Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. 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 with their odor.
In organic chemistry, hydrocarbons are divided into two classes: aromatic compounds and aliphatic compounds. Aliphatic compounds can be saturated like hexane, or unsaturated, like hexene and hexyne. Open-chain compounds, whether straight or branched, and which contain no rings of any type, are always aliphatic. Cyclic compounds can be aliphatic if they are not aromatic.
A metallocene is a compound typically consisting of two cyclopentadienyl anions (C
5H−
5, abbreviated Cp) bound to a metal center (M) in the oxidation state II, with the resulting general formula (C5H5)2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride or vanadocene dichloride. Certain metallocenes and their derivatives exhibit catalytic properties, although metallocenes are rarely used industrially. Cationic group 4 metallocene derivatives related to [Cp2ZrCH3]+ catalyze olefin polymerization.
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms. Study of structure determines their structural 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.
In organic chemistry, the cycloalkanes are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing a single ring, and all of the carbon-carbon bonds are single. The larger cycloalkanes, with more than 20 carbon atoms are typically called cycloparaffins. All cycloalkanes are isomers of alkenes.
In chemistry, aromaticity means a molecule has a cyclic (ring-shaped) structure with pi bonds in resonance. Aromatic rings give increased stability compared to saturated compounds having single bonds, and other geometric or connective non-cyclic arrangements with the same set of atoms. Aromatic rings are very stable and do not break apart easily. Organic compounds that are not aromatic are classified as aliphatic compounds—they might be cyclic, but only aromatic rings have enhanced stability. The term aromaticity with this meaning is historically related to the concept of having an aroma, but is a distinct property from that meaning.
A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. PAHs are uncharged, non-polar and planar. Many are colorless. Many of them are found in coal and in oil deposits, and are also produced by the incomplete combustion of organic matter—for example, in engines and incinerators or when biomass burns in forest fires.
3-Methylenecyclopropene, also called methylenecyclopropene or triafulvene, is a hydrocarbon with chemical formula C4H4. It is a colourless gas that polymerizes readily as a liquid or in solution but is stable as a gas. This highly strained and reactive molecule was synthesized and characterized for the first time in 1984, and has been the subject of considerable experimental and theoretical interest. It is an example of a cross-conjugated alkene, being composed of cyclopropene with an exocyclic double bond attached.
An alkyne trimerisation is a [2+2+2] cycloaddition reaction in which three alkyne units react to form a benzene ring. The reaction requires a metal catalyst. The process is of historic interest as well as being applicable to organic synthesis. Being a cycloaddition reaction, it has high atom economy. Many variations have been developed, including cyclisation of mixtures of alkynes and alkenes as well as alkynes and nitriles.
Sumanene is a polycyclic aromatic hydrocarbon and of scientific interest because the molecule can be considered a fragment of buckminsterfullerene. Suman means "sunflower" in both Hindi and Sanskrit. The core of the arene is a benzene ring and the periphery consists of alternating benzene rings (3) and cyclopentadiene rings (3). Unlike fullerene, sumanene has benzyl positions which are available for organic reactions.
In organic chemistry, a cycloalkyne is the cyclic analog of an alkyne. A cycloalkyne consists of a closed ring of carbon atoms containing one or more triple bonds. Cycloalkynes have a general formula CnH2n−4. Because of the linear nature of the C−C≡C−C alkyne unit, cycloalkynes can be highly strained and can only exist when the number of carbon atoms in the ring is great enough to provide the flexibility necessary to accommodate this geometry. Large alkyne-containing carbocycles may be virtually unstrained, while the smallest constituents of this class of molecules may experience so much strain that they have yet to be observed experimentally. Cyclooctyne is the smallest cycloalkyne capable of being isolated and stored as a stable compound. Despite this, smaller cycloalkynes can be produced and trapped through reactions with other organic molecules or through complexation to transition metals.
Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp3 hybridized carbon atom. Although this sp3 center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties associated with aromatic compounds are still observed for such compounds. This formal discontinuity is apparently bridged by p-orbital overlap, maintaining a contiguous cycle of π electrons that is responsible for this preserved chemical stability.
In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by haptic, covalent bonds to two arene (ring) ligands. The arenes have the formula CnHn, substituted derivatives and heterocyclic derivatives. Because the metal is usually situated between the two rings, it is said to be "sandwiched". A special class of sandwich complexes are the metallocenes.
Cyclooctane is a cycloalkane with the molecular formula (CH2)8. It is a simple colourless hydrocarbon, but it is often a reference compound for saturated eight-membered ring compounds in general.
Basketene (IUPAC name: pentacyclo[4.4.0.02,5.03,8.04,7]dec-9-ene) is an organic compound with the formula C10H10. It is a polycyclic alkene and the dehydrogenated version of basketane, which was named for its structural similarity to a basket. Due to its hydrocarbon composition and unique structure, the chemical compound is of considerable interest to those examining energy surfaces of these (CH)10 cage molecules and what possible factors influence their minima. Additionally, the complex structure of this compound has intrigued researchers studying the chemistry of highly strained ring systems. Basketene and its family of derivatives also have important chemical and physical properties. These molecules all tend to have a high standard enthalpy of formation, combined with their high density, leading to possible uses in explosives.
Benzvalene is an organic compound and one of several isomers of benzene. It was first synthesized in 1967 by K. E. Wilzbach et al. via photolysis of benzene and the synthesis was later improved by Thomas J. Katz et al.
In organometallic chemistry, bent metallocenes are a subset of metallocenes. In bent metallocenes, the ring systems coordinated to the metal are not parallel, but are tilted at an angle. A common example of a bent metallocene is Cp2TiCl2. Several reagents and much research is based on bent metallocenes.
Thermal rearrangements of aromatic hydrocarbons are considered to be unimolecular reactions that directly involve the atoms of an aromatic ring structure and require no other reagent than heat. These reactions can be categorized in two major types: one that involves a complete and permanent skeletal reorganization (isomerization), and one in which the atoms are scrambled but no net change in the aromatic ring occurs (automerization). The general reaction schemes of the two types are illustrated in Figure 1.
Cyclopentyne is a cycloalkyne containing five carbon atoms in the ring. Due to the ideal bond angle of 180° at each atom of the alkyne but the structural requirement that the bonds form a ring, this chemical is a highly strained structure, and the triple bond is highly reactive. The triple bond easily undergoes both [2+2] and [4+2] cycloaddition reactions. Unlike benzyne, which undergoes a [2+2] addition with loss of stereochemistry at the alkene partner, cyclopentyne reacts with alkenes with retention of geometry of the partner, an example of the relevance of orbital symmetry even for highly reactive structures. The structure can also form a π complex with lithium cations, which affects the cycloaddition reactivity. It can even interact strongly enough with copper species to form a novel type of metallacycle.
Cyclooctyne is the cycloalkyne with a formula C
8H
12. Its molecule has a ring of 8 carbon atoms, connected by seven single bonds and one triple bond.
