system to be discovered.
Bicyclo[6.2.0]decapentaene is a bicyclic organic compound and an isomer of naphthalene and azulene.
![Structure and AFM image of a hexadehydrotribenzo[12]annulene Dehydrobenzoannulene.jpg](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f9/Dehydrobenzoannulene.jpg/310px-Dehydrobenzoannulene.jpg)
