Chemistry Archives - Page 17 of 22

20May 2015 by Vincent Summers 1 Comment

The Persistent Triphenylmethyl Free Radical

Chemistry

[caption id="attachment_19350" align="alignright" width="440"] Three phenyl groups plus an unpaired electron are bonded to a central carbon.[/caption] The persistent triphenylmethyl free radical. What is it? What is a free radical and how, and in what sense, is this one "persistent"? The term free radical is a household word, due to its association with food and with body health. Although the expression is bandied about, the public at large does not know what it means. It relates to the concept of atoms, molecules, and electrons. A chemical free radical is defined as a molecule having no net electrical charge, that nevertheless, has at least one unpaired valence electron. Do you find this definition hard to follow? Continue reading and view the hyperlinked graphic model, cited in the following paragraph. [sc name="MidArticleAdsense"]…

27Nov 2014 by Vincent Summers No Comments

LCAO MO Chemical Bonding Theory and Examples

Chemistry

[caption id="attachment_8903" align="alignright" width="440"] Antibonding sigma orbital.[/caption] LCAO MO The nature of the chemical bond has been of interest for hundreds of years. Theories have been developed to explain how atoms combine to form molecules. The most successful theory to date is the (L)inear (C)ombination of (A)tomic (O)rbitals - (M)olecular (O)rbitals or LCAO MO bonding theory. You've got it: yet another acronym. Atoms have nuclei. These contain protons and neutrons. Electrons travel around these nuclei. Orbitals are mathematical functions that describe their trajectories. As atoms form molecules, atomic orbitals combine to form molecular orbitals. Since orbital functions are described by the Schrödinger wave equation and that equation is linear, molecular orbitals can be described by the linear additive combining of atomic orbitals. Example of Hydrogen Ordinary hydrogen has one proton,…

26Nov 2014 by Vincent Summers 1 Comment

Yeast and Baking Powder Bread Dough

Chemistry, Food

[caption id="attachment_6469" align="alignright" width="440"] CC-SA 3.0 by Lou Sander[/caption] Have you ever made dough with yeast and baking powder? Bread is one of the staples of life. Some translations of the Bible read, "Give us this day our daily bread." Most bread is leavened bread. Leavening refers to an ingredient or ingredients designed to raise and lighten bread, through the incorporation of tiny gas bubbles throughout the dough. Dough rises through two mechanisms, employing yeast and baking powder. The first is a biological process, the second is a chemical process. Either procedure results in a delicious, decidedly edible product. Yeast Rolls Yeast rolls and other breads are raised by means of microscopic animals called yeast. Yeast combines oxygen from the air with carbohydrates such as glucose sugar to produce carbon…

21Nov 2014 by Vincent Summers No Comments

Esters: Their Structure and Preparation

Chemistry

Many esters may be directly prepared by reacting an alcohol with an organic acid.1 To better understand what an ester is, it is important to understand why carbon is so special. Carbon Bonds to Itself Frequently, inorganic compounds are relatively small structures. For instance, barium metal, Ba, reacts readily with chlorine gas, Cl2, to give barium chloride, BaCl2. Ba + Cl2 → BaCl2 Notice barium atoms do not join to each other to form a chain, ring, or some other complex structure. However, carbon – the main element of organic compounds – can and often does bond to itself, forming larger molecules. For instance, diethyl ether is written, H3C-CH2-O-CH2-CH3 Two of the carbon atoms on the left are bonded to one another, as are the two on the right. In fact, chains and…

17Nov 2014 by Vincent Summers No Comments

Keto Enol Tautomerism

Chemistry

Is the term keto enol tautomerism familiar to you? If not, give attention to the ensuing discussion. Organic chemistry would be of no value if not for multiple bonds and functional groups. Such groups impart the reactivity needed to sustain life. One attachment is carbonyl (–C=O). Tautomerism Given the right environment, atoms of a carbonyl group tautomerize. That is, they can exchange a proton (hydrogen). In so doing a π-bond is formed or disappears. The carbonyl or keto form assumes the alkene-alcohol or enol form, or vice versa. For acetone, the two forms are, CH3–(C=O)–CH3 keto form CH2=C(OH)–CH3 enol form See the image above. [sc name="MidArticleAdsense"] Both Aldehydes and Ketones Participate A ketone has its carbonyl carbon atom linked to two other carbon atoms. An aldehyde has its carbonyl carbon…

