1. Introduction.
In the aerobic environment, the most dangerous by product are the species of reactive oxygen. The role of antioxidants is to detoxify reactive oxygen intermediates (ROI) in the body. Over the past several years, nutritional antioxidants have attracted considerable interest in the popular press as potential treatment for a wide variety of disease states, including cancer and other causes e.g. cancer, chronic inflammatory diseases and aging (Delany L. 1993).
The phrase "carbon-based life forms," is often used in science-fiction books and movies by aliens to describe the creatures of Earth, the only planet known to support life. Not only all living things contain carbon but also carbon is in plenty of things that were once living and now are the source for living, which makes it useful for dating the remains of past settlements on Earth. Of even greater usefulness is petroleum, a substance containing carbon-based forms that died long ago, became fossilized, and ultimately changed chemically into fuels. Then again, not all materials containing carbon were once living creatures; yet because carbon is a common denominator to all living things on Earth, the branch of study known as organic chemistry is devoted to the study of compounds containing carbon. Though among the most important organic compounds are the many carboxylic acids that are vital to life, carbon is also present in numerous important inorganic compounds, most notably its small but unavoidable compounds such as carbon dioxide, carbon monoxide and carbonates.
Carbon's name comes from the Latin word carbo, or charcoal which, indeed, is almost pure carbon. Its chemical symbol is C is generally crowned with its atomic number of 6, meaning that there are six protons in its nucleus. Its two stable isotopes are 12C, which constitutes 98.9% of all carbon found in nature, and 13C, which accounts for the other 1.1%. The mass of the 12C atom is the basis for the atomic mass unit (amu), by which mass figures for all other elements are measured: the amu is defined as exactly 1/12 the mass of a single 12C atom. The difference in mass between 12C and 13C, which is heavier because of its extra neutron, account for the fact that the atomic mass of carbon is 12.01 amu: were it not for the small quantities of 13C present in a sample of carbon, the mass would be exactly 12.00 amu.
Carbon makes up only a small portion of the known elemental mass in Earth's crust, oceans, and atmosphere (just 0.08%, or 1/1250 of the whole) yet it is the fourteenth most abundant element on the planet. In the human body, carbon is second only to oxygen in abundance, and accounts for 18% of the body's mass. Thus if a person weighs 100 lb (45.3 kg), he/she is carrying around 18 lb (8.2 kg) of carbon, interestingly the same material from which the cherished and much valued diamonds are made. Present in the inorganic rocks of the ground and in the living creatures above it, carbon is everywhere. Combined with other elements, it forms carbonates, most notably calcium carbonate (CaCO3), which appears in the form of limestone, marble, and chalk. In combination with hydrogen, it creates hydrocarbons, present in deposits of fossil fuels: natural gas, petroleum, and coal. In the environment, carbon, in the form of carbon dioxide (CO2), is taken in by plants, which undergo the process of photosynthesis and release oxygen for sustenance of animals that breathe in oxygen and release carbon dioxide to the atmosphere.
We know that carbon forms tetravalent bonds, and makes multiple bonds with a single atom. In addition, we have mentioned the fact that carbon forms long chains of atoms and varieties of shapes. But how does it do these things, and why? These are so good questions that an entire branch of chemistry, organic chemistry, is devoted to answering these theoretical questions, as well as to determining solutions to a host of other, more related and practical problems. Organic chemistry is the study of carbon, its compounds, and their properties. At one time, chemists thought that “organics” were synonymous with "living," and even as recently as the early nineteenth century, they believed that organic substances contained a supernatural "life force." Then, in 1828, German chemist Friedrich Wöhler cracked the code that distinguished the living from the nonliving species, and the organic from the inorganic.
Wöhler took a sample of ammonium cyanate (NH4OCN), and by heating it, converted it into urea (H2N-CO-NH2), a waste product in the urine of mammals. In other words, he had turned an inorganic material into an organic one, and he did so, as he observed, "without benefit of a kidney, a bladder, or a dog." It was almost as though he had created life. In fact, what Wöhler had glimpsed—and what other scientists who followed came to understand, was this: ‘what separates the organic from the inorganic is the manner in which the carbon chains are arranged’.
Ammonium cyanate and urea have exactly the same numbers and proportions of atoms, yet they are different compounds. They are thus isomers: substances which have the same formula, but are different chemically. In urea, the carbon forms an organic chain, and in ammonium cyanate, it does not. Thus, to reduce the specifics of organic chemistry even further, it can be said that this area of the field constitutes the study of carbon chains, and ways to rearrange them in order to create new substances.
