Chemistry Archives - Page 2 of 22

11Aug 2019 by Vincent Summers 2 Comments

Tetrahydrofuran or Diethyl Ether – Which to Use?

Chemistry

Tetrahydrofuran (C4H8O) is a heterocyclic hydrocarbon. One of the carbon atoms of a cyclopentane ring (along with its two hydrogen atoms) is replaced by an atom of oxygen. THF is an ether. It's frequently used for its solvent properties. In certain organometallic reactions, tetrahydrofuran replaces all or part of the standard solvent diethyl ether, (C2H5-O-C2H5), written in chemists' shorthand Et-O-Et. Tetrahydrofuran Vs. Diethyl Ether Although THF is essentially diethyl ether gone cyclic, its physical properties differ somewhat. A prime example of that relates to hydrogen bonding. Although both molecules possess an electron-rich oxygen atom, in THF, the oxygen is openly exposed. The ring can twist, but that's about it. The hydrocarbon portions of ethyl ether¹ have much greater freedom of motion. They can sweep around, making hydrogen bonding easier to…

10Aug 2019 by Vincent Summers 1 Comment

Organic Ozonides – How They Form, How They React

Chemistry

As you might guess, organic ozonides may be derived from ozone. So let's first consider the nature of ozone. The ozone molecule, O3 is bent and unstable. It is polarized and is quick to react with unsaturated molecules, notably alkenes and alkynes. The image provided illustrates the result. What, however, is the mechanism producing the result in a typical case?¹ Initially, all three oxygen molecules add to the alkene on the same side of what was previously a double bond. This structure, however, is a transient intermediate, which rearranges to form the ozonide structure. Ozonides are relatively stable. However, they can be readily split to yield a pair of carbonyl compounds. Organic Ozonides in Synthesis Some ozonides are explosive, so they are seldom isolated. However, ozonides can be made to…

01Aug 2019 by Vincent Summers 1 Comment

Don’t Monkey Around – What is a Banana Bond?

Chemistry, Education

A banana bond is not a typical chemical bond by any stretch of the imagination. It is a 3-center, 2-electron bond. The shape of this kind of bond resembles a banana, hence its name. Perhaps the simplest example of a banana bond is demonstrated between boron and hydrogen in the diborane molecule, B2H6. Elemental Atomic Orbitals We begin with a discussion of the much simpler, more typical 2-center, 2-electron single bond. When atoms form molecules, the atomic orbitals involved transform into molecular orbitals. Let's consider a very simple example. Say we want to form one C-H bond of the molecule methane (CH4). Now hydrogen atoms only have one electron. The single electron lies in the 1s2 orbital. That type of orbital possesses spherical symmetry. Unlike hydrogen, carbon has 12 electrons…

27Jul 2019 by Vincent Summers No Comments

The Curiously Stable Dodecaborate Dianion

Chemistry

There is a lot of talk concerning the chemistry of carbon. And this is totally appropriate. The chemistry of carbon is the chemistry of life. But little is known about boron, which is right next door to carbon on the periodic table of the elements. Yet, boron is a most interesting element. For one thing, boron, like carbon, is capable of bonding to itself. Boron Bonds to Itself There are many compounds in which the element does just that, it bonds to itself. Consider a few of its combinations with hydrogen (see the image). As you advance to larger boron-hydrogen structures, however, it becomes clear the molecular bonding for boron differs considerably from the hydrocarbons. Dodecaborane Dodecaborane somewhat resembles dodecahedrane (C20H20) in outward appearance, even though in terms of bonding,…

25Jul 2019 by Vincent Summers No Comments

Ozone – The Other Oxygen: A Brief Discussion

Chemistry, Physics

Ozone (O3), a triatomic form of the ordinarily diatomic oxygen (O2), is a curious species. We will discuss some of ozone's curious physical properties. We will not include information related to health or the environment. Molecular Bonding Just as it takes two points to determine a straight line, diatomic oxygen is also linear. It's bond length is 1.208 Å (equal to 120.8 pm). Ozone is not linear; it is bent at an angle of 116.8o, which is greater than the measure of the angle for a water molecule, 104.5o. Comparing Boiling Points The third oxygen atom plus the relatively large angle suggests ozone should boil at a higher temperature than oxygen. In fact, this is the case. This is because the bent ozone molecules, as seen in the illustration, produces…

22Jul 2019 by Vincent Summers No Comments

Chemistry: What’s a Chromophore?

