Extending the structure of adamantane further into three dimensions results in the structure of diamonds. Cole at the University of Chicago in Prismane 3D Download 3D Prismane is so named because it looks like a molecular prism duh. Wiberg at Yale University. Dodecahedrane 3D Download 3D Dodecahedrane is a molecule of the molecular formula C 20 H 20 which is shaped like a dodecahedron a polyhedron having twelve faces.
It was first synthesized in by the research group of Leo A. Paquette at Ohio State University. Alkyl halides , or haloalkanes , are alkanes in which one or more hydrogen atoms are replaced by halogen atoms fluorine, chlorine, bromine, or iodine. The carbon-halogen bond is more polar than the carbon-hydrogen bonds, but most alkyl halides are not very soluble in water.
Alkyl fluorides and chlorides having only one halogen atoms have densities that are higher than those of alkanes, but are slightly less dense than water, while alkyl bromides and iodides are generally more dense than water. Alkyl halides having more than one halogen atom are often more dense than water. Alkyl halides are named as alkanes, with the halogens named as halo- substituents. The halogens are named as fluoro- , bromo- , chloro- , and iodo- when attached to a carbon atom.
For example, the name "1-chloropropane" indicated a three-carbon chain with a chlorine atom on carbon number 1. A number of simple alkyl halides are usually known by their common names; for instance, trichloromethane is almost always referred to as "chloroform.
It is a very common solvent, but it is mildly toxic; it is more dense than water, having a density of 1. It is sometime used as a paint remover and degreaser. It is used to decaffeinate coffee beans; since it has such a low boiling point, the residual solvent can be removed from the beans at fairly low temperatures. Chloroform is a commonly used organic solvent, and like dichloromethane is more dense than water d 1. Chloroform vapor is a anesthetic: James Young Simpson was the first to use chloroform as an anesthetic during childbirth in presumably, not on himself!
However, since chloroform is carcinogenic, and toxic to the liver, it is not widely used for this purpose anymore. It's also useful for knocking out giant apes. Tetrachloromethane Carbon Tetrachloride 3D Download 3D Tetrachloromethane better known as carbon tetrachloride is a liquid at room temperature, with a density of 1. It used to be a common organic solvent, and was widely used for dry cleaning and spot removal. However, it has been shown to be toxic and carcinogenic, so other solvents are used instead.
Carbon tetrachloride is also a contributor to ozone depletion see Freon , and has been banned under the Montreal Protocols that set strict limits on the use of CFCs. It was heavily used in dry cleaning, but it has been replaced by other solvents such as tetrachloroethylene under the Montreal Protocols see Freon Dichlorodifluoromethane Freon 3D Download 3D Dichlorodifluoromethane Freon is an example of the chlorofluorocarbons CFCs, or freons , which are organic compound containing fluorine and chlorine atoms.
These compounds were developed in the s for use as refrigerants; prior to this, ammonia was used as a refrigerant, but the high toxicity of ammonia gas made this less than ideal. The CFCs are relatively nontoxic, very unreactive, and boil at low temperatures, and were thus ideal for use in refrigeration equipment. In addition, CFCs were widely used as aerosol propellants in spray cans, and as foaming agents in the manufacture of plastic foams such as Styrofoam.
Unfortunately, the low reactivity of the CFCs leads to a major environmental problem: they persist in the environment for a long time up to a century , and eventually make their way into the upper atmosphere, where they damage the ozone layer. Ozone , O 3 , is an allotropic form of molecular oxygen, O 2 , which is found in the stratosphere, at an altitude of 10 to 50 km above the surface of the Earth.
It is produced when photons h n of high-energy ultraviolet light wavelengths of nm or less from the Sun splits oxygen molecules into oxygen atoms O. 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. The general formula for the straight-chain alkanes is H - CH 2 n - H.
Methane Ethane. Branched alkanes are derived from the straight-chain alkanes system by removing one of the hydrogen atoms from a methylene group -CH 2 - and replacing it with an alkyl group.
The smallest branched alkane is 2-methylpropane or isobutane Pictures shown above. These 2 compounds form a pair of isomers isos , Greeks, equal. Isomers are compounds with the same molecular formula but different structural formulae. For example, pentane has three possible isomers in which one is a linear straight-chain alkane and two are branched alkanes. Moreover, straight-chain alkanes are saturated compounds as there are no double or triple bonds between carbon atoms.
There are no side chains or pendant groups attached to the continuous carbon chain of these molecules. Branched chain alkanes are hydrocarbon compounds containing side groups attached to a continuous carbon chain. These side chains are named as branches. Therefore, these compounds are not linear hydrocarbons. Since they are alkanes, there are no double or triple bonds between carbon atoms.
Hence, these molecules are saturated compounds. The branches present in these molecules include methyl, ethyl, propyl, etc. Figure The ball-and-stick models of these two compounds show them to be isomers; both have the molecular formula C 4 H Notice that C 4 H 10 is depicted with a bent chain in Figure The four-carbon chain may be bent in various ways because the groups can rotate freely about the C—C bonds. However, this rotation does not change the identity of the compound.
It is important to realize that bending a chain does not change the identity of the compound; all of the following represent the same compound:. The formula of isobutane shows a continuous chain of three carbon atoms only, with the fourth attached as a branch off the middle carbon atom of the continuous chain. Unlike C 4 H 10 , the compounds methane CH 4 , ethane C 2 H 6 , and propane C 3 H 8 do not exist in isomeric forms because there is only one way to arrange the atoms in each formula so that each carbon atom has four bonds.
Next beyond C 4 H 10 in the homologous series is pentane. Each compound has the same molecular formula: C 5 H Table The compound at the far left is pentane because it has all five carbon atoms in a continuous chain.
0コメント