Rubber, vitamins, cloth, and paper are all organically based compounds we encounter in our daily lives. In each case, the material comes from something that once was living, but what truly make these substances organic in nature is the common denominator of carbon, as well as the specific arrangements of the atoms. We have organic chemistry to thank for any number of things: aspirins and all manner of other drugs; preservatives that keep food from spoiling; perfumes and toiletries; dyes and flavorings, and so on.
It may not be out of context to mention that radiocarbon dating is used to date the age of charcoal, wood, and other biological materials as when an organism is alive, it incorporates a certain ratio of carbon-12 in proportion to the amount of the radioisotope (that is, radioactive isotope) carbon-14 that it receives from the atmosphere. As soon as the organism dies, however, it stops incorporating new carbon, and the ratio between carbon-12 and carbon-14 will begin to change as the carbon-14 decays to form nitrogen-14. Carbon-14 has a half-life of 5,730 years, meaning that it takes that long for half the isotopes in a sample to decay to nitrogen-14. Therefore a scientist can use the ratios of carbon-12, carbon-14, and nitrogen-14 to guess the age of an organic sample. The problem with radiocarbon dating, however, is that there is a good likelihood the sample can become contaminated by additional carbon from the soil. Furthermore, it cannot be said with certainty that the ratio of carbon-12 to carbon-14 in the atmosphere has been constant throughout time.
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Chemistry is a science of substances, their properties, and how and why materials combine or separate to form different substances. Atoms, molecules and compounds are the involved ones in the study of Chemistry. In other words, it is how atoms interact to form molecules and how molecules interact with each other. It also looks into the composition of substances and their properties. The outer electron orbits or shells primarily determine the chemical characteristics of a material and whether materials will chemically combine. Thus Chemistry is the study of the composition of matter and the changes that take place in that composition. If we place a bar of iron outside our window, the iron bar will soon begin to rust. If we pour vinegar on baking soda, the mixture fizzes. If we hold a sugar cube over a flame, the sugar begins to turn brown and give off steam. The goal of chemistry is to understand the composition of substances such as iron, vinegar, baking soda, and sugar and to understand what happens during the changes described here.
The term chemistry has grown out of an earlier field of study known as alchemy. Alchemy has been described as a kind of pre-chemistry, in which scholars studied the nature of matter but without the formal scientific approach that modern chemists use. The term alchemy is probably based on the Arabic name for Egypt, al-Kimia, or the "black country." Ancient scholars learned a great deal about matter, usually by trial- and-error methods. For example, the Egyptians mastered many technical procedures such as making different types of metals, manufacturing colored glass, dying cloth, and extracting oils from plants. Alchemists of the Middle Ages discovered a number of elements and compounds and perfected other chemical techniques, such as distillation and crystallization. The modern subject of chemistry did not appear, however, until the eighteenth century. At that point, scholars began to recognize that research on the nature of matter had to be conducted according to certain specific rules. Among these rules was one stating that ideas in chemistry had to be subjected to experimental tests. Nowadays keeping in view the overall significance and versatility of chemistry, we can say that:
Chemistry is a science: There is only one sanctioned procedure for determining whether a statement about matter is really chemistry: the exhaustive, inefficient, but highly successful scientific method. Chemists often arrive at new results by nonscientific means (like luck or sheer creativity), but their work isn't chemistry unless it can be reproduced and verified scientifically.
Chemistry is a systematic study: Chemists have devised several good methods for solving problems and making observations. For example, analytical chemists often use protocols (thoroughly tested recipes) for determining the concentrations of substances in a sample. Chemists use well-defined techniques like spectroscopy and chromatography to study new or unknown substances.
Chemistry is the study of the composition and properties of matter: Chemistry is the study of the composition and properties of matter as it answers questions like, "What kind of stuff is a sample made of? What does the sample look like on a molecular scale? How does the structure of the material determine its properties? How do the properties of the material change when we increase temperature, or pressure, or some other environmental variable?"
Chemistry is the study of the reactivity of substances: Chemistry is the study of the reactivity of substances as one material can be changed into another by a chemical reaction. A complex substance can by made from simpler ones. Chemical compounds can break down into simpler substances. For example, fuels burn, food cooks, leaves turn their colors in the fall, cells grow, medicines cure and it is both their chemistry and the chemistry which is concerned with the essential processes that make these changes happen. Today, the science of chemistry is often divided into four major areas: organic, inorganic, physical, and analytical chemistry. Each discipline investigates a different aspect of the properties and reactions of matter.
