Fruit processors artificially introduce ethylene to hasten the ripening process exposure to as little as 0.1 mg of ethylene for 24 h can ripen 1 kg of tomatoes. Ripening fruits and vegetables give off ethylene, which triggers further ripening. Thus, until you become more familiar the language of organic chemistry, it is often most useful to draw out line or partially-condensed structures, as shown below:Īlkenes occur widely in nature. Note that the molecular formula for ethene is C 2H 4, whereas that for ethyne is C 2H 2. The double or triple bond nature of a molecule is even more difficult to discern from the molecular formulas. In an alkene, the double bond is shared by the two carbon atoms and does not involve the hydrogen atoms, although the condensed formula does not make this point obvious, ie the condensed formula for ethene is CH 2CH 2. Mathematically, this can be indicated by the following general formulas: As a result of the double or triple bond nature, alkenes and alkynes have fewer hydrogen atoms than comparable alkanes with the same number of carbon atoms. Collectively, they are called unsaturated hydrocarbons, which are defined as hydrocarbons having one or more multiple (double or triple) bonds between carbon atoms. Even so, it remained an important anesthetic into the 1960s, when it was replaced by nonflammable anesthetics such as halothane (CHBrClCF 3).īy definition, alkenes are hydrocarbons with one or more carbon–carbon double bonds (R 2C=CR 2), while alkynes are hydrocarbons with one or more carbon-carbon triple bonds (R–C≡C–R). Ethylene was thought to be safer, but it too was implicated in numerous lethal fires and explosions during anesthesia. However, it was discovered that acetylene forms explosive mixtures with air, so its medical use was abandoned in 1925. The two simplest unsaturated compounds-ethylene (ethene) and acetylene (ethyne)-were once used as anesthetics and were introduced to the medical field in 1924. Aromatic compounds serve as the basis for many drugs, antiseptics, explosives, solvents, and plastics (e.g., polyesters and polystyrene). However, due to the cyclic structure, the properties of aromatic rings are generally quite different, and they do not behave as typical alkenes. Thus, they have formulas that can be drawn as cyclic alkenes, making them unsaturated. Biologically important molecules, such as deoxyribonucleic acid, DNA (C) also contain an aromatic ring structures. Ultradur can be found in showerheads, toothbrush bristles, plastic housing for fiber-optics cables, and in automobile exterior and interior components. The repeating monomer of Ultradur is shown in (B). Ultradur, PBT is a plastic polymer that contains an aromatic functional group. Aromatic hydrocarbons contain the 6-membered benzene ring structure (A) that is characterized by alternating double bonds. PVC pipe installation photo provided by: Steve Tan.Īromatic hydrocarbons are defined by having 6-membered ring structures with alternating double bonds (Fig 8.2).įigure 8.2: Aromatic Hydrocarbons. Plexiglas aquarium photo provided by: Leonard G. Hip replacement photo provided by: The Science Museum London / Science and Society Picture Library. The polyvinylchloride repeating unit is shown in the lower left. Upper right, common PCV piping used as material being used for sewage and drains. The methylacrylate repeating unit is shown in the lower middle. Upper middle, shatterproof acrylic plexiglas used to build a large indoor aquarium. Upper left, a stainless steel and ultra high molecular weight polyethylene hip replacement. The polyethylene repeating unit is shown in the lower left. In fact, they serve as building blocks for many familiar plastics-polyethylene, vinyl plastics, acrylics-and other important synthetic materials (e.g., alcohols, antifreeze, and detergents).įigure 8.1 Common polymers made using alkene building blocks. Unsaturated hydrocarbons-hydrocarbons with double or triple bonds-on the other hand, are quite reactive. In Chapter 7, we noted that alkanes- saturated hydrocarbons-have relatively few important chemical properties other than that they undergo combustion and react with halogens. Our modern society is based to a large degree on the chemicals we discuss in this chapter.
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