# They undergo electrophilic substitution reactions and nucleophilic aromatic substitutions.

The two main types are electrophilic aromatic substitution when the active reagent is an electrophile and nucleophilic aromatic substitution when the reagent is a nucleophile.

In radical-nucleophilic aromatic substitution the active reagent is a radical.

The latter have high electron density and enter nucleophilic aromatic substitution only with very strong electron withdrawing groups.

This reaction takes place almost exclusively in aromatic hydrocarbons, where it is called electrophilic aromatic substitution.

An alternative to aromatic substitution is electrophilic aliphatic substitution.

Mechanism of electrophilic aromatic substitution

A pyrimidine has many properties in common with pyridine, as the number of nitrogen atoms in the ring increases the ring pi electrons become less energetic and electrophilic aromatic substitution gets more difficult while nucleophilic aromatic substitution gets easier.

Typical N values with s in parenthesis are-4. 47 ( 1. 32 ) for electrophilic aromatic substitution to toluene ( 1 ),-0. 41 ( 1. 12 ) for electrophilic addition to 1-phenyl-2-propene ( 2 ), and 0. 96 ( 1 ) for addition to 2-methyl-1-pentene ( 3 ),-0. 13 ( 1. 21 ) for reaction with triphenylallylsilane ( 4 ), 3. 61 ( 1. 11 ) for reaction with 2-methylfuran ( 5 ), + 7. 48 ( 0. 89 ) for reaction with isobutenyltributylstannane ( 6 ) and + 13. 36 ( 0. 81 ) for reaction with the enamine 7.

# REDIRECT Electrophilic aromatic substitution

Nucleophilic substitution reactions are commonplace in organic chemistry, and they can be broadly categorised as taking place at a saturated aliphatic carbon or at ( less often ) a saturated aromatic or other unsaturated carbon centre.

Second, he is describing electrophilic aromatic substitution, proceeding ( third ) through a Wheland intermediate, in which ( fourth ) the conjugation of the ring is broken.

Aromatic compounds undergo electrophilic aromatic substitution and nucleophilic aromatic substitution reactions, but not electrophilic addition reactions as happens with carbon-carbon double bonds.

Examples of non-benzene compounds with aromatic properties are furan, a heterocyclic compound with a five-membered ring that includes an oxygen atom, and pyridine, a heterocyclic compound with a six-membered ring containing one nitrogen atom.

# Aromatic hydrocarbons, also known as arenes, are hydrocarbons that have at least one aromatic ring.

Delocalization — bonding that involves more than one pair of atoms held together by one pair of electrons — is most familiar from the example of benzene C < sub > 6 </ sub > H < sub > 6 </ sub >, where six electrons from six carbon atoms are engaged in joint aromatic bonding.

Benzene is one of the best-known aromatic compounds as it is one of the simplest and most stable aromatics.

According to at least one Chinese culinary writer, Szechuan cuisine is composed of seven basic flavours: sour, pungent, hot, sweet, bitter, aromatic, and salty.

* In biochemical systems, the process of demethylation is often catalyzed by an enzyme such as one of the cytochrome P450 ( CYP ) family of liver enzymes and by fungal aromatic peroxygenases such as Agrocybe aegerita peroxygenase.

:" In a special compartment of the shrine now there showed-along with remains of ancient old rotten or moulded bandages, most likely byssus, besides pieces of aromatic resins and similar substances-numerous bones of three persons, which under the guidance of several present experts could be assembled into nearly complete bodies: the one in his early youth, the second in his early manhood, the third was rather aged.

It is a highly aromatic and flavorful herb with culinary and medicinal uses, and, along with the similar-tasting anise, is one of the primary ingredients of absinthe.

** Lustration ; this one day festival took place on the third day of the third moon ( dubbed the " double-three "), and traditionally was meant to dispel evil and wash away defilement in a river with scented aromatic orchis plants.

Book one describes the uses for aromatic oils, salves and ointments, trees and shrubs, and fleshy fruits, even if not aromatic.

Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group that is connected to an aromatic ring by a two-carbon chain (- CH < sub > 2 </ sub >- CH < sub > 2 </ sub >-).

Aromatic molecules are also able to interact with each other in an " edge-to-face " orientation: The slight positive charge of the substituents on the ring atoms of one molecule are attracted to the slight negative charge of the aromatic system on another molecule.

The four aromatic amino acids histidine, phenylalanine, tryptophan, and tyrosine each serve as one of the 20 basic building-blocks of proteins.

In heterocyclic aromatics ( heteroaromats ), one or more of the atoms in the aromatic ring is of an element other than carbon.