Organic chemistry: Organic chemistry is the study of carbon compounds. That definition sometimes puzzles beginning chemistry students because more than 100 chemical elements are known. How does it happen that one large field of chemistry is devoted to the study of only one of those elements and its compounds? The answer to that question is that carbon is a most unusual element. It is the only element whose atoms are able to combine with each other in apparently endless combinations. Many organic compounds consist of dozens, hundreds, or even thousands of carbon atoms joined to each other in a continuous chain. Other organic compounds consist of carbon chains with other carbon chains branching off them. Still other organic compounds consist of carbon atoms arranged in rings, cages, spheres, or other geometric forms. The scope of organic chemistry can be appreciated by knowing that more than 90 percent of all compounds known to science (more than 10 million compounds) are organic compounds. Organic chemistry is of special interest because it deals with many of the compounds that we encounter in our everyday lives: natural and synthetic rubber, vitamins, carbohydrates, proteins, fats and oils, cloth, plastics, paper, and most of the compounds that make up all living organisms, from simple one-cell bacteria to the most complex plants and animals.
Inorganic chemistry: Inorganic chemistry is the study of the chemistry of all the elements in the periodic table except for carbon. Like their cousins in the field of organic chemistry, inorganic chemists have provided the world with countless numbers of useful products, including fertilizers, alloys, ceramics, household cleaning products, building materials, water softening and purification systems, paints and stains, computer chips and other electronic components, and beauty products. The more than 100 elements included in the field of inorganic chemistry have a staggering variety of properties. Some are gases, others are solid, and a few are liquid. Some are so reactive that they have to be stored in special containers, while others are so inert (inactive) that they virtually never react with other elements. Some are so common they can be produced for only a few cents a pound, while others are so rare that they cost hundreds of dollars an ounce. Because of this wide variety of elements and properties, most inorganic chemists concentrate on a single element or family of elements or on certain types of reactions.
Physical chemistry: Physical chemistry is the branch of chemistry that investigates the physical properties of materials and relates these properties to the structure of the substance. Physical chemists study both organic and inorganic compounds and measure such variables as the temperature needed to liquefy a solid, the energy of the light absorbed by a substance, and the heat required to accomplish a chemical transformation. A computer is used to calculate the properties of a material and compare these assumptions to laboratory measurements. Physical chemistry is responsible for the theories and understanding of the physical phenomena utilized in organic and inorganic chemistry.
Analytical chemistry: Analytical chemistry is that field of chemistry concerned with the identification of materials and with the determination of the percentage composition of compounds and mixtures. These two lines of research are known, respectively, as qualitative analysis and quantitative analysis. Two of the oldest techniques used in analytical chemistry are gravimetric and volumetric analysis. Gravimetric analysis refers to the process by which a substance is precipitated (changed to a solid) out of solution and then dried and weighed. Volumetric analysis involves the reaction between two liquids in order to determine the composition of one or both of the liquids.
In the last half of the twentieth century, a number of mechanical systems have been developed for use in analytical research. For example, spectroscopy is the process by which an unknown sample is excited (or energized) by heating or by some other process. The radiation given off by the hot sample can then be analyzed to determine what elements are present. Various forms of spectroscopy are available (X-ray, infrared, and ultraviolet, for example) depending on the form of radiation analyzed. Other analytical techniques now in use include optical and electron microscopy, nuclear magnetic resonance (MRI; used to produce a three-dimensional image), mass spectrometry (used to identify and find out the mass of particles contained in a mixture), and various forms of chromatography (used to identify the components of mixtures).
Other fields of chemistry: The division of chemistry into four major fields is in some ways misleading and inaccurate. In the first place, each of these four fields is so large that no chemist is an authority in any one field. An inorganic chemist might specialize in the chemistry of sulfur, the chemistry of nitrogen, the chemistry of the inert gases, or in even more specialized topics. Secondly, many fields have developed within one of the four major areas, and many other fields cross two or more of the major areas. For an example of specialization, the subject of biochemistry is considered a subspecialty of organic chemistry. It is concerned with organic compounds that occur within living systems. An example of a cross-discipline subject is bioinorganic chemistry. Bioinorganic chemistry is the science dealing with the role of inorganic elements and their compounds (such as iron, copper, and sulfur) in living organisms. At present, chemists explore the boundaries of chemistry and its connections with other sciences, such as biology, environmental science, geology, mathematics, and physics. A chemist today may even have a so-called nontraditional occupation. He or she may be a pharmaceutical salesperson, a technical writer, a science librarian, an investment broker, or a patent lawyer, since discoveries by a traditional chemist may expand and diversify into a variety of fields that encompass our whole society.
