Characterization and classification of organic compounds
Carbon as the element essential to all of life, and hence the basis for a vast field of study. Electronegativity value of fluorine. Plastic polystyrene - important product of the hydrocarbon family. Chemical properties of carboxylic acids and esters.
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There was once a time when chemists thought "organic" referred only to things that were living, and that life was the result of a spiritual "life force." While there is nothing wrong with viewing life as having a spiritual component, spiritual matters are simply outside the realm of science, and to mix up the two is as silly as using mathematics to explain love (or vice versa). In fact, the "life force" has a name: carbon, the common denominator in all living things. Not everything that has carbon is living, nor are all the areas studied in organic chemistry--the branch of chemistry devoted to the study of carbon and its compounds--always concerned with living things. Organic chemistry addresses an array of subjects as vast as the number of possible compounds that can be made by strings of carbon atoms. We can thank organic chemistry for much of what makes life easier in the modern age: fuel for cars, for instance, or the plastics found in many of the products used in an average day.
How it works.
Introduction to Carbon.
As the element essential to all of life, and hence the basis for a vast field of study, carbon is addressed in its own essay. The Carbon essay, in addition to examining the chemical properties of carbon (discussed below), approaches a number of subjects, such as the allotropes of carbon. These include three crystalline forms (graphite, diamond, and buckminsterfullerene), as well as amorphous carbon. In addition, two oxides of carbon--carbon dioxide and carbon monoxide--are important, in the case of the former, to the natural carbon cycle, and in the case of the latter, to industry. Both also pose environmental dangers.
The purpose of this summary of the carbon essay is to provide a hint of the complexities involved with this sixth element on the periodic table, the 14th most abundant element on Earth. In the human body, carbon is second only to oxygen in abundance, and accounts for 18% of the body's mass. Capable of combining in seemingly endless ways, carbon, along with hydrogen, is at the center of huge families of compounds. These are the hydrocarbons, present in deposits of fossil fuels: natural gas, petroleum, and coal.
A propensity for limitless bonding.
Carbon has a valence electron configuration of 2s22p2. Likewise all the members of Group 4 on the periodic table (Group 14 in the IUPAC version of the table)--sometimes known as the "carbon family"--have configurations of ns2np2, where n is the number of the period or row the element occupies on the table. There are two elements noted for their ability to form long strings of atoms and seemingly endless varieties of molecules: one is carbon, and the other is silicon, directly below it on the periodic table.
Just as carbon is at the center of a vast network of organic compounds, silicon holds the same function in the inorganic realm. It is found in virtually all types of rocks, except the calcium carbonates--which, as their name implies, contain carbon. In terms of known elemental mass, silicon is second only to oxygen in abundance on Earth. Silicon atoms are about one and a half times as large as those of carbon; thus not even silicon can compete with carbon's ability to form an almost limitless array of molecules in various shapes and sizes, and with various chemical properties.
Carbon is further distinguished by its high value of electronegativity, the relative ability of an atom to attract valence electrons. To mention a few basic aspects of chemical bonding, developed at considerably greater length in the Chemical Bonding essay, if two atoms have an electric charge and thus are ions, they form strong ionic bonds. Ionic bonding occurs when a metal bonds with a nonmetal. The other principal type of bond is a covalent bond, in which two uncharged atoms share eight valence electrons. If the electronegativity values of the two elements involved are equal, then they share the electrons equally; but if one element has a higher electronegativity value, the electrons will be more drawn to that element.
The electronegativity of carbon is certainly not the highest on the periodic table. That distinction belongs to fluorine, with an electronegativity value of 4.0, which makes it the most reactive of all elements. Fluorine is at the head of Group 7, the halogens, all of which are highly reactive and most of which have high electronegativity values. If one ignores the noble gases, which are virtually unreactive and occupy the extreme right-hand side of the periodic table, electronegativity values are highest in the upper right-hand side of the table--the location of fluorine--and lowest in the lower left. In other words, the value increases with group or column number (again, leaving out the noble gases in Group 8), and decreases with period or row number.
With an electronegativity of 2.5, carbon ties with sulfur and iodine (a halogen) for sixth place, behind only fluorine; oxygen (3.5); nitrogen and chlorine (3.0); and bromine (2.8). Thus its electronegativity is high, without being too high. Fluorine is not likely to form the long chains for which is carbon is known, simply because its electronegativity is so high, it overpowers other elements with which it comes into contact. In
Organic chemistry is the study of carbon, its compounds, and their properties. The only major carbon compounds considered inorganic are carbonates (for instance, calcium carbonate, alluded to above, which is one of the major forms of mineral on Earth) and oxides, such as carbon dioxide and carbon monoxide.
The term "organic" in everyday language connotes "living," but organic chemistry is involved with plenty of compounds not part of living organisms: petroleum, for instance, is an organic compound. It should be stressed that organic compounds do not have to be produced by living things, or even by things that once were alive; they can be produced artificially in a laboratory.
The breakthrough event in organic chemistry came in 1828, when German chemist Friedrich Wцhler (1800-1882) heated a sample of ammonium cyanate (NH4OCN) and converted it to urea (H2N-CO-NH2). Ammonium cyanite is an inorganic material, whereas urea, a waste product in the urine of mammals, is an organic one.
Ammonium cyanate and urea are isomers: substances having the same formula, but possessing different chemical properties. Thus they have exactly the same numbers and proportions of atoms, yet these atoms are arranged in different ways. In urea, the carbon forms an organic chain, and in ammonium cyanate, it does not.