16Nov 2014 by Vincent Summers 1 Comment

The Zwitterion – Nature, Occurrence, Ongoing Research

Chemistry

What in the world is a zwitterion? What is its importance? Molecules are bonded atoms that act as a unit. They are electrically balanced. This means they contain a total number of electrons equal to the number of protons. If a chemical structure does not possess an equal number of electrons and protons it is an ion. Molecules as a unit are electrically neutral. However, there may be local charges due to geometry or electronegativity. These charges are mostly less than that of a proton or electron. There is an exception. It is the zwitterion. This kind of ion has a full positive and a full negative charge. In organic chemistry there may be an alkyl backbone consisting of carbon (C) and hydrogen (H). Other groups (pendant groups) include hydroxyl,…

16Nov 2014 by Vincent Summers 1 Comment

Organic Chemistry: What is Ring Strain?

Chemistry

[caption id="attachment_16313" align="alignright" width="440"] Cyclopropane suffers from ring strain.[/caption] Carbon ring strain? What is that? Let's begin at the beginning. The element carbon is one of a small number of elements that can bond to itself repeatedly. Compare gases such as oxygen (O2), called diatomic gases because generally only two atoms unite. Oxygen is exceptional in that it does form the triatomic molecule, ozone (O3). However, carbon can form even lengthy chains. Thus, carbon can form, not only methane (CH4), but ethane (H3C-CH3), propane (H3C-CH2-CH3), butane (H3C-CH2-CH2-CH3), pentane (H3C-CH2-CH2-CH2-CH3), and so on. Curiously, carbon can also close those chains to form rings, much as a woman can close a string of pearls about her neck using a clasp. [sc name="MidArticleAdsense"] Cyclization Although methane cannot so close, nor can ethane, the…

16Nov 2014 by Vincent Summers No Comments

Organic Chemistry: What is a Lactam?

Chemistry

Most have never heard of a lactam. What is it? How can it be produced? Compounds are chemicals formed by combining two or more different atoms, the basic building blocks of matter. Organic compounds contain carbon, frequently bonded to itself, whether in chains, rings, or some other geometric structure. There are so many organic compounds, they must be categorized according to "functional groups." Functional groups are specialized structures within a compound that may contain a special atom, such as nitrogen, sulfur, phosphorous, etc. One kind of compound categorized by functional group is an amide. An amide results when an organic acid group reacts with a nitrogen-containing amine group and loses water. A lactam is a special kind of amide. It may serve as an intermediate in forming heterocyclic rings. Inorganic…

16Nov 2014 by Vincent Summers No Comments

Terpenes and Terpenoids: Isoprene Rule

Chemistry

There are thousands of chemical compounds in nature. They are divvied up into categories or classifications. These include hormones, alkaloids, vitamins, neurotransmitters, enzymes, proteins, and nucleic acids. One group of chemicals follows a structure rule called the isoprene rule. Many every day substances are part of this group. One example is turpentine. Another is beta-carotene (the source of the orange color in carrots). Chemicals such as these derived from isoprene are called terpenoids. Structure and Statement of the Isoprene Rule Isoprene consists of carbon and hydrogen. But it is not limited to single bonds. See the image of isoprene (C5H8) featured with this article. The double lines stand for double bonds. Since the carbon pairs involved have two bonds rather than one, a hydrogen atom is missing from each of them.…

14Nov 2014 by Vincent Summers 3 Comments

Hydrogen Metal?

Chemistry

We're familiar with hydrogen as a gas, but hydrogen metal? Could it be that's what hydrogen is? [Artist's conception at right.] There are more than 100 substances listed in the Periodic Table of the Elements. This table is called "periodic" because, although each column is completely different, the properties of one row are very similar to the properties of the next. If you start on the left with an alkali metal, and you go through a row, you go to the next row and another alkali metal. An Anomaly Most of the alkali metals, such as lithium, sodium, and potassium, are very similar. They are soft, reactive, silvery solids. They have one outer electron and conduct electricity. They are easily cut with a knife. But, there is an exception –…