Chemists have two major goals. One is to find out the composition of matter in order to learn what elements are present in a given sample and in what percentage and arrangement. This type of research is known as analysis. A second goal is to invent new substances that replicate or are different from those found in nature. This form of research is known as synthesis. In many cases, analysis leads to synthesis. That is, chemists may find that some naturally occurring substance is a good painkiller. That discovery may suggest new avenues of research that will lead to a synthetic (human-made) product similar to the natural product, but with other desirable properties (and usually lower cost). Many of the substances that chemistry has produced for human use have been developed by this process of analysis and synthesis.
--------------------------------------------------------------------------------------------Dr.Badruddin Khan teaches Chemistry in the University of kashmir, srinagar, India. His E.mail is:khanbudr@yahoo.co.in
Article Source: http://www.articlesbase.com/science-articles/chemistry-and-goals-of-chemists-570403.html
While organic chemistry is considered as the branch of chemistry in which the compounds of carbon are studied, the name organic goes back to a much earlier time in history when chemists thought that chemical compounds in living organisms were fundamentally different from those that occur in nonliving things. Their belief was that the chemicals that could be extracted from or that were produced by living organisms had a special "vitalism" or "breath of life" given to them by some supernatural being. As such, they presented fundamentally different kinds of problems than did the chemicals found in rocks, minerals, water, air, and other nonliving entities. The chemical compounds associated with living organisms were given the name organic to emphasize their connection with life. In 1828, German chemist Friedrich Wöhler, who found a very simple way to convert chemical compounds from living organisms into comparable compounds from nonliving entities, proved that this theory of vitalism was untrue. Consequently, the definition of organic chemistry changed as a result of Wöhler's research. The new definition was based on the observation that every compound discovered in living organisms had one property in common; they all contained the element carbon. As a result, the modern definition of organic chemistry, as the study of compounds of carbon, was adopted.
One important point that Wöhler's research showed was that the principles and techniques of chemistry apply equally well to compounds found in living organisms and nonliving things. Nonetheless, some important differences between organic and inorganic (not organic) compounds exist. These include the following:
1. The number of organic compounds vastly exceeds the number of inorganic compounds. The ratio of carbon-based compounds to non-carbon-based compounds is at least ten to one, with close to 10 million organic compounds known today. The reason for this dramatic difference is a special property of the carbon atom: its ability to join with other carbon atoms in very long chains, in rings, and in other kinds of geometric arrangements. It is not at all unusual for dozens, hundreds, or thousands of carbon atoms to bond to each other within a single compound—a property that no other element exhibits.
2. In general, organic compounds tend to have much lower melting and boiling points than do inorganic compounds.
3. In general, organic compounds are less likely to dissolve in water than are inorganic compounds.
4. Organic compounds are likely to be more flammable but poorer conductors of heat and electricity than are inorganic compounds.
5. Organic reactions tend to take place more slowly and to produce a much more complex set of products than do inorganic reactions.
The huge number of organic compounds requires that some system be developed for organizing them. The criterion on which those compounds are organized is the presence of various functional groups. A functional group is an arrangement of atoms that is responsible for certain characteristic physical and chemical properties in a compound. For example, one such functional group is the hydroxyl group, consisting of an oxygen atom and hydrogen atom joined to each other. It is represented by the formula —OH. All organic compounds with the same functional group are said to belong to the same organic family. Any organic compound that contains a hydroxyl group, for instance, is called an alcohol. All alcohols are similar to each other in that: (1) they contain one or more hydroxyl groups, and (2) because of those groups, they have similar physical and chemical properties. For example, alcohols tend to be more soluble in water than other organic compounds because the hydroxyl groups in the alcohol form bonds with water molecules.
The simplest organic compounds are the hydrocarbons, compounds that contain only two elements: carbon and hydrogen. The class of hydrocarbons can be divided into subgroups depending on the way in which carbon and hydrogen atoms are joined to each other. In some hydrocarbons, for example, carbon and hydrogen atoms are joined to each other only by single bonds. A single bond is a chemical bond that consists of a pair of electrons. Such hydrocarbons are known as saturated hydrocarbons. In other hydrocarbons, carbon and hydrogen atoms are joined to each other by double or triple bonds. A double bond consists of two pairs of electrons, and a triple bond consists of three pairs of electrons. The symbols used for single, double, and triple bonds, respectively, are —, =, and ?. Hydrocarbons containing double and triple bonds are said to be unsaturated. Hydrocarbons can also be open-chain or ring compounds. In an open-chain hydrocarbon, the carbon atoms are all arranged in a straight line, like a strand of spaghetti. In a ring hydrocarbon, the carbons are arranged in a continuous loop, such as a square, a pentagon, or a triangle.
