A Little Bit of Organic Chemistry
The Beginning of Organic Chemistry
In 1828, Friedrich Wohler synthesized urea, found only in urine, from ammonium cyanate, an inorganic compound:
Ammonium cyanate, NH4CNO + heat yields urea, NH2CONH2
Wohler's synthesis of a compound previously available only through an organic process is considered as the start of the science of organic chemistry.
Plant Growth and Photosynthesis
During the same timeframe, the early part of the nineteenth century, Renee de Saussure proved that plants mainly grow from atmospheric carbon dioxide and water from the soil. This process, which depends on the ability of chlorophyll to absorb energy from sunlight, came to be called photosynthesis and is expressed by the general formula:
(6x)CO2 + (5x)H2O -> (C6H10O5)x + (6x)O2
where (C6H10O5)x is cellulose, one of the main components of plants, and (6x)O2 is the oxygen that the process releases to the atmosphere.
Frequently Encountered Terms
The following table defines some terms used in organic chemistry that are frequently encountered when decribing the chemical composition of plants.
Note: For the definitions of some additional chemical terms, see A Little Bit of General Chemistry.
| Compound | Definition | Example(s) | |
|---|---|---|---|
| A compound derived from a hydrocarbon by substituting a hydroxyl group (OH) for one or more of the hydrogen atoms. An alcohol possessing one hydroxyl group is known as a monohydric alcohol, two hydroxyl groups a dihydric alcohol, and three hydroxyl groups a trihydric alcohol. |
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| A compound derived from a hydrocarbon by substituting an oxygen atom in place of two hydrogen atoms on a carbon atom at the end of the chain of carbon atoms. The overall structure is shown here. | Formaldehyde, derived from methane. | ||
| Hydrocarbons where the carbon atoms are connected together in a chain. | Methane Series, also known as alkanes or parafins, general formula CnH2n+2. Alkanes are saturated hydrocarbons, that is, the carbon atoms in the chain are all connected by single bonds. The lower members of this series, that is those with the fewest carbon atoms, are gases under ordinary conditions: methane, ethane, propane, butane. The next members of this series are liquids: pentane, hexane, heptane, octane. As more caron atoms are added the compounds become oiler, then waxlike, and finally solid. Note: "Octane" in this case refers to a straight-chain hydrocarbon with eight carbon atoms. It does not refer to the "iso-octane" used as a standard for gasoline knock characteristics. Ethylene Series, also known as alkenes or olefins, general formula CnH2n. Alkenes are unsaturated hydrocarbons, that is, the carbon atoms in the chain are not all connected by single bonds. Alkene chains contain carbon atoms that are connected by double bonds. Acetylene Series, also known as alkynes, general formula CnH2n-2. Alkynes are unsaturated hydrocarbons, that is, the carbon atoms in the chain are not all connected by single bonds. Alkyne chains contain carbon atoms that are connected by triple bonds. |
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| The general definition of the term alkaloid is a nitrogeneous base
derived from a plant and having marked physiological effects. All alkaloids have at least one nitrogen atom in a carbon ring; replcing a carbon atom with a nitrogen atom makes the ring heterocyclic.
Chemically, alkaloids exhibit a very wide range of structures so that no more
precise definition is possible.
