The oxygen atoms combine with oxygen molecules to make ozone:. This ozone that is produced from this reaction absorbs ultraviolet light with wavelengths of nm or less, splitting into oxygen molecules and oxygen atoms,. The ozone in the ozone layer thus protects the surface of the Earth and more importantly, the living organisms that make their home there from much of the damaging high-energy ultraviolet light from the Sun.
When a molecule of Freon drifts into the upper atmosphere, photons of high-energy light can strike it, causing it to release a chlorine atom:. The chlorine atom has an unpaired electron, and is a highly reactive free radical , which reacts with ozone in the stratosphere, converting it to molecular oxygen:.
The chlorine atom is regenerated in this process, and behaves as a catalyst; one chlorine atom can destroy up to , ozone molecules. The mechanism for ozone destruction was first published in by F. Sherwood Rowland and Mario J. Molina; they shared the Nobel Prize in Chemistry in with Paul Crutzen, who proposed a similar mechanism for the destruction of ozone by nitrogen oxides in In , an international agreement called the Montreal Protocol on Substances that Deplete the Ozone Layer was signed.
This treaty cut back on the production and use of CFCs; in , partially in response to the alarming increase in the size of the "ozone hole" over the South Pole, the agreement was extended to become a ban on the use of CFCs starting in It is believed that CFC levels in the stratosphere will continue to rise through the s, and will not return to safe levels until the middle of the s.
CFCs in refrigeration are being replaced by hydrochlorofluorocarbons HCFCs , which are slightly more reactive than CFCs, and fall apart before reaching the stratosphere, and by hydrofluorocarbons HFCs ; in propellants they are being replaced mostly by carbon dioxide and low-boiling point hydrocarbons. The HCFCs are not fully halogenated — i. Because of this, these molecules are less stable than the CFCs, and degrade to a larger extent before they reach the upper atmosphere.
The HFCs contain only hydrogen, fluorine, and carbon, and are not damaging to the ozone layer. Freona is now widely used in the air conditioning systems of automobiles in place of Freon Download 3D Bromochlorodifluoromethane Halon is an example of a halon , a haloalkane that has bromine atoms in addition to chlorine and fluorine atoms.
Halons are very stable, and are useful in fire extinguishers, since they do not damage electronic equipment. Their use has largely been phased out under the Montreal Protocols see Freon above , but they are still used in fire suppression systems aboard some aircraft, since no completely satisfactory and safe alternatives have been discovered.
Dichlorodiphenyltrichloroethane DDT 3D Download 3D Dichlorodiphenyltrichloroethane , or 1,1,1-trichloro-2,2-bis- p -chlorophenyl ethane , better knows as DDT , is an very powerful insecticide. It was unique among the known insecticides at the time of its discovery in , in that it was effective against insects, but not very toxic to mammals.
DDT was widely used to kill mosquitoes that spread malaria, and was also effective against the insects that spread sleeping sickness and typhus. Unfortunately, DDT persists in the environment for a long time, and its accumulation in wildlife lead to decreases in the populations of several bird species. It is used in some shampoos to kill lice and other ectoparasites. However, it is a suspected carcinogen, and is banned in California, and several countries.
Chlordane 3D Download 3D Chlordane was used as a pesticide on some crops, and was also used to kill termites. Because of concerns about its toxicity, it was banned by the EPA in Atkins, Molecules , 2nd ed. Cambridge: Cambridge University Press, , p. Paula Yurkanis Bruice, Organic Chemistry , 4th ed.
Upper Saddle River: Prentice Hall, , p. Marye Anne Fox and James K. Whitesell, Organic Chemistry , 3rd ed. Sudbury: Jones and Bartlett Publishers, p. Maitland Jones, Jr. New York: W. Richard J. Lewis, Sr. New York: Van Nostrand Reinhold, Marc Loudon, Organic Chemistry , 4th ed. New York: Oxford University Press, , p.
