Organic chemistry is the chemistry of carbon compounds; inorganic chemistry is the chemistry of compounds of all elements other than carbon.
Carbon atoms form four covalent bonds with each other as well as with other atoms.
The general properties of carbon compounds are:
Most carbon compounds are nonelectrolytes.
The reaction rates of carbon compounds are usually slow.
Many carbon compounds oxidize slowly in air but rapidly if heated.
Most carbon compounds are unstable at high temperatures.
12-2. Alkanes
The simplest carbon compounds, hydrocarbons, contain only carbon and hydrogen.
Alkanes are hydrocarbons whose molecules have only single carbon-carbon bonds.
Examples of alkanes include methane (CH4), propane (C3H8), and butane (C4H10).
Petroleum and natural gas consist largely of alkanes.
12-3. Petroleum Products
There are three processes by which petroleum products are derived:
Fractional distillation, in which crude oil is heated and its vapors are collected and condensed at progressively higher temperatures.
Catalytic cracking, in which heavy hydrocarbons are cracked into smaller molecules by heating them under pressure in the presence of catalysts.
Polymerization, in which the molecules of lighter hydrocarbons are polymerized by joining the smaller molecules into larger ones under the influence of heat, pressure, and catalysts.
Alkane molecules are nonpolar, insoluble in water, and rather chemically unreactive. These properties, plus their toxicity to living organisms, makes the discharge of petroleum and petroleum products into the sea a serious environmental matter.
12-4. Structural Formulas
Structural formulas represent the covalent bonds between the atoms of a molecule by dashes and show how the atoms are linked together. Each dash stands for a pair of shared electrons.
The number of bonds an atom forms in an organic compound is the same as the number of electrons it has to gain or lose to achieve a closed outer shell.
12-5. Isomers
Isomers are compounds that have the same molecular formulas but different structural formulas and properties.
Flipping a structural formula end-over-end does not give the formula of an isomer.
12-6. Unsaturated Hydrocarbons
The linkage of two adjacent carbon atoms in a carbon compound by the sharing of two electron pairs (two covalent bonds) is called a double bond.
Three electron pairs (three covalent bonds) are shared by adjacent carbon atoms in a triple bond.
Unsaturated compounds have double or triple carbon-carbon bonds and are more reactive than saturated compounds, which have only single carbon-carbon bonds (alkanes and similar compounds).
12-7. Benzene
Benzene, C6H6, is a clear liquid that is insoluble in water, has a strong odor, and has its six C atoms arranged in a flat hexagonal ring.
In benzene, six electrons are shared by the six carbon atoms in the ring and belong to the molecule as a whole and not to any particular pair of atoms. These electrons are delocalized.
Aromatic compounds are organic compounds that contain one or more benzene rings in their molecules.
Many aromatic compounds, such as toluene, have strong odors.
Aliphatic compounds are organic compounds that do not contain benzene rings.
12-8. Hydrocarbon Groups
Hydrocarbon derivatives are compounds obtained by substituting other atoms or atom groups for one or more of the H atoms in hydrocarbon molecules.
The carbon-hydrogen atom groups that appear in the hydrocarbon derivatives are named from the parent hydrocarbons.
A functional group is a group of atoms whose presence in an organic molecule largely determines its chemical behavior.
Some classes of organic compounds and their functional groups are:
Alcohols. Alcohols contain the hydroxyl group (—OH). Examples include ethanol, ethylene glycol, and glycerol. Ethanol in beverages is produced by fermentation of sugar by yeast enzymes.
Ethers. An ether has an oxygen atom bonded between two carbon atoms (– O –); ethers are widely used solvents.
Aldehydes and ketones. Aldehydes and ketones both contain the carbonyl atom group <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0072509791/169256/ssgCh12ieq02.jpg','popWin', 'width=106,height=123,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (2.0K)</a>. In aldehydes, the carbonyl group is at end of the molecule with a hydrogen atom attached to the carbon atom. In ketones, the carbonyl group is inside a molecule between adjacent carbon atoms. An example of an aldehyde is formaldehyde; and example of a ketone is acetone.
Organic acids. Organic acids contain the carboxyl group (—COOH). Examples include formic acid, acetic acid, and citric acid.
Esters. Esters contain the ester group <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0072509791/169256/ssgCh12ieq03.jpg','popWin', 'width=141,height=150,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (3.0K)</a>. Many esters have fruity or flowerlike odors. Examples include ethyl acetate, nitroglycerin, and animal and vegetable fats.
12-10. Polymers
A Polymer is a long chain of simple molecules (monomers) linked together.
Polymers that contain the vinyl group are classed as vinyls.
Some examples of polymers include Styrofoam, Teflon, Orlon, and Plexiglas (or Lucite). Plexiglas is thermoplastic, meaning it softens and can be shaped when heated but becomes rigid again on cooling.
A copolymer is a polymer that consists of two different monomers. Dynel and Saran Wrap are examples.
Certain monomers that contain two double bonds in each molecule form flexible, elastic polymers called elastomers; rubber and neoprene are examples.
