Welcome to Wikipedia
Download 190.74 Kb.
|
- Navigate this page:
- References[edit]
- Bibliography[edit]
- Contents
- Benzene ring model[edit]
See also[edit]
References[edit]
Bibliography[edit]
External links[edit]Aromatic hydrocarbonFrom Wikipedia, the free encyclopedia Jump to: navigation, search "Arene" redirects here. For other uses, see Arene (disambiguation). An aromatic hydrocarbon or arene[1] (or sometimes aryl hydrocarbon)[2] is a hydrocarbon with alternating double and single bonds between carbon atoms forming rings. The term 'aromatic' was assigned before the physical mechanism determining aromaticity was discovered; the term was coined as such simply because many of the compounds have a sweet or pleasant odor. The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible such hydrocarbon, benzene. Aromatic hydrocarbons can be monocyclic (MAH) or polycyclic (PAH). Some non-benzene-based compounds called heteroarenes, which follow Hückel's rule (for monocyclic rings: when the number of its π-electrons equals 4n+2), are also called as aromatic compounds. In these compounds, at least one carbon atom is replaced by one of the heteroatoms oxygen, nitrogen, or sulfur. 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.[3]
Benzene ring model[edit]
Benzene
Main article: aromaticity Benzene, C6H6, is the simplest aromatic hydrocarbon, and it was the first one recognized. 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 each to the two neighboring carbons. This leaves one to share with one of its two neighboring carbon atoms, which is why the benzene molecule is drawn with alternating single and double bonds around the hexagon. The structure is also illustrated as a circle around the inside of the ring to show six electrons floating around in delocalized molecular orbitals the size of the ring itself. This also represents the equivalent nature of the six carbon-carbon bonds all of bond order ~1.5. This equivalency is well explained by resonance forms. The electrons are visualized as floating above and below the ring with the electromagnetic fields they generate acting to keep the ring flat. General properties:
The circle symbol for aromaticity was introduced by Sir Robert Robinson and his student James Armit in 1925[4] and popularized starting in 1959 by the Morrison & Boyd textbook on organic chemistry. The proper use of the symbol is debated; it is used to describe any cyclic pi system in some publications, or only those pi systems that obey Hückel's rule on others. Jensen[5] argues that in line with Robinson's original proposal, the use of the circle symbol should be limited to monocyclic 6 pi-electron systems. In this way the circle symbol for a 6c–6e bond can be compared to the Y symbol for a 3c–2e bond. Directory: uploads uploads -> 587 Return function, r i(X) r i(0) r i(1) r i(2) r i(3) 1 0 2 4 6 Thermal Station, I 2 0 1 5 6 3 0 3 5 6 10 uploads -> Department of science and humanities department of mathematics part-a questions and answers uploads -> The Case Against the nypd’s Quota-Driven ‘Broken Windows’ Policing What Is It? uploads -> For want of a nail uploads -> Ownership Models There are two different types of ownership models uploads -> Police Militarization uploads -> City of rising star regular meting thursday, july 14, 2016 uploads -> Township of winfield uploads -> Stop Militarizing Law Enforcement Act of 2014 uploads -> The Black Panther Party’s Ten-Point Program What We Want Now! Download 190.74 Kb. Share with your friends:
|