Englewood Cliffs: Prentice Hall, , p. Sharp, The Penguin Dictionary of Chemistry , 2nd ed. London: Penguin Books, Truman Schwartz, Diane M. Bunce, Robert G.
Silberman, Conrad L. Stanitski, Wilmer J. Stratton, and Arden P. Dubuque: Wm. Brown Communicatiions, Inc. Wade, Jr. Martha Windholz ed. Number of Carbons Stem 1 meth- 2 eth- 3 prop- 4 but- 5 pent- 6 hex- 7 hept- 8 oct- 9 non- 10 dec-. There are five structural isomers of C 6 H 14 : Using common or non-systematic names is not practical for molecules with a large number of carbon atoms, since it would be necessary to memorize unique names for each possible compound.
Table 1. This molecule is often found on traffic signs: well, maybe not Cyclononane C 9 H 18 3D Download 3D Cyclononane is a ring of nine carbon atoms. The oxygen atoms combine with oxygen molecules to make ozone: This ozone that is produced from this reaction absorbs ultraviolet light with wavelengths of nm or less, splitting into oxygen molecules and oxygen atoms, which then re-combine to form ozone, which can absorb another photon of ultraviolet light.
When a molecule of Freon drifts into the upper atmosphere, photons of high-energy light can strike it, causing it to release a chlorine atom: The chlorine atom has an unpaired electron, and is a highly reactive free radical , which reacts with ozone in the stratosphere, converting it to molecular oxygen: The chlorine atom is regenerated in this process, and behaves as a catalyst; one chlorine atom can destroy up to , ozone molecules.
Bromochlorodifluoromethane Halon 3D Download 3D Bromochlorodifluoromethane Halon is an example of a halon , a haloalkane that has bromine atoms in addition to chlorine and fluorine atoms.
Navigation Bar. Molecule Gallery. Methane , CH 4. Download 3D. Ethane is an odorless, nontoxic, flammable gas, which has a boiling point of Propane is used as an industrial fuel, and in home heating and cooking.
Butane , like propane, burns cleanly, and is used in LPG fuels liquefied petroleum gas for outdoor cooking. Butane is an unbranched or "normal" alkane. Pentane is a liquid at room temperature, having a boiling point of Hexane has a boiling point of Heptane has a boiling point of Octane has a boiling point of Isooctane is a structural isomer of octane both are C 8 H 18 , but is branched compare with butane and isobutane.
Nonane has a boiling point of Decane has a boiling point of Hexadecane is typical for the number of carbons in the hydrocarbons present in diesel fuel.
S ummary of the Straight-Chain Alkanes. Cyclopropane C 3 H 6. Because free rotation is not possible around the single bonds in a cycloalkane, when two methyl groups are added to cyclopropane, there are two possible arrangements: both methyl groups can be pointing to the same side of the ring cis , or to opposite sides of the ring trans :. These molecules are not structural isomers of each other, because the order in which the atoms are connected is the same, but the two methyl groups are pointing in different directions in space, making them stereoisomers of each other.
Cyclobutane C 4 H 8. Cyclopentane C 5 H Cyclohexane C 6 H With cyclohexane, ring chemistry gets even more interesting and complicated. There are still a number of C—H eclipsing interactions, however, and this is not the lowest-energy conformation which is possible.
This is drastically oversimplified, of course; the chair and boat conformation represent the extremes of a large number of possible intermediate conformations, and the energetics of the ring system change a great deal when substituents are added to the ring.
Cycloheptane C 7 H There is a slight amount of strain energy in cycloheptane and larger cycloalkanes, since it is difficult for them to adopt bond angles of Cyclooctane C 8 H Cyclooctane is a ring of eight carbon atoms.
This molecule is often found on traffic signs: well, maybe not. Cyclononane C 9 H Cyclodecane C 10 H Decalin C 10 H Decalin , or bicyclo[4.