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Dr.Badruddin Khan teaches Chemistry in the University of Kashmir, Srinagar, India
Article Source: http://www.articlesbase.com/college-and-university-articles/importance-of-functional-groups-in-organic-chemistry-623415.html
Organic chemistry is the chemistry of carbon compounds. All organic compounds contain carbon; however, there are some compounds of carbon that are not classified as organic. For example, salts such as carbonates (e.g., Na2CO3, CaCO3) and cyanides (e.g., NaCN, KCN) are usually designated as inorganic. Perhaps a more useful description might be: Organic compounds are compounds of carbon that usually contain hydrogen and that may also contain other elements such as oxygen, nitrogen, sulfur, phosphorus, or halogen (F, Cl, Br, or I). In any case, there are very few carbon compounds that are not organic, while there are millions that are.
Prehistoric civilizations obtained many useful chemicals from plants and animals. They were familiar with sugar, which they learned to ferment to make wine. Then they found that the wine could turn into vinegar. Ancient Egyptians used blue dye made from the indigo in madder root, and a royal purple dye extracted from a rare kind of mollusk. Soap was made by heating animal fat with base from wood ashes.
During the Middle Ages dry distillation of wood yielded mixtures of methyl alcohol, acetone, and acetic acid. Alchemists isolated cholesterol from gallstones, morphine from opium, and drugs such as quinine, strychnine, and brucine from various plants. Two hundred years ago chemists such as Antoine Lavoisier determined the elemental composition of many of these substances and noted that they all contained carbon and hydrogen, and that many also contained oxygen and nitrogen. It also appeared that there were two classes of materials: the mineral type (generally hard, high-melting, and noncombustible), and the organic type (often soft, liquid or low melting solids, and frequently easily combustible materials). Most organic chemicals could be burned to produce carbon dioxide; and any hydrogen present was converted to water (H2O). Because organic compounds had for centuries been isolated only from plants and animals, it was commonly believed that some "vital force" in living things was necessary to produce them. This belief persisted until 1828, when Friedrich Wöhler was able to make urea, a chemical found in the urine of animals, from the inorganic salt ammonium cyanate.
Since that time organic chemistry has grown into a vast and ever expanding field that encompasses millions of chemical compounds.
The field of organic chemistry includes more than twenty million compounds for which properties have been determined and recorded in the literature. Many hundreds of new compounds are added every day. Much more than half of the world's chemists are organic chemists. Some new organic compounds are simply isolated from plants or animals; some are made by modifying naturally occurring chemicals; but most new organic compounds are actually synthesized in the laboratory from other (usually smaller) organic molecules. Over the years organic chemists have developed a broad array of reactions that allow them to make all kinds of complex products from simpler starting materials.
When one considers the millions of chemical compounds that are known and notes that more than 95 percent of them are compounds of carbon, one realizes that carbon is unique. Why are there so many carbon compounds? It turns out that atoms of carbon are quite remarkable in a number of ways.
Carbon atoms form very strong bonds with other carbon atoms. The bonds are so strong that carbon can form long chains, some containing thousands of carbon atoms. (Carbon is the only element that can do this.)
A carbon atom forms four bonds, therefore carbon not only can form long chains, but it also forms chains that have branches. It is a major reason why carbon compounds exhibit so much isomerism. The simple compound decane (C10H22), for example, has 75 different isomers .
Carbon atoms can be bonded by double or triple bonds as well as single bonds. This multiple bonding is much more prevalent with carbon than with any other element.
Carbon atoms can form rings of various sizes. The rings may be saturated or unsaturated. The unsaturated 6-membered ring known as the benzene ring is the basis for an entire subfield of "aromatic" organic chemistry.
Carbon atoms form strong bonds not only with other carbon atoms but also with atoms of other elements. In addition to hydrogen, many carbon compounds also contain oxygen. Nitrogen, sulfur, phosphorus, and the halogens also frequently occur in carbon compounds.
Various kinds of functional groups occur widely among carbon compounds, and many different kinds of isomers are possible.