Note: Protoalkaloids, which are generally included in discussions of alkaloids, have a nitrogen atom outside the carbon ring. |
Many important compounds are categorized as alkaloids. Examples include atropine, caffeine, morphine, nicotine, and reserpine. The simplest alkaloid is conline, which is contained in the seeds and other parts of the Poison Hemlock, Conium maculatum. This was the poison used to kill the Greek philosopher Socrates, around 400 B.C. Conline was the first natural alkaloid to be synthesized, which was carried out by Ladenburg in 1886. | ||
| Alkyl is the general name of the hydrocarbon group in an alkane in which one hydrogen atom has been replaced by some other atom. If the atom that substitues for the hydrogen atom is a halogen (that is, flourine, iodine, bromine, or chlorine), the resulting compound is known as an alkyl halide. An alkyl halide is a mono-halogen alkane derivative; where more than one hydrogen atom has been substituted the compound is a poly-halogen alkane derivative. The name of the alkyl group is derived from the name of the parent hydrocarbon, for example methane or ethane.< The alkyl group by itself is referred to as an alkyl radical. | The simplest alkyl halide methyl chloride, CH3Cl. An historically important poly-halogen derivative is the anesthetic methyl trichloride, CHCl3, better known as chloroform. | ||
| A carboxyl and an amine group combined in the same function. | A peptide link, which joins amino acid molecules into peptide chains. | ||
| A compound derived from ammonia, NH3, by substituting organic groups in place of one or more of the hydrogen atoms. | Methylamine, CH3NH2, derived from methyl alcohol and ammonia. Amino acids. | ||
| Negative ions. In an electric field, anions move toward the positive electrode, the anode. | In common table salt, NaCl, Cl- is the anion. | ||
| Hydrocarbons where 6 carbon atoms are connected together in a ring. Rings may be joined together to create fused or condensed rings. Benzene, which has one ring, is considered to be the basic aromatic molecule. | Benzene Series; Napthalene Series (two fused rings); Anthracene Series (three fused rings). | ||
| Carbohydrates are compounds of carbon, hydrogen, and oxygen. They have the empirical formula C6H12O6.
Note: While hydrogen and oxygen are present in the ratio of 2:1 as in water, carbohydrates are not actually hydrates of carbon. Their chemical behavior is different than what their name suggests. Because simple sugars are easily oxidized in the tissues, they provide a ready source of energy. |
Sugars, of which the simplest is glucose, C6H12O6, also known as grape sugar. Simple sugars are known as monosaccarides. Many naturally occuring substances are polysaccharides, or complex sugars. | ||
Carboxylic (Organic) Acid |
An acid containing a carboxyl group, -COOH. | The simplest carboxylic acid is formic acid, obtained by distilling ants, HCOOH. Th most familiar carboxylic acid is acetic acid, in the dilute form of vinegar. Acetic acid can be produced by the oxidation of ethyl alcohol:
C2H5OH + O2 --> CH3COOH + H2O This reaction takes place in wine that is left exposed to the air. Microorganisms, called mother of vinegar, that are present in the wine ferment the ethyl alcohol to vinegar. |
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| Positive ions. In an electric field, cations move toward the negative electrode, the cathode. | In common table salt, NaCl, Na+ is the cation. | ||
| A complex sugar that can be split into two simple sugars through hydrolysis. They have the empirical formula C12H22O11. | Sucrose (cane sugar, beet sugar), maltose (malt sugar) and lactose (milk sugar) are disaccarides.
Note: Sucrose and maltose are isomers; they have the same molecular formula, but a different structure. Sucrose can be split into glucose (dextrose) fructose (fruit sugar). This process takes place very slowly in pure water, but is catalized to a high rate by the presence of hydrochloric acid. The enzyme sucrase (also known as invertase or saccharase), found in the mucosa of the intestine, is an organic catalyst for the hydroysis of sucrose. The overall formula is: C12H22O11 + H2O ---> C6H12O6 + C6H12O6 Note: Glucose and fructose are isomers; they have the same molecular formula, but a different structure. In the formula, one molecule of glucose and one molecule of fructose are produced for each molecule of sucrose that is hydrolyzed. |
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| An ester results from the combinaton of an organic acid and an alcohol. When these two compounds combine, the hydrogen atom on the carboxyl group of the organic acid is replaced by the alkyl radical, CnH2n+1, from the alcohol. The hydroxyl group from the alcohol combines with the hydrogen atom from the organic acid to form water. | Oils, fats, and waxes, which are esters of fatty acids and glycerol.
Note: Biodiesel is made from vegetable oil. For more information on this subject, see Collaborative Biodiesel Tutorial. |
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| Compounds consisting of an alkyl radical connected to a carboxyl group</>. | The higher members of this series occur as esters of glycerol (glycerides), in other words fats, so all members of this series are called fatty acids. The two most common saturated fatty acids are palmitic and stearic. The palmitic glyceride is the main constituent of palm oil. The stearic glyceride is the main constituent of animal fat.
Notes:
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| Compounds of a simple sugar and a compound containing a hydroxyl (-OH) group. The hydroxyl-containing compounds include alkaloids, terpenes, and phenols. The sugar component of the molecule is called the glycone; the nonsugar component is called the aglycone. | Glycosides are often named after the sugar they contain, for example, glucosides are based on glucose.Many important glycosides are obtained from plants.