Carbon, together with other elements, forms so many millions of organic compounds that even introductory textbooks on organic chemistry consist of many hundreds of pages. Fortunately, it is possible to classify broad groupings of organic compounds. The largest and most significant is that class of organic compounds known as hydrocarbons--chemical compounds whose molecules are made up of nothing but carbon and hydrogen atoms.
Every molecule in a hydrocarbon is built upon a "skeleton" composed of carbon atoms, either in closed rings or in long chains. The chains may be straight or branched.
Theoretically, there is no limit to the number of possible hydrocarbons. There are two basic varieties of hydrocarbon, distinguished by shape: aliphatic and aromatic. The first of these forms straight or branched chains, as well as rings, while the second forms only benzene rings, discussed below. Within the aliphatic hydrocarbons are three varieties: those that form single bonds (alkanes), double bonds (alkenes), and triple bonds (alkynes.)
The alkanes are also known as saturated hydrocarbons. The formula for any alkane is CnH2n+2, where n is the number of carbon atoms. In the case of a linear, unbranched alkane, every carbon atom has two hydrogen atoms attached, but the two end carbon atoms each have an extra hydrogen.
· Methane (CH4).
· Ethane (C2H6).
· Propane (C3H8).
· Butane (C4H10).
· Pentane (C5H12).
· Hexane (C6H14).
· Heptane (C7H16).
· Octane (C8H18).
The first four, being the lowest in molecular mass, are gases at room temperature, while the heavier ones are oily liquids. It should be noted that from butane on up, the alkanes have numerous structural isomers, depending on whether they are straight or branched, and these isomers have differing chemical properties.
Cycloalkanes are alkanes joined in a closed loop to form a ring-shaped molecule. They are named by using the names above, with cyclo-as a prefix. These start with propane, or rather cyclopropane, which has the minimum number of carbon atoms to form a closed shape: three atoms, forming a triangle.
Alkenes and alkynes.
The names of the alkenes, hydrocarbons that contain one or more double bonds per molecule, are parallel to those of the alkanes, but the family ending is-ene. Likewise they have a common formula: CnH2n. Both alkenes and alkynes, discussed below, are unsaturated--in other words, some of the carbon atoms in them are free to form other bonds. Alkenes with more than one double bond are referred to as being polyunsaturated.
As with the alkenes, the names of alkynes (hydrocarbons containing one or more triple bonds per molecule) are parallel to those of the alkanes, only with the replacement of the suffix -yne in place of-ane. The formula for alkenes is CnH2n-2. Among the members of this group are acetylene, or C2H2, used for welding steel. Plastic polystyrene is another important product from this division of the hydrocarbon family. carbon electronegativity polystyrene chemical
Aromatic hydrocarbons, despite their name, do not necessarily have distinctive smells. In fact the name is a traditional one, and today these compounds are defined by the fact that they have benzene rings in the middle. Benzene has a formula C6H6, and a benzene ring is usually represented as a hexagon (the six carbon atoms and their attached hydrogen.
With carbon and hydrogen as the backbone, the hydrocarbons are capable of forming a vast array of hydrocarbon derivatives by combining with other elements. These other elements are arranged in functional groups--an atom or group of atoms whose presence identifies a specific family of compounds.
Alcohols are oxygen-hydrogen molecules wedded to hydrocarbons. The two most important commercial types of alcohol are methanol, or wood alcohol; and ethanol, which is found in alcoholic beverages, such as beer, wine, and liquor. Used in adhesives, fibers, and plastics, it can also be applied as a fuel. Ethanol, too, can be burned in an internal-combustion engine, when combined with gasoline to make gasohol. Another significant alcohol is cholesterol, found in most living organisms. Though biochemically important, cholesterol can pose a risk to human health.
Aldehydes and ketones both involve a double-bonded carbon-oxygen molecule, known as a carbonyl group. In a ketone, the carbonyl group bonds to two hydrocarbons, while in an aldehyde, the carbonyl group is always at the end of a hydrocarbon chain. One prominent example of a ketone is acetone, used in nail polish remover. Aldehydes often appear in nature--for instance, as vanillin. The ketones carvone and camphor impart the characteristic flavors of spearmint leaves and caraway seeds.
Carboxylic acids and esters.
Carboxylic acids all have in common what is known as a carboxyl group, designated by the symbol -COOH. This consists of a carbon atom with a double bond to an oxygen atom, and a single bond to another oxygen atom that is, in turn, wedded to a hydrogen. All carboxylic acids can be generally symbolized by RCOOH, with R as the standard designation of any hydrocarbon.
When a carboxylic acid reacts with an alcohol, it forms an ester. An ester has a structure similar to that described for a carboxylic acidl. One well-known ester is acetylsalicylic acid--better known as aspirin. Esters, which are a key factor in the aroma of various types of fruit, are often noted for their pleasant smell.
Polymers are long, stringy molecules made of smaller molecules called monomers. They appear in nature, but thanks to Carothers--a tragic figure, who committed suicide a year before Nylon made its public debut--as well as other scientists and inventors, synthetic polymers are a fundamental part of daily life.
The structure of even the simplest polymer, polyethylene.
Polyethylene, for instance, is the plastic used in garbage bags, electrical insulation, bottles, and a host of other applications. A variation on polyethylene is Teflon, used not only in nonstick cookware, but also in a number of other devices, such as bearings for low-temperature` use. Polymers of various kinds are found in siding for houses, tire tread, toys, carpets and fabrics, and a variety of other products far too lengthy to enumerate.
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