Compounds of carbon and hydrogen only are called hydrocarbons. These are the simplest compounds of organic chemistry. The most basic group of hydrocarbons are the alkanes, which contain only single bonds. The simplest member of the alkane series is methane, CH4, the main component of natural gas. The names of some alkanes are listed in Table 1. Alkanes sometimes
| ALKANES | |||
| Formula | Name | ||
| CH4 | CH4 | methane | gases |
| C2H6 | CH3CH3 | ethane | |
| C3H8 | CH3CH2CH3 | propane | |
| C4H10 | CH3CH2CH2CH3 | butane | |
| C5H12 | CH3(CH2)3CH3 | pentane | liquids |
| C6H14 | CH3(CH2)4CH3 | hexane | |
| C7H16 | CH3(CH2)5CH3 | heptane | |
| C8H18 | CH3(CH2)6CH3 | octane | |
| C9H20 | CH3(CH2)7CH3 | nonane | |
| C10H22 | CH3(CH2)8CH3 | decane | |
| C11H24 | CH3(CH2)9CH3 | undecane | |
| C12H26 | CH3(CH2)10CH3 | dodecane | |
| C13H28 | CH3(CH2)11CH3 | tridecane | |
| C14H30 | CH3(CH2)12CH3 | tetradecane | |
| C15H32 | CH3(CH2)13CH3 | pentadecane | |
| C16H34 | CH3(CH2)14CH3 | hexadecane | |
| C17H36 | CH3(CH2)15CH3 | heptadecane | |
| C18H38 | CH3(CH2)16CH3 | octadecane | solids |
| C19H40 | CH3(CH2)17CH3 | nonadecane | |
| C20H42 | CH3(CH2)18CH3 | eicosane | |
have ring structures. Since a 4-carbon chain of the alkane series is called butane, a ring of 4 carbon atoms is called cyclobutane.
Simple hydrocarbons that contain one or more double bonds are called alkenes. They are named like alkanes, but their names end in " –ene." The simplest alkene has two carbon atoms and is called ethene. A 3-carbon chain that has a double bond is called propene.
A 5-carbon hydrocarbon chain with a double bond is called pentene, and if the double bond links the second and third carbons, it is 2-pentene. Like cycloalkanes, alkenes have the general formula CnH2n. Alkenes having ring structures are called cycloalkenes. A 5-carbon ring with a double bond is called cyclopentene.
Hydrocarbons that contain one or more triple bonds are called alkynes, and is the name ending is "–yne." A 2-carbon alkyne is therefore named ethyne. (However, the compound is often referred to by its common name, which is acetylene. )
Compounds that contain double or triple bonds are said to be "unsaturated"—because they are not "saturated" with hydrogen atoms. Unsaturated compounds are reactive materials that readily add hydrogen when heated over a catalyst such as nickel. The reverse reaction also occurs. Heating ethane with steam is an important commercial process for making ethene (or ethylene). This is an important commercial process called "steam cracking."
When a 6-carbon ring contains 2 double bonds, it is called cyclohexadiene, but when it has 3 double bonds, it is not called cyclohexatriene; this is because a 6-carbon ring with three double bonds takes on a special kind of stability. The double bonds become completely conjugated and no longer behave as double bonds. The ring, known as a "benzene ring," is said to be aromatic.
The removal of a hydrogen atom from a hydrocarbon molecule leaves an alkyl group that readily attaches to a functional group, or forms a branch on a hydrocarbon chain. The groups are named after the corresponding hydrocarbons. For example, CH3– is named methyl; CH3CH2–, ethyl; CH2= CH–, ethenyl; CH3CH2CH2–, propyl; and so on. A benzene ring from which a hydrogen atom has been removed is often referred to as a phenyl. The branched molecules shown here would be given names as follows
Theoretically there is no limit to the length of hydrocarbon chains. Very large hydrocarbon molecules (polymers) have been made containing as many as 100,000 carbon atoms. However, such molecules are hard to make and very difficult to melt and to shape into useful products.
Hydrocarbons are obtained primarily from fossil fuels—especially petroleum and natural gas. Natural gas is a mixture that is largely methane mixed with varying amounts of ethane and other light hydrocarbons, while petroleum is a complex mixture of many different hydrocarbons. Coal, the other fossil fuel, is a much more complicated material from which many kinds of organic compounds, some of them hydrocarbons, can be obtained.