Polyamides and polyesters are polymers produced by chemical reactions rather than by the polymerization of monomers.
Polyamides contain amide groups linking the structural elements. The synthetic fiber nylon is an example.
Polyesters contain ester groups linking their structural elements. The synthetic fiber Dacron is an example.
12-11. Carbohydrates
Carbohydrates are compounds of carbon, hydrogen, and oxygen atoms whose ratio between hydrogen atoms and oxygen atoms is 2 to 1. Examples include sugars and starches.
Monosaccharides are simple sugars. Glucose, fructose, galactose, and mannose are examples.
Disaccharides are composed of two simple sugar monomers per molecule. Examples are sucrose, lactose, and maltose.
Polysaccharides are complex sugars that consist of chains of more than two simple sugars. Examples include cellulose, starch, chitin, and glycogen.
The oxidation of glucose provide plants and animals with energy. The overall reaction is:
C6H12O6 + 6O2® 6CO2 + 6H2O + energy
Carbohydrates are broken down, or hydrolyzed, into simple sugars during digestion.
12-12. Photosynthesis
Photosynthesis is the reverse process of the oxidation of glucose. The overall reaction is
6CO2 + 6H2O + energy ® C6H12O6 + 6O2
Chlorophyll is the catalyst for photosynthesis. The energy comes from sunlight.
Atmospheric oxygen comes from photosynthesis.
12-13. Lipids
Lipids are organic compounds composed of the elements carbon, oxygen, and hydrogen, but contain less O relative to C and H than do carbohydrates. Examples include fats, oils, waxes, and sterols.
A fat molecule consists of a glycerol molecule with three fatty acid molecules attached.
Saturated fats are solids at room temperatures; unsaturated fats are liquids.
Fats provide nearly twice as much energy per gram than do carbohydrates.
Hydrogenation is used to convert liquid fat into solid fat to make margarine and other products. During hydrogenation, H atoms are added to the double-bonded C atoms in a liquid fat, which produces a solid fat.
Cholesterol is a lipid found in the bloodstream. Deposits of cholesterol within arteries can cause the serious condition atherosclerosis.
12-14. Proteins
Proteins are compounds of carbon, hydrogen, oxygen, nitrogen, and often sulfur and phosphorus. They are the chief constituents of living cells.
Proteins are composed of 20 different amino acids linked by peptide bonds to form polypeptide chains that are usually coiled or folded in intricate patterns.
The shape of a protein molecule and its sequence of amino acids give it a unique character that is reflected in its biological activity.
The human body can synthesize only some of the 20 amino acids needed to manufacture the proteins essential to life. The amino acids the body cannot synthesize must be provided in the diet.
12-15. Soil Nitrogen
Nitrogen compounds in the soil are removed by plants to supply nitrogen for the formation of plant proteins.
The decay of dead plants, animals, and animal wastes returns nitrogen to the soil but does not completely replenish what has been removed by plants.
Soil nitrogen is returned to the soil by two means:
"Nitrogen-fixing" bacteria convert atmospheric nitrogen into nitrogen compounds.
Lightning causes atmospheric nitrogen to combine with oxygen to form nitrogen oxides. These are returned to the earth in rainwater.
Man has disturbed the natural nitrogen cycle, resulting in a number of environmental problems.
12-16. Nucleic Acids
Nucleic acids consist of long chains of units called nucleotides.
Each nucleotide has three parts:
A phosphate group (PO4)
A pentose sugar: ribose (C5H10O5) in ribonucleic acid (RNA) and deoxyribose (C5H10O4) in deoxyribonucleic acid (DNA)
A nitrogen base
The nitrogen bases in DNA are adenine, guanine, cytosine, and thymine.
The nitrogen bases in RNA are the same as in DNA, except uracil replaces thymine.
DNA has the form of a double helix linked by the nitrogen bases; the sequence of these bases is the genetic code.
Chromosomes consist of DNA molecules.
DNA molecules govern protein synthesis in cells and, by making copies of themselves, can pass on the genetic code to new cells, thus ensuring that new cells have the same characteristics, or heredity, as the original cell.
Changes in the sequence of the bases in a DNA molecule can result in a mutation.
RNA differs from DNA in the following ways:
The sugar in RNA is ribose, not deoxyribose as in DNA.
RNA molecules are much smaller then DNA molecules.
RNA molecules usually consist of only single strands of nucleotides.
The set of coded DNA instructions for each protein is called a gene, and the entire collection of genes is called the genome of an organism.
James D. Watson and Francis H. C. Crick discovered the structure of DNA in 1953.
12-17. Origin of Life
Life probably originated in or near the early oceans when the composition of the atmosphere likely consisted of water, methane, ammonia, carbon dioxide, and hydrogen cyanide.
A certain portion of these gases were dissolved in the early oceans to form a sort of "chemical soup."
Of the reactions that took place in this chemical soup, five classes of important biological molecules likely formed. These are the sugars, glycerol, the fatty acids, the amino acids, and the nitrogen bases.
Reactions between these molecules likely lead to more complex compounds and ultimately to the first molecules able to replicate themselves. These eventually gave rise to the first primitive cells.
