Aromatic hydrocarbons are a class of chemicals that are characterized by having a molecular structure called a benzene ring. The simplest aromatic hydrocarbon is benzene, chemical and hydrocarbon structure is lent its name to the benzene ring. Many toxic aromatic hydrocarbons, and they are unfortunately among the most widespread organic pollutants. Many toxic aromatic hydrocarbons, and they are unfortunately among the most widespread organic pollutants.
Aromatic compounds are derivatives of benzene. simple aromatic compounds, is an aromatic organic compound that consists only of conjugate planar ring structure with the π electron cloud berdelokalisasi. Chemistry is characterized by conjugated double bonds actually in the ring. Aromatic ring heterocyclic compounds can be simple if it contains non-carbon atoms. It may monocyclic such as benzene, naphthalene such bicyclic, or polycyclic like anthracene. Monocyclic aromatic ring is usually a simple five-membered ring, such pirola, or six-membered rings, such as pyridine. All aromatic compounds based on benzene, C6H6 which has six carbon atoms and each corner of the hexagon symbol has a carbon atom bound with hydrogen
Benzene and its derivatives classified in a number of aromatic compounds, is first classification solely based on the flavor of the part of the said compounds. Development of the next stage chemistry chemists realize that the classification should be based on the chemical structure and reactivity, and not on the basis of physical properties. Currently, the term aromatic is retained, but it refers to the fact that all the aromatic compounds of high and stable degree ketidakjenuhannya when dealing with the attacking reagent bonding pi (π).
A. AROMATIC COMPOUNDS
Benzene is a member of a large group of aromatic compounds, ie compounds sufficiently stabilized by pi-electron delocalization. Resonance energy an aromatic compound is helping gained stability.
The easiest way to determine whether a compound is aromatic is to determine the position of the absorption in mspektrum number of protons bound to the atom-atom ring. Proton-bound outward terperisai aromatic rings are very strong and absorbs far down-field than most protons, usually more than 7 ppm.
(Fessenden and Fessenden .454-455: 1982).
Aromaticity is a chemical property in which a conjugated ring bond consists of unsaturated bonds, a couple, or an empty orbit showed stronger stability than the stability of the system consists only of conjugation. Aromaticity can also be considered a manifestation of cyclic delocalization and resonance.
1. A molecule must be cyclic.
2. Each atom in the ring must have π orbital, to form conjugates.
3. Molecules have planar.
4. The number π electrons of the molecule must be odd and satisfy Hückel rule: (4n +2) elektronπ.
B. Aromatic compounds and its structure
Which includes aromatic compounds is
• benzene compounds
• The chemical compound with chemical properties such as benzene
Benzene and benzene derivative compounds first synthesized by Michael Faraday in 1825, from which the gas is used as fuel for lamps penerang.Sepuluh years later it was discovered that benzene has the molecular formula C6H6 thus concluded that benzene has a double bond more than alkenes.
Of the oily residue is buried in the gas mains in London. Currently, the main source of benzene, substituted benzene and aromatic compounds are petroleum: formerly of nearly 90% coal tar compounds active ingredients are aromatic compounds: benzene core has the formula.
a. Structure of Benzene
The double bond in benzene is different from the alkene double bond. The double bond in alkenes can undergo addition reactions, whereas the double bond in benzene can not you get an addition, but benzene can react substitution. Example:
Addition reaction: C2H4 + Cl2 -> C2H4Cl2
Substitution reaction: C6H6 + Cl2 -> C6H5Cl + HCl
Kekulé describe the structure of benzene by carbon atoms linked to one another to form a ring.
Each carbon atom in benzene tying 3 others using sp2 hybridized orbital forming a planar molecule.
Benzene is a symmetrical molecule, hexagonal shape with a bond angle 120o
Each C atom has four orbital into the p orbitals. P orbitals overlap will experience suh (overlapping) to form a cloud of electrons as the source of electrons.
C. AROMATIC COMPOUNDS heterocyclic
According to Erich Hückel, a compound that contains five or six-membered ring is aromatic if:
• all the constituent atoms lie in a flat (planar)
• every atom that form a ring having a 2p orbital
• have the pi electrons in the cyclic arrangement of the 2p orbitals as 4n +2 (n = 0, 1, 2, 3, …)
In addition to benzene and its derivatives, there are several other types of compounds exhibit aromatic properties, which have high unsaturation and showed no reactions like alkenes. Benzene homosiklik included in the class of compounds, ie compounds that have only one type of atom in the ring system. There are heterocyclic compounds, are compounds that have more than one type of atom in the ring system, the ring is composed of one or more atoms that are not carbon atoms. For example, pyridine and pirimidina are aromatic compounds such as benzene. In pyridine one CH unit of benzene is replaced by a nitrogen atom sp2 hybridise, and in pirimidina two CH units replaced by nitrogen atoms are sp2 hybridise.
Membered heterocyclic compounds of five such as furan, thiophene, pyrrole, and imidazole also includes aromatic compounds.
D. TERMS OF AROMATIC COMPOUNDS
1. Molecules have cyclic and flat.
2. have p orbitals perpendicular to the ring plane (pi electron delocalization allow).
3. have p orbitals perpendicular to the ring plane (pi electron delocalization allow)
8 siklooktatetraena not aromatic pi electrons.
(Fessenden and Fessenden .463-464: 1982).
A. Hückel rule
In the year 1931 a German chemist Erich Hückel, suggested that an aromatic compound to be flat, monocyclic (one ring) needs to have as many pi elketron 4N + 2, where n is an integer sebuahn. According to the Hückel rule, a ring with pi electrons as 2,6,10 or 14 can be aromatic, but the ring with 8 or 12 pi electrons, can not be. Siklooktatetraena (with 8 electrons pi) does not comply with Hückel rule for aromaticity.
Aromatic compounds must meet the following criteria:
– Contains a delocalized p electron clouds below and above the plane of the molecule
– Double bonds alternate with single bonds
– Have a total number of 4N +2 p electrons, where n must bulisal numbers: if the number of electrons in a ring of a cyclic p = 12, then n = 2.5 then instead of aromatic compounds