Alkane molecules are rather unreactive (except for being very flammable), but alkenes react with many other substances. When a drop of bromine is added to an alkene, for example, the deep orange color of the bromine immediately disappears as the bromine adds across the double bond to form a dibromo derivative. The double bond is called a "functional group" because its presence in a molecule causes reactivity at that particular site. There are a dozen or so functional groups that appear frequently in organic compounds. Some of the most common ones are listed in Table 2. The same molecule may contain several functional groups. Aspirin, for example, is both a carboxylic acid and an ester , and cholesterol is an alkene as well as an alcohol.
Isomers are molecules with the same molecular formula but different structures. There is only one structure for methane, ethane, or propane; but butane, C4H10, can have either of two different structure:
The linear molecule (1) is called butane, or normal butane (n -butane), whereas the branched molecule (2) is methylpropane (rather than 2-methylpropane, as the methyl group has to be in a 2-position). If the methyl group of (2) were attached to a terminal carbon, the resultant molecule would be the same as (1). Methylpropane (2) is also called iso butane.
In a conjugated system, there are alternating double and single bonds, allowing electrons to flow back and forth. Molecules that contain such conjugated systems are said to be stabilized by "resonance." In the benzene ring every other bond is a double bond, all the way around the ring. This results in a special kind of stabilization called "aromaticity," in which the electrons are delocalized and free to travel all around the ring. Certain ring compounds, like benzene, that contain such a conjugated system of double and single bonds are described as "aromatic."
Pentane has 3 isomers: pentane (or n -pentane), methylbutane (or iso- pentane), and dimethyl propane (or neo pentane). Hexane has 5 isomers: hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane. Heptane has 9 different isomers, octane has 18, nonane has 35, and decane has 75. An increase in the number of carbon atoms greatly increases the possibilities for isomerism. There are more than 4,000 isomers of C15H32 and more than 366,000 isomers of C20H42. The formula C30H62 has more than 4 billion. Of course, most of them have never been isolated as pure compounds (but could be, if there were any point in doing it).
For molecules other than hydrocarbons, still other kinds of isomers are possible. The simple formula C2H6O can represent ethyl alcohol or dimethyl ether; and C3H6O could stand for an alcohol, an ether, an aldehyde , or a ketone (among other things). The larger a molecule is, and the greater the variety of atoms and functional groups it contains, the more numerous its isomers.
There is still another kind of isomerism that stems from the existence of "right-" and "left-handed" molecules. It is sometimes referred to as optical isomerism because the molecules that make up a pair of these isomers usually differ only in the way they rotate plane polarized light.
There are so many millions of organic compounds that simply finding names for them all is a major challenge. It was not until the late nineteenth century that chemists developed a logical system for naming organic compounds. Compounds had often been named according to their sources. The 1-carbon carboxylic acid, for example, was first obtained from ants, and so it was called formic acid, from the Latin word for ants (formicae ). The 2-carbon acid was obtained from vinegar (acetum in Latin), and was called acetic acid.
To bring some order to the naming process an international meeting was held in 1892 at Geneva, Switzerland. The group later became known as the International Union of Pure and Applied Chemistry (IUPAC). Its objective was to establish a naming process that would provide each compound with a unique and systematic name. An initial set of rules was adopted at that first meeting in Geneva, and IUPAC has continued that work. Its systematic naming rules are used by organic chemists all over the world. The names of the alkanes form the basis for the system, with functional groups usually being indicated with appropriate suffixes. Some examples are given in Table 2.
Organic chemistry is concerned with the many compounds of carbon, their names, their isomers, and their properties, but it is mostly concerned with their reactions. Organic chemists have developed a huge array of chemical reactions that can convert one organic compound to another. Some reactions involve addition of one molecule to another; some involve decomposition of molecules; some involve substitution of one atom or group by another; and some even involve the rearrangement of molecules, with some atoms moving into new positions. Some reactions require energy in the form of heat or radiation; and some require a special kind of catalyst or some sort
| NAMING ORGANIC COMPOUNDS | |||||
| Functional Group | Type Compound | Example | IUPAC Name | Common Name | |
| C=C | double bond | alkene | H2C=CH2 | ethene | ethylene |
| C≡C | triple bond | alkyne | HC≡CH | ethyne | acetylene |
| –OH | hydroxyl | alcohol | CH3OH | methanol | methyl alcohol |
| –O– | oxy | ether | H3COCH3 | methoxymethane | methyl ether |
| carbonyl | aldehyde | H2C=0 | methanal | formaldehyde | |
| carbonyl | ketone | CH3COCH3 | propanone | acetone | |
| carboxyl | carboxylic acid | HCOOH | methanoic acid | formic acid | |
| carboxyl | ester | HCOOCH2CH3 | ethyl methanoate | ethyl formate | |
| –NH2 | amino | amine | CH3NH2 | aminomethane | methylamine |
| –CN | cyano | nitrile | CH3CN | ethanenitrile | acetonitrile |
| –X | halogen | haloalkane | CH3Cl | chloromethane | methyl chloride |
of solvent. Of course, not all organic reactions are highly successful. One reaction might be a very simple one giving essentially 100 percent of the desired product; but another might be a complex multistep process yielding less than 5 percent overall of the wanted product.