Most are aromatic evergreen trees or shrubs, but one or two genera such as Sassafras are deciduous, and Cassytha is a genus of parasitic vines.

An aromatic amine is an amine with an aromatic substituent-that is-NH < sub > 2 </ sub >,-NH-or nitrogen group ( s ) attached to an aromatic hydrocarbon, whose structure usually contains one or more benzene rings.

They contain one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character.

Benzene, one of the simplest aromatic hydrocarbons, for example, is excited at 254 nm and emits at 300 nm.

Rogan josh ( or roghan josh ) is an aromatic lamb dish of Persian origin, which is one of the signature recipes of Kashmiri cuisine.

In the context of organic molecules, aryl refers to any functional group or substituent derived from an aromatic ring, be it phenyl, naphthyl, thienyl, indolyl, etc.

* Ar for any aromatic substituent

While it is known that there must be an aromatic system at the fifth position of the pyrazole, optimizing this substituent is difficult since it is not known what combination of modifications will provide the highest potency and selectivity due to the flexible nature of the 5-aryl system.

The halogen dance rearrangement is an organic reaction in which a halogen substituent moves to a new position on an aromatic ring system.

Yet as an aromatic substituent the thio group is less effective as an activating group than the alkoxy group.

The residue from the distillation of high-temperature coal tar, primarily a complex mixture of three or more membered condensed ring aromatic hydrocarbons, was listed on 28 October 2008 as a substance of very high concern by the European Chemicals Agency.

* Oxidase test on nutrient agar tests for the production of the enzyme oxidase, which reacts with an aromatic amine to produce a purple color.

Archibald Scott Couper in 1858 and Joseph Loschmidt in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but the study of aromatic compounds was in its earliest years, and too little evidence was then available to help chemists decide on any particular structure.

Mastic ( aromatic, ivory coloured resin ) is grown on the Aegean island of Chios.

The principle can easily be extended over larger aromatic molecules like naphthalene, anthracene, ovalene, and so on, and, if the process is taken to its extreme, graphene.

Traditionally, many U. S. blends are made of American Burley with sweeteners and flavorings added to create an " aromatic " flavor, whereas " English " blends are based on natural Virginia tobaccos enhanced with Oriental and other natural tobaccos.

For a second ring, the label will be 2 ( naphthalene: c1cccc2c1cccc2 ( note the lower case for aromatic compounds )), and so on.

Blending elements of several Southeast Asian traditions, Thai cooking places emphasis on lightly prepared dishes with strong aromatic components.

Today, Austrian Chardonnays range from the rich, oaked aged varieties to leaner, more aromatic styles based on Austrian Rieslings to sweet late harvest styles.

The famous Hückel 4n + 2 rule for determining whether ring molecules composed of C = C bonds would show aromatic properties was first stated clearly by Doering in a 1951 article on tropolone.

Hence, the fraction of X-Pro peptide bonds in the cis isomer under unstrained conditions ranges from 10-40 %; the fraction depends slightly on the preceding amino acid, with aromatic residues favoring the cis isomer slightly.

strain R1 has been shown to grow on a variety of aromatic compounds, including homocyclic compounds, such as hydroxybenzoates, as well as N-heterocycles, including pyridine and picoline.

The position of these chemical shifts is influenced by aromatic ring current, and these values may change depending on substituents.

The popular aromatic Angostura bitters lists Gentian as fourth on its ingredients list.

Pistacia lentiscus () ( Mastic ) is a dioecious evergreen shrub or small tree of the Pistacio genus growing up to tall which is cultivated for its aromatic resin, mainly on the Greek island of Chios.

Most species are trees or shrubs, a few are herbs ( Boenninghausenia ), frequently aromatic with glands on the leaves, sometimes with thorns.

Pellucid glands, a type of oil containing cavities, are found on the leaves responsible for the aromatic smell of the family's members ; traditionally they have been the primary synapomorphic characteristic to identify the Rutaceae.

The intensity and longevity of a perfume is based on the concentration, intensity and longevity of the aromatic compounds ( natural essential oils / perfume oils ) used: As the percentage of aromatic compounds increases, so does the intensity and longevity of the scent created.

Nordmann Fir, Noble Fir, Fraser Fir and Balsam Fir are popular Christmas trees, generally considered to be the best for this purpose, with aromatic foliage that does not shed many needles on drying out.

Several tests for organic material have been performed on the meteorite and amino acids and polycyclic aromatic hydrocarbons ( PAH ) have been found.

The smell ( and therefore the taste ) of coffee depends heavily on the oils containing aromatic compounds that are dissolved out of the beans during the brewing process.

* aromatic oils, based on aromatic hydrocarbons ( distinct from essential oils )