Aromatic Resonance – What It Is and What It Is Not

[caption id="attachment_19938" align="alignright" width="440"] Prominent resonance structures.[/caption] Sometimes a chemistry or physics concept is misunderstood even by the reader of above-average intelligence and education. Such is the case with the chemist’s use of the term aromatic resonance. There are a small number of recognized rules for aromatic behavior. These include: cyclic geometery planarity 4n + 2 contributing, de-localized, conjugated (π) double bonds An Example of What Aromatic Resonance Is Not The best and oldest known example is benzene, C₆H₆. Benzene is cyclic (one ring), planar (flat), and has 6 delocalized, conjugated double bonds. Frequently, the organic chemist simply renders benzene’s structure… There is a carbon atom at each vertex of the hexagonal ring. Attached to each carbon and pointing outward from it is one hydrogen atom. Now each carbon atom…
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Transition from Ice to Water to Vapor

[caption id="attachment_5490" align="alignright" width="440"] Hydrogen Bonding - CCA SA 3.0 Unported by Magasjukur2[/caption] The transition from ice to water to steam. What happens? A block of ice has a temperature well below freezing and is warmed gradually. It reaches above the boiling point. What transitions occur along the way? What are the processes? Transition: Solid to Liquid At first, the heat supplied simply increases the temperature of the ice. The temperature of the surface is somewhat warmer than the ice inside. It takes time for heat to penetrate. Eventually, the outer layer of the ice reaches the melting point. The outside ice melts first—then the inner ice. [caption id="attachment_5491" align="alignleft" width="220"] Melting Ice[/caption] During melting, the heat energy is spent breaking the stiff hydrogen bonds. None of it is spent…
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