Chemistry

One online definition of chromophore is "an atom or group whose presence is responsible for the color of a compound." Although one may think of a chromophore that includes a metal atom such as copper, nickel, or cobalt, in organic chemistry a chromophore is more likely to consist of a collection of carbon-carbon multiple bonds, perhaps with modifying features. It is the organic variety we discuss in this article. Multiple Bonds Most organic compounds incorporate one or more of three carbon-to-carbon bond varieties: single bonds, double bonds, triple bonds. When drawing a basic organic compound, these are usually represented by: C–C, C=C, and C≡C, respectively. Although such notations are quite useful, they afford little information concerning bond nature and behavior. Bond Hybridization The best working hypothesis for bonding between atoms…

20Jul 2019 by Vincent Summers No Comments

Why Some Sugars Have a Cyclic and a Chain Structure

Chemistry, Education

In your current course of organic chemistry, you're studying sugars. You notice in a text or see on the web a particular sugar, you've searched for by name. What is its true structure? You see it drawn as a chain structure with pendant groups. As you read about it, you see reference to another structure... a cyclic structure! What gives? Sugars: Example Fructose Some chemicals undergo change with the most minimal modification of environment. One example is keto-enol tautomerism. Fructose and certain other sugars experience something similar. It reacts reversibly, to form two cyclic hemiketals. Fructose Hemiketals A hemiketal forms by combination of an alcohol group with a ketone group. Fructose supplies both reactive groups, internally. For the generic reaction for hemiketal formation, see the accompanying illustration. Note the presence…

15Jul 2019 by Vincent Summers 2 Comments

Carbide Cannons & Miners’ Lamps – The Chemistry?

Chemistry, Technology

When I was a kid, a friend showed me what he called an acetylene cannon. Many know it as a carbide cannon. What made it work? It's all a matter of chemistry. Which Carbide? A carbide is a compound in which carbon is bonded to a more electropositive element. Silicon carbide (SiC) and tungsten carbide (WC) are two well-known examples. What carbide do carbide cannons use? Calcium Carbide The answer is calcium carbide. Lime and coke are placed in an electric furnace. The chemical reaction is: CaO + 3 C → CaC2 + CO2↑ What makes calcium oxide so interesting is its bonding. The valence of calcium is +2. Ordinarily, carbon is assigned a valence of 4. Something's strange here... The puzzle is solved if we write the structure of…

13Jul 2019 by Vincent Summers 1 Comment

Artificial Butter Flavor – Just a Product of the Chem Lab?

Chemistry, Food

You are crunching away at some tasty munchable. Since you're not doing anything else and would like to prove you can do two things at once, you turn the bag/box around and read the ingredients. Yes, yes, oh that! And yes, yes, ah. What's that? Artificial Butter Flavor? What's artificial butter, the product of artificial cows? What Is Artificial Butter Flavor? Simply put, the expression "artificial butter" refers to taste and use, rather than to any single, particular ingredient. A Simple Compound Diacetyl is considered to impart a buttery flavor to foodstuffs. As the illustration shows, diacetyl is a small, simple molecule. Writing it out in full, it is... CH3(CO)(CO)CH3 Note the similarity to two acetic acid (vinegar) molecules... CH3(CO)–OH + HO–(OC)CH3 Synthesis The second image depicts one possible synthetic…

08Jul 2019 by Vincent Summers 1 Comment

Alkene Isomers and Nomenclature: 1,3,5-Hexatriene

Chemistry

Many moons ago, chemistry was divided into two large groups, organic chemistry and inorganic chemistry. Organic chemistry was thought to be the 'chemistry of life'. This was because a mysterious "vital force" associated with life was thought essential to produce organic compounds. Most organic compounds consist of carbon and hydrogen atoms, with or without nitrogen, oxygen, phosphorous, or other atoms. We will discuss a simple hydrocarbon. A hydrocarbon consists solely of carbon and hydrogen. Hydrocarbon Bonds Carbon and hydrogen usually bonds in one of three ways: single bonds (-), double bonds (=), and triple bonds (≡). In this article, we will feature only single and double carbon-to-carbon bonds... two single and three double. The compound is 1,3,5-hexatriene. Notice the featured image (above) that illustrates the most common way it is…