However, researchers are investigating alternate and renewable sources, such as converting used frying oil usually plant-based to biodiesel [7] , or reclaiming waste oils from industrial processes [8]. Fossil Fuels. Nuclear Fuels.
Acid Rain. Climate Change. Climate Feedback. Carbon atoms form linked chains to which hydrogen atoms are attached. The simplest alkane has two carbon atoms and six hydrogen atoms C 2 H 6 ; this is the molecule ethane. Hydrocarbons of various types are abundant in the rocks of the earth and are a prime source of fuel coal, petroleum, natural gas. They are also the major component of waxes and oils and are frequently converted into important molecules such as plastic and other organic chemicals such as paint cosmetics, detergents and insecticides.
For example, methane, CH 4 , is the principal component of natural gas. Butane, C 4 H 10 , used in camping stoves and lighters is an alkane. Gasoline is a liquid mixture of continuous- and branched-chain alkanes, each containing from five to nine carbon atoms, plus various additives to improve its performance as a fuel. Kerosene, diesel oil, and fuel oil are primarily mixtures of alkanes with higher molecular masses. The main source of these liquid alkane fuels is crude oil, a complex mixture that is separated by fractional distillation.
Fractional distillation takes advantage of differences in the boiling points of the components of the mixture see Figure 5. You may recall that boiling point is a function of intermolecular interactions, which was discussed in the chapter on solutions and colloids.
Figure 5. The vapors rise through bubble caps in a series of trays in the tower. As the vapors gradually cool, fractions of higher, then of lower, boiling points condense to liquids and are drawn off.
No carbon-carbon bonds are broken in these reactions, and the hybridization of the carbon atoms does not change. For example, the reaction between ethane and molecular chlorine depicted here is a substitution reaction:. The C—Cl portion of the chloroethane molecule is an example of a functional group , the part or moiety of a molecule that imparts a specific chemical reactivity.
The types of functional groups present in an organic molecule are major determinants of its chemical properties and are used as a means of classifying organic compounds as detailed in the remaining sections of this chapter. Want more practice naming alkanes? Watch this brief video tutorial to review the nomenclature process. Organic compounds that contain one or more double or triple bonds between carbon atoms are described as unsaturated.
You have likely heard of unsaturated fats. These are complex organic molecules with long chains of carbon atoms, which contain at least one double bond between carbon atoms. Unsaturated hydrocarbon molecules that contain one or more double bonds are called alkenes.
Double and triple bonds give rise to a different geometry around the carbon atom that participates in them, leading to important differences in molecular shape and properties. The differing geometries are responsible for the different properties of unsaturated versus saturated fats.
Ethene, C 2 H 4 , is the simplest alkene. Each carbon atom in ethene, commonly called ethylene, has a trigonal planar structure. The second member of the series is propene propylene Figure 6 ; the butene isomers follow in the series. Four carbon atoms in the chain of butene allows for the formation of isomers based on the position of the double bond, as well as a new form of isomerism.
Figure 6. Expanded structures, ball-and-stick structures, and space-filling models for the alkenes ethene, propene, and 1-butene are shown. Ethylene the common industrial name for ethene is a basic raw material in the production of polyethylene and other important compounds.
Over million tons of ethylene were produced worldwide in for use in the polymer, petrochemical, and plastic industries. Ethylene is produced industrially in a process called cracking, in which the long hydrocarbon chains in a petroleum mixture are broken into smaller molecules. Polymers can be natural starch is a polymer of sugar residues and proteins are polymers of amino acids or synthetic [like polyethylene, polyvinyl chloride PVC , and polystyrene].
The variety of structures of polymers translates into a broad range of properties and uses that make them integral parts of our everyday lives. Adding functional groups to the structure of a polymer can result in significantly different properties see Chemistry in Everyday Life: Kevlar, later in this chapter.
An example of a polymerization reaction is shown in Figure 7. The monomer ethylene C 2 H 4 is a gas at room temperature, but when polymerized, using a transition metal catalyst, it is transformed into a solid material made up of long chains of —CH 2 — units called polyethylene.
Polyethylene is a commodity plastic used primarily for packaging bags and films. Figure 7. The reaction for the polymerization of ethylene to polyethylene is shown. Polyethylene is a member of one subset of synthetic polymers classified as plastics. Plastics are synthetic organic solids that can be molded; they are typically organic polymers with high molecular masses.
Most of the monomers that go into common plastics ethylene, propylene, vinyl chloride, styrene, and ethylene terephthalate are derived from petrochemicals and are not very biodegradable, making them candidate materials for recycling.
Recycling plastics helps minimize the need for using more of the petrochemical supplies and also minimizes the environmental damage caused by throwing away these nonbiodegradable materials. Plastic recycling is the process of recovering waste, scrap, or used plastics, and reprocessing the material into useful products.
For example, polyethylene terephthalate soft drink bottles can be melted down and used for plastic furniture, in carpets, or for other applications. Other plastics, like polyethylene bags and polypropylene cups, plastic food containers , can be recycled or reprocessed to be used again. Many areas of the country have recycling programs that focus on one or more of the commodity plastics that have been assigned a recycling code see Figure 8.
These operations have been in effect since the s and have made the production of some plastics among the most efficient industrial operations today. Figure 8. Each type of recyclable plastic is imprinted with a code for easy identification.
The name of an alkene is derived from the name of the alkane with the same number of carbon atoms. The presence of the double bond is signified by replacing the suffix -ane with the suffix -ene. The location of the double bond is identified by naming the smaller of the numbers of the carbon atoms participating in the double bond:. Molecules of 1-butene and 2-butene are structural isomers; the arrangement of the atoms in these two molecules differs. As an example of arrangement differences, the first carbon atom in 1-butene is bonded to two hydrogen atoms; the first carbon atom in 2-butene is bonded to three hydrogen atoms.
The compound 2-butene and some other alkenes also form a second type of isomer called a geometric isomer. In a set of geometric isomers, the same types of atoms are attached to each other in the same order, but the geometries of the two molecules differ. Carbon atoms are free to rotate around a single bond but not around a double bond; a double bond is rigid. This makes it possible to have two isomers of 2-butene, one with both methyl groups on the same side of the double bond and one with the methyl groups on opposite sides.
The 2-butene isomer in which the two methyl groups are on the same side is called a cis -isomer; the one in which the two methyl groups are on opposite sides is called a trans -isomer Figure 9. The different geometries produce different physical properties, such as boiling point, that may make separation of the isomers possible:.
Figure 9. These molecular models show the structural and geometric isomers of butene. This reaction is called an addition reaction. Key Points Hydrocarbons are molecules that contain only carbon and hydrogen. The bonding of hydrocarbons allows them to form rings or chains.
Key Terms covalent bond : A type of chemical bond where two atoms are connected to each other by the sharing of two or more electrons. Hydrocarbons Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen, such as methane CH 4. Hydrocarbon Chains Hydrocarbon chains are formed by successive bonds between carbon atoms and may be branched or unbranched. When two carbon atoms form a double bond, the shape is planar, or flat.
Single bonds, like those found in ethane, are able to rotate. Double bonds, like those found in ethene cannot rotate, so the atoms on either side are locked in place.
0コメント