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In organic and physical organic chemistry, Clar's rule is an empirical rule that relates the chemical stability of a molecule to its aromaticity.It was introduced in 1972 by the Austrian organic chemist Erich Clar in his book The Aromatic Sextet.
The first, which was proposed by Kekulé in 1865, later proved to be closest to the true structure of benzene. This structure inspired several others to draw structures that were consistent with benzene's empirical formula; for example, Ladenburg proposed prismane, Dewar proposed Dewar benzene, and Koerner and Claus proposed Claus' benzene ...
Two different resonance forms of benzene (top) combine to produce an average structure (bottom). 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.
In benzene, however, 23.4 kJ (5.6 kcal) are needed to hydrogenate one mole of double bonds. The difference, being 143.1 kJ (34.2 kcal), is the empirical resonance energy of benzene. Because 1,3-cyclohexadiene also has a small delocalization energy (7.6 kJ or 1.8 kcal/mol) the net resonance energy, relative to the localized cyclohexatriene, is a ...
Stability: Stable, but very flammable Melting point: 5.5 C Water solubility: negligible Specific gravity: 0.87 Principal hazards *** Benzene is a carcinogen (cancer-causing agent). *** Very flammable. The pure material, and any solutions containing it, constitute a fire risk. Safe handling
Diagram showing the ortho, meta and para positions relative to a substituent X on a benzene ring. Electron donating groups are typically divided into three levels of activating ability (The "extreme" category can be seen as "strong".) Electron withdrawing groups are assigned to similar groupings.
In the following keto-enol tautomerization, the product enol is more stable than the original ketone even though the ketone contains an aromatic benzene moiety (blue). However, there is also an antiaromatic lactone moiety (green). The relief of antiaromatic destabilization provides a driving force that outweighs even the loss of an aromatic ...
7), which is protonated benzene. Two hydrogen atoms bonded to one carbon lie in a plane perpendicular to the benzene ring. [ 4 ] The arenium ion is no longer an aromatic species; however it is relatively stable due to delocalization: the positive charge is delocalized over 3 carbon atoms by the pi system , as depicted on the following resonance ...