26Apr 2017 by Vincent Summers 2 Comments

Benzene from Coal and Lye?

Chemistry, Education
[caption id="attachment_17736" align="alignright" width="480"] Coal and Lye[/caption] As a youth, I read whatever chemistry books I could get hold of. One made reference to an obscure synthesis of the liquid aromatic compound benzene from coal and lye, by means of heat. This reaction would seem to be an improbable one. Can a stoichiometric equation be written for such a synthesis? The answer is, Yes. This in itself does not guarantee the reaction can actually take place. 6 NaOH + 9 C → 3 Na2O + C6H6 + 3 CO I learned of this synthesis from an old book, possibly published in the 1800s. Coal and Lye - What Conditions? Such a reaction strongly suggests isolation. The reaction required considerable heat. Also, air was to be excluded, since carbon would react…
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07Nov 2016 by Vincent Summers 4 Comments

Aromatic Resonance – What It Is and What It Is Not

Chemistry
[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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11Sep 2015 by Vincent Summers No Comments

Do Double Bonds Flip? Does Electron Density Move?

Chemistry
[caption id="attachment_7788" align="alignright" width="440"] 1,3,5 Hexatriene - NIST Image[/caption] How do double bonds flip, and what is the significance? The shorthand drawing of a double bond looks like an equal sign between two atoms. The double bond between the two carbon atoms of ethene gas, H₂C=CH₂, well illustrates this. Some organic compounds possess conjugated (alternating) double bonds. A simple example of this is 1,3,5-hexatriene. [caption id="attachment_7785" align="alignright" width="340"] Fig. 1. 1,3,5 Cyclohexatriene.[/caption] What If? But what if the ends of that 1,3,5 hexatriene are joined, with the loss of two hydrogen atoms, to make a ring one might be tempted to call 1,3,5-cyclohexatriene? In fact, such a molecule, if flipped left-to-right, is seen to be identical with 2,4,6-cyclohexatriene! The numbers can be dropped and the molecule can simply be named…
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23Mar 2014 by Vincent Summers No Comments

The Quintessential Aromatic Hydrocarbon Benzene (Pt.3)

Chemistry
[caption id="attachment_18860" align="alignright" width="440"] Figure 1.[/caption] The aromatic hydrocarbon benzene, chemical formula C6H6, is the single most-often discussed of the aromatic hydrocarbons. It possesses the quintessential aromatic structure. How is that? It possesses the Hückel Rule correct number of 4n + 2 number π-electrons, for n = 1, and is flat. In addition, it meets all the other requirements for aromatic compounds. As an aromatic compound, its chemistry is considerably different than it would be if it existed as a mere cyclohexatriene isomer. We will discuss those differences in this, the third installment of our three-part article. Behavior of Hypothetical Cyclohexatriene Since cyclohexatriene would behave as if it were merely three conjugated1 double bonds, we would expect the compound to behave as any other alkene—rich in available electrons—only more so.…
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23Mar 2014 by Vincent Summers No Comments

The Quintessential Aromatic Hydrocarbon Benzene (Pt.2)

Chemistry
[caption id="attachment_6069" align="alignright" width="440"] Benzene De-localized Pi-system - CCA Share Alike 3.0 Unported by Vladsinger[/caption] In Part One of The Quintessential Aromatic Hydrocarbon Benzene, we saw that the so-called 1,3,5-cyclohexatriene was really not completely described by the structure that that name implies. It is equivalent to 2,4,6-cyclohexatriene (if you flip the 1,3,5- structure over, and you get the 2,4,6- structure), and includes a variety of other contributing factors. Although we did not list them, they may include ionic contributors.1 In general, these are discounted. Visualizing Benzene's Structure The conclusion is that the compound actually has six equivalent bonds between adjacent carbon atoms, forming six internal angles angle each equal to 60°. The bonds are each, then, “single-and-one-half” bonds between each carbon pair. The molecule is flat, even as a collection…
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23Mar 2014 by Vincent Summers No Comments

The Quintessential Aromatic Hydrocarbon Benzene (Pt.1)

Chemistry
[caption id="attachment_14959" align="alignright" width="440"] Cyclohexane - Chair Form[/caption] Benzene? What's that? Living creatures universally share an important characteristic: they all are constructed of carbon-containing compounds. For that reason, chemists call such compounds organic. Now the term organic has taken on additional meaning. Compounds that are similar, but not found in nature, are also called organic compounds. One group of organic compounds, whether found in nature or not, possess special properties—chemical and physical—that put them into a category apart. Once it was thought such compounds were distinguishable by smell or aroma. Each was labeled an aromatic, and—the property itself—aromaticity. Simple Hydrocarbons The simplest hydrocarbon1 is methane (CH4)—a gas. It possesses a tetrahedral structure, with a carbon atom at its center and four hydrogen atoms at the corners (See Figure 1). Since…
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