These include salicin, from the bark of the willow tree,
from which aspirin was derived. Salicin is a phenol-based glycoside.
Vanilla flavoring (vanillin) is obtained from the immature fruit pods of the orchid, Vanilla planifolia. The pods contain the glycoside glucovanillin (Vanillin beta-glucoside), which is hydrolized by an enzyme in a fermentation process to glucose and vanillin . A number of plants contain poisonous, cyanogenic, glycosides that can be hydrolized to produce prussic acid (hydrocyanic acid, hydrogen cyanide, HCN). Many members of the Rose Family, Rosaceae, the Prunus subfamily in particular, contain the cyanogenic glycoside amygdalin in their pits. These include apricot, peach, plum, almond and bitter almond, and sweet and sour cherries. Glycosides that act on the heart are known as a cardiac glycosides. The powerful heart stimulant digitalis, obtained from the leaves of the purple foxglove, is a steroid cardic glycoside. |
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Hydrocarbon |
Compounds containing hydrogen and carbon | Aliphatic Hydrocarbons; Aromatic Hydrocarbons | |
| A reaction between a substance and water. Often used to split a complex substance into simpler substances. | Splitting sucrose into glucose and fructose. | ||
| A compound derived from a hydrocarbon by substituting an oxygen atom in place of two hydrogen atoms on a carbon atom that is not at the end of the chain of carbon atoms. | Acetone, derived from propane. | ||
| A simple sugar. There are two types: aldehyde-type and ketone-type | Glucose (dextrose) is the simplest aldehyde-type sugar.
Note: Glucose and fructose are isomers; they have the same molecular formula, but a different structure. Fructose (fruit sugar) is the simplest ketone-type sugar. Note: Glucose can be converted to fructose by means of an enzyme. Corn syrup that has had part of its glucose converted to fructose, so that the overall concentration of fructose is 14%, is known as high-fructose corn syrup (HFCS). HFCS is twice as sweet as sucrose and is the main sweetner used in soft drinks. Commercial beekeepers feed HFCS to honey bees as a source of carbohydrate. |
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Organic (Carboxylic) Acid |
A compound derived from a hydrocarbon by substituting an oxygen atom and a hydroxyl (OH) group in place of three hydrogen atoms on any carbon atom. This substitution forms the carboxyl group, COOH, which is present in all organic acids and gives them their acidic properties. More than one carboxyl group may be present. Because the hydroxyl (basic group) function predominates over the carboxyl function, organic acids are described in terms of the number of basic groups present. An organic acid with one carboxyl group is referred to as monobasic. If the acid has two carboxyl groups it is dibasic and so on. | Acetic acid, derived from ethane. Fatty acids, which are found in fats. | |
| Phenol (carbolic acid) and the compounds derived from it. Phenol itself is the monohydroxy derivative of benzene. | Phenol is a very reactive substance with powerful antispectic properties. Other antisepctics and disinfectants are typically measured against it. Other phenols, such as thymol, which is found in mint and oil of thyme and carvacrol, found in oil of caraway, also have antiseptic properties. | ||
| Carbohydrates that can be split by hydrolysis into more than two monosaccharides. They have the empirical formula (C6H10O5)n. | Starch (in plant cells) and cellulose (in the walls of plant cells) are the two most familiar examples of polysaccarides. They provide plants with a means of storage for carbohydrates. Glycogen, also known as animal starch, is found in the muscles and the liver and is the means by which animals store carbohydrates. | ||
| Glucosides contained in the roots of some plants. In water, they form a lather and several have been used as natural detergents. If taken internally, they cause vomiting and diarrhea. The empirical formula for saponins is C32H54O18. | Licorice Glycyrrhiza glabra, Glycyrrhiza echinata Yucca Yucca baccata, Yucca Glauca |
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| An oil, consisting of the esters of three fatty acids with each glycerol (glycerine) molecule. Glycerol has three -OH groups, so it can form tri-esters triglycerides. The three esterified fatty acids on each molecule may be the same but are typically different. A particular oil may include a number of fatty acids. | Linseed oil, also known as flaxseed oil. |
