Organic chemistry is the chemistry of the compounds of carbon.
The misleading name ‘organic’ is a relic of the days when chemical compounds were divided into two classes, inorganic and organic, depending upon where they ad come from. Inorganic compounds were those obtained from minerals; organic compounds were those obtained from vegetable or animal sources, that is, from material produced by living organisms. Indeed until about 1850 many chemists believed that organic compounds must have origin in living organisms, and consequently could never be synthesized from inorganic materials.
These compounds from organic sources had this in common: they all contained the element carbon. Even after it has become clear that these compounds did not have to come from living sources but could be made in the laboratory, it was convenient to keep the name organic to describe them and compounds like them. The division between inorganic and organic compounds has been retained to this day.
Today, although many compounds of carbon are still most conveniently isolated from plants and animals sources, most of them are synthesized. They are sometimes synthesized from inorganic substances like carbonates like cyanides, but more often from organic compounds. There are two large reservoirs of organic materials from which simple organic compounds are obtained: petroleum and coal. (Both of these are ‘organic’ in the old sense, being product of the decay of plants and animal). These simple compounds are used as building blocks from which larger and more complicated compounds can be made.
Petroleum and coal are recognize as fossil fuels, laid down over millennia and non-renewable. They—particularly—petroleum are being consumed at an alarming rate to meet our constantly increasing demands for power. Today, less than ten percent of petroleum used goes to making of chemicals; most of it is burnt simply to supply energy. There are, fortunately, alternative sources of power – solar, geothermal,, wind tides, nuclear energy,-- but where are we to find an alternate reservoir of organic raw material? Eventually, of course, we shall have to go to a place where the fossil fuels originally came from – the biomass – but this time directly, without the intervening millennia. The biomass is renewable and, used properly, can last as long on this planet as we can. In the meantime, it has been suggested, petroleum is too valuable to burn.
What is so special about the compounds of carbon that they should be separated from compounds of all the other hundred-odd elements of the periodic table? In fact, at least, the answer seams to be this: there are so very many compounds of carbon, and their molecules could be so large and complex.
The number of compounds that contain carbon is so many times grater than the number of compounds that do not contain carbon. These organic compounds have been divided into families, which generally have no counterparts among inorganic compounds.
Organic molecules containing thousands of atoms are known, and the arrangement of atoms in even small molecules can be very complicated. One of the major problems in organic chemistry is to find how the atoms are arranged in molecules, that is, to determine the structure of compounds.
There are many ways in which these complicated molecules can brake apart, or rearrange themselves, to form new molecules; there are many ways in which atoms can be added to these molecules, or new atoms are substituted for old ones. Much of organic chemistry is devoted to finding out what theses reaction are, how they take place, and how they can be used to synthesis compounds we want.
What is so special about carbon that it should form so many compounds? The answer to this question came to August Kekule in 1854 during a London bus ride.
Carbon atoms can attach themselves to one another to an extent not possible for atoms of any other element. Carbon atoms can form chains thousands of atoms long, or ring of all sizes; the chain and the rings can have branches and cross links. To the carbon atoms of these chains and rings there are attached to other atoms, chiefly hydrogen, but also fluorine, chlorine, bromine, iodine, oxygen, nitrogen, sulphur, phosphorus and many others.
Each different arrangement of atoms corresponds to a different compounds, and each compound has its own characteristic set of chemical and physical properties. It is not surprising that more than ten million compounds of carbon are known today and that this number is growing by half a million a year. It is not surprising that the study of their chemistry is a special field.
Organic chemistry is a field of immense importance to technology: it is the chemistry of dyes and drugs, paper and ink, paints and plastics, gasoline and rubber tire; it is the chemistry of the food we eat and the clothes we wear.
Organic chemistry is fundamental to biology and medicine. Aside from water, living organisms are made up of chiefly of organic compounds; the molecules of ‘molecular biology’ are organic molecules. Biology, on the molecular level, is organic chemistry.
It is not farfetched to say that we are living in the Age of Carbon. Every day the newspapers bring to our attention compounds of carbon: cholesterol and polyunsaturated fats, growth hormones and steroid, insecticides and pheromones, carcinogens and chemotherapeutic agents, DNA and genes. Wars are fought over petroleum. Twin catastrophes threaten us, both arising from the accumulation in the atmosphere of compounds of carbon: depletion of the ozone layer, due chiefly to the chlorofluorocarbons; and the greenhouse effect, due to methane, chlorofluorocarbons, and most of all,, carbon dioxide. It is perhaps symbolic that for 1990 the journal Science selected as the molecule of the year diamond, one of the allotropic forms of carbon. And a runner-up was another, newly discovered allotrope of carbon, C60 buckminsterfullerene – which has generated excitement in the chemical world not seen, it has been said, “since the days of Kekule”.
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