Norbornane , bicyclo[2. Adamantane is a tricyclic molecule; the fused cyclohexane rings in this molecule are extremely rigid. Cubane was first synthesized by Philip Eaton and Thomas W. Prismane is so named because it looks like a molecular prism duh. Propellane was first synthesized by K. Dodecahedrane is a molecule of the molecular formula C 20 H 20 which is shaped like a dodecahedron a polyhedron having twelve faces. Chloromethane Methyl chloride. Dichloromethane Methylene chloride.
Trichloromethane Chloroform. Tetrachloromethane Carbon Tetrachloride. Tetrachloromethane better known as carbon tetrachloride is a liquid at room temperature, with a density of 1. Dichlorodifluoromethane Freon Dichlorodifluoromethane Freon is an example of the chlorofluorocarbons CFCs, or freons , which are organic compound containing fluorine and chlorine atoms. Chlorodifluoromethane Freon Bromochlorodifluoromethane Halon Bromochlorodifluoromethane Halon is an example of a halon , a haloalkane that has bromine atoms in addition to chlorine and fluorine atoms.
You can also get octane by the process known as cracking. Maybe, but cracking involves passing the vapour of big molecules over a hot catalyst, which splits them into smaller molecules.
An example of a product produced by cracking is an alkene such as ethene MOTM December ; these reactive molecules are very useful to the chemical industry.
Picture of a cracker in Baton Rouge straight out of the Johnny Cash songbook. Well, isomers are compounds with the same molecular formula but different structures.
For example, octane has lots of isomers, like these three, all variants on C 8 H 18 :. So, the term isomerisation means converting one isomer into another one.
In the chemical industry this usually means converting a straight-chain octane into an isomer with more branches; these are valuable on account of their higher 'octane ratings'. First, you have to understand the engines in petrol-fuelled cars. Petrol engines are driven by the combustion of a mixture of a gaseous mixture of air and hydrocarbon fuel. This mixture is injected into the cylinder as the piston is on its downstroke, then gets compressed as the piston moves up.
At a particular point, a sparking plug fires a spark that ignites the mixture, forming a very hot mixture of carbon dioxide and steam, creating the power that forces the piston down, driving the engine and powering the wheels. This gave more power, but it was also likely that the fuel-air mixture would pre-ignite, before it was sparked. This was the work of an American chemist called Russell Marker photo, right. He started with heptane, a seven-carbon molecule that was very similar to octane.
Heptane caused really bad knocking, so next he tried 2,2,4-trimethylpentane, traditionally known as isooctane; it also has the formula C 8 H 18 so is an isomer of octane. This has a branched chain containing eight carbon atoms, but does not cause any knocking. Mixtures were made with varying amounts of heptane and isooctane, so that their knocking characteristics could be studied.
The higher the octane rating, the more the gas-air mixture can be compressed before it is ignited, and the more power you get when it burns. Yes, it means with the right fuel mixture, engines runs more smoothly, efficiently, and quietly.
And until the s, it was improved still further by the addition of tetraethyllead as an additional anti-knock agent. Nowadays, however, cars use 'lead-free' fuels due to issues with lead being found in the environment and the fact that it damages the catalytic converters that are fitted to modern cars see MOTM Jan It costs quite a lot of money to separate the isooctane from the other less desirable alkanes, so a mixture is used to keep costs down.
But octane fuel is used for some aircraft engines, and if you go back to the last century, high-octane fuel helped shape history.
Back in , British seaplane aircraft won the Schneider trophy a speed race for airplanes for Britain three times, with the help of high-octane fuels developed by Air Commodore Rod Banks and his colleagues. The designer R. Mitchell later developed these seaplanes into the Supermarine Spitfire fighter aircraft. Well, he became one of the few university professors not to have a PhD.
Just over 10 years after his work on octane ratings, he found a way of degrading diosgenin, found in Mexican yams, into progesterone, which became known as the Marker degradation, an example of semisynthesis at work. This ultimately led to oral contraceptives.
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