Organic reactions can often give remarkable control as to what products should be formed. Adding water to propene for example, produces 2-propanol in the presence of acid, but it yields 1-propanol if treated first with B2H6 and then H2O2 in the presence of base.
Fossil fuels have been our primary natural source for many organic chemicals for more than a century, but our fossil fuel resources are finite, and they are being rapidly depleted (especially oil and gas). What will be our sources of organic materials in the future? Since fossil fuels are nonrenewable resources, it is believed that the twenty-first century will see a shift toward greater dependence on renewable raw materials. The largest U.S. chemical company has a goal of becoming 25 percent based on renewable resources by 2010. It is already producing 1,3-propanediol from cornstarch using a gene-tailored E. coli bacterium. This diol is used in Du Pont's fiber Sorona, which is said to combine the best features of both polyester and nylon fibers. Succinic acid and polyhydroxybutyrate are also obtainable from renewable crops, and the list of such renewable raw materials is destined to grow. For example, ethylene (or ethene), CH2=CH2, which is a highly important commercial chemical used in making many industrial chemicals and polymers, is presently made by steam cracking of ethane obtained from oil or natural gas; but ethylene can also be made by dehydration of ethyl alcohol made by fermentation of sugar. Efforts are even being made to use biowaste materials, such as corn husks, nutshells, and wood chips as industrial raw materials.
Organic chemists often need to examine products for identification, purity analysis, or structure determination. There are some marvelous tools available to help them do these things. Chromatography , spectroscopy , and crystallography are especially widely used in organic chemistry.
Column chromatography, gas chromatography, and liquid chromatography are all important methods for separating mixtures of organic compounds. Spectroscopic tools include ultraviolet (UV), infrared (IR), nuclear magnetic resonance (NMR), and mass spectroscopy (MS), each capable of providing a different kind of information about an organic compound. Although it is limited to substances that can be prepared as pure crystals, x-ray crystallography is probably the ultimate tool for determining molecular structure.
Some organic chemists are involved in basic research at government or academic institutions, but most have careers in industry. The industries vary from oil and chemical companies to industries producing food, pharmaceuticals, cosmetics, detergents, paints, plastics, pesticides, textiles, or other kinds of products. Many organic chemists work in laboratories, where they do various kinds of analysis or research, but many others do not. Some are teachers, or writers, or science librarians. Some study law and become patent attorneys; some study medicine and become medical researchers; and some study business and become administrators of companies, colleges, or other institutions. Organic chemistry is an enormous field full of many kinds of career possibilities.
see also Fossil Fuels; Lavoisier, Antoine; Organic Halogen Compounds; WÖhler, Friedrich.
Kenneth E. Kolb
Atkins, Robert C., and Carey, Francis A. (2002). Organic Chemistry: A Brief Course, 3rd edition. Boston: McGraw-Hill.
Bailey, Philip S., Jr., and Bailey, Christina A. (2000). Organic Chemistry: A Brief Survey of Concepts and Applications, 6th edition. Upper Saddle River, NJ: Prentice Hall.
Brown, William H., and Foote, Christopher S. (2002). Organic Chemistry, 3rd edition. San Diego: Saunders.
Fessenden, Ralph J.; Fessenden, Joan S.; and Logue, Marshall (1998). Organic Chemistry, 6th edition. Pacific Grove, CA: Brooks/Cole.
Solomons, T. W. Graham (1997). Fundamentals of Organic Chemistry, 5th edition. New York: Wiley.
www.encyclopedia.com
Curie , family of French scientists. Pierre Curie, 1859-1906, scientist, and his wife, Marie Sklodowska Curie, 1867-1934, chemist and physicist, b. Warsaw, are known for their work on radioactivity and on radium. The Curies' daughter Irène (see under Joliot-Curie , family) was also a scientist.Article Source: http://www.articlesbase.com/science-articles/contributions-of-ancient-arabian-and-egyptian-scientists-on-chemistry-327375.html
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