aromatic Archives - Quirky Science

10May 2019 by Vincent Summers No Comments

Motor Oil Degradation in Automotive Engines

Why is it so important to change the motor oil in your car? The answer is due to motor oil degradation. Unrecycled motor oils originate from naturally occurring crude oil. As such, motor oils are necessarily a complex combination of organic compounds: Molecules made simply of carbon and hydrogen. A percentage of these hydrocarbons include ring structures—whether saturated aliphatic rings or aromatic rings (benzene or polycyclic). However, the largest percentage of motor engine oil consists of straight and branched chain hydrocarbons of varying lengths. Motor oils are high-quality lubricants, but even the best of these products will degrade with use. Why is Oil a Lubricant? A good lubricant must readily flow and have sufficient viscosity. It should not freeze in even cold environments. It should possess a high level of…

13Feb 2018 by Vincent Summers No Comments

Is Cyclopropenethione Aromatic, As Is Its Oxygen Analog?

Chemistry, Logic

As small as it is, and even with a heteroatom in its make up, cyclopropenethione is aromatic, in the same way cyclopropenone is aromatic. Its aromaticity is not due to a theoretically electrically neutral structure, as in Figure 1, but to its "alternative" zwitterionic structure, shown in Figure 2. Aromatic Characteristics Hückel descriptors fall short of aromaticity if cyclopropenethione exhibited only the structure drawn in Figure 1. In addition to a closed and flat ring, aromaticity requires a 4n+2 number of π-electrons (pi), where n is usually a small integer. In the un-ionized form of Figure 1, each carbon atom has a π-electron, for a total of 3 electrons. This is because every double bond consists of one π-electron plus one σ-electron (sigma) per constituent atom. Widening Perspectives: Cyclopropenethione The…

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…

24May 2016 by Vincent Summers No Comments

Why Cyclodecapentaene is Not an Aromatic Hydrocarbon

Chemistry

[caption id="attachment_16073" align="alignright" width="440"] Fig 1. Cyclodecapentaene - all cis form.[/caption] There are aromatic hydrocarbons and there are non-aromatic hydrocarbons. For basic mono-ring structures that have alternating carbon-carbon double bonds, there is a rule called Hückel’s rule that defines whether a given hydrocarbon can be aromatic or not. It might seem, at first that cyclodecapentaene (C10H10 or [10]-annulene) should be aromatic. Yet, cyclodecapentaene is not an aromatic hydrocarbon. Let’s find out why not. A Few Simple Rules for Aromatic Behavior The double bonds in the ring must be conjugated (alternating). This allows for the electrons to be delocalized [in conceptualization be flipped in either a clockwise or counterclockwise direction]. This allows for the presence of what is called a ring current. The ring must be flat. The mono-ring must feature…

16May 2016 by Vincent Summers 1 Comment

Azulene or Cycloheptatrienyl Cation Cyclopentadienyl Anion “Salt”?

Chemistry, Education

[caption id="attachment_14421" align="alignright" width="440"] The dipolar azulene hydrocarbon[/caption] Azulene is a fascinating hydrocarbon. It is bicyclic, meaning it has a kind of double ring structure. It is a seven-member ring adjoined to a five-member ring by a shared two-carbon wall. One ring resembles cycloheptatriene. The other ring, cyclopentadiene. And yet, there is something different about azulene. Or should we say some things different? Unusual Qualities Although azulene is a hydrocarbon, it is a deep blue hydrocarbon, something very much out of the ordinary. The Lactarius indigo mushroom, in fact, gets its blue coloration from a derivative of azulene. In addition, although most plain hydrocarbons have little or no dipole moment, azulene has a dipole moment of 1.08 Debye units. This is equal to that of the nitrogen-containing diphenylamine molecule. [caption…

16May 2016 by Vincent Summers No Comments

Cyclobutadiene Antiaromatic or Other Destabilization Factors?

Chemistry

Clearly cyclobutadiene is not aromatic. Is cyclobutadiene antiaromatic? Or is its lack of stability due to other factors? Cyclobutadiene is a four-carbon hydrocarbon. The –diene part of its name indicates it has two double bonds. The cyclo– part indicates it is not a chain structure, but a cyclic (ring) structure. Now double bonds hold atoms tighter than single ones do. So they are shorter than single bonds. This causes cyclobutadiene to assume a rectangular shape. If it were square instead, it would indicate the four carbon to carbon bonds were identical, and aromatic. Cyclobutadiene's four hydrogen atoms point away from the ring. Analyzing the Structure Cyclobutadiene is flat. The two double bonds of cyclobutadiene are conjugated. That is, their ring structure alternates double bond, single bond, double bond, single bond.…

13May 2016 by Vincent Summers 4 Comments

Is Cyclopropenone Aromatic or Not?

Chemistry

Is cyclopropenone aromatic? Before reading on, try to anticipate the answer to that question. When most students think of aromatic, they think of simple hydrocarbons—compounds composed of hydrogen and carbon atoms only. The best known example of an aromatic hydrocarbon is the 6-sided cyclic compound benzene—C₆H₆. Benzene, if drawn according to classical structures, has alternating single and double bonds between carbon atoms. Basic Qualifications for Aromaticity A double bond consists of one sigma (σ) and one pi (π) bond. If the ring is single rather than multiple (as, for instance, for naphthalene, which is comprised of two fused rings), and if it has 4n+2 completely conjugated π electrons in a closed loop or ring, is neutral, and is flat, the structure obeys Hückel’s rule and will be aromatic. There are…

14Mar 2016 by Vincent Summers No Comments

Imidazole Synthesis and Chemistry

Biology, Chemistry

Imidazole is an aromatic 5-member ring organic compound containing two skeletal atoms other than carbon. Both of those are nitrogen. One of the molecule's resonance structures, if it actually existed, would contain a secondary amine group (-NH-), an imine group (=N-), and an alkene group (-C=C-). The other resonance structure would contain two imine groups and a methylene group (-CH₂-). Those structures are drawn below. However, imidazole doesn't act like either of them. This is typical for aromatic compounds. We will briefly discuss the ring's synthesis and chemistry. Synthesis Imidazole is formed by reacting glyoxal with formaldehyde in the presence of ammonium acetate in acetic acid. The driving energy is microwave radiation. More generally, this reaction is used to produce substituted imidazoles. The basic reaction, however, is written, OHC-CHO +…

07May 2014 by Vincent Summers No Comments

The Iron Sandwich Compound Ferrocene

Chemistry

[caption id="attachment_6151" align="alignright" width="440"] Ferrocene - an Iron Sandwich Compound[/caption] Who doesn't love a ham and cheese sandwich? Or a peanut butter and jelly sandwich? Well, there are special chemical substances that resemble sandwiches. There is, for example, the sandwich compound ferrocene, (C₅H₅)₂Fe. It consists of an atom of iron "sandwiched" between two cyclopentadiene molecules. Sandwich Compound The classification of such metallic organic compounds is metallocene. D-orbital electrons in the iron atom add to the pi-electrons of two cyclopentadiene molecules. This stabilizes the structure, since the cyclopentadienyl anion (-1 charge) has aromatic properties. The iron atom adopts, in effect, a ferrous (+2) electrical charge. Other Metallocenes In general, metallocenes have mostly been of laboratory interest. Some do exhibit a marked level of importance. One application is in catalysis. Other metallocenes…

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.…