Chemistry - an illustrated guide to science (794128), страница 27
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If there is one carbonatom in the molecule it is:“meth” (1 carbon atom in the chain)+ “ane” (for alkane): methane.If there are four carbon atoms in themolecule it is:“but” (4 carbon atoms in the chain)+ “ane” (for alkane): butane.● The third example is propane, analken e with three carbon atoms:“pro” (3 carbon atoms in the chain)+ “ene” (for alkene).● The fourth example is ethyne, analkyn e with a two carbon chain:“eth” (2 carbon atoms in the chain)+ “yne” (for alkyne).HHH H H HH C C C C H4but-C H-anebutaneHH H H HHC HHH C C3prop-C C-enepropene2eth-C C-yneethyneH HHC C HH© Diagram Visual Information Ltd.●H156CHEMISTRY OF CARBONKey wordsalkanehomologousserieshydrocarbonvan der WaalsforcesThe first six alkanesThe alkan es form an hom ologou sseries of compounds that have thegeneral formula CnH2n+2, where n is apositive integer.
Each alkane moleculediffers from the previous one in theseries by -CH2- .● They have similar chemical propertiesand show a gradation of physicalproperties, such as melting point andboiling point, as the molecular sizeincreases.● Alkane molecules are attracted to eachother by van der Waals forces. Asmolecular size increases, there is moreoverlap between the molecules, andthe intermolecular forces of attractionincrease.● Alkane molecules are frequentlyshown as having a flat two-dimensionalstructure because this is easy to draw,but in reality, the four bonds aroundeach carbon atom are directed towardthe corners of a tetrahedron.
Theangle between any two bonds is109.5°.● Alkanes are relatively unreactivesubstances when compared with othergroups of hydrocarbon s. Their mostimportant reaction is combustion, andthey are the main constituent of arange of fuels. Natural gas is largelycomposed of methane:Table of the first sixalkanesAlkaneMethaneFormulaCH4C2H6C3H8HH HH H HH C HH C C HH C C C HHH HH H HEthanePropane●StructuralformulaBoilingpoint (°C)–164–87–42Physicalstate at roomtemperatureGasGasGasAlkaneButanePentaneHexaneFormulaC4 H10MolecularmodelStructuralformulaCH4 + 2O2 ➞ CO2 + 2H2O●In a good supply of air, hydrocarbonsburn to give carbon dioxide and water.In a restricted supply of air, carbonmonoxide and/or carbon may beformed:Boilingpoint (°C)C5H12C6 H14H H H HH H H H HH H H H H HH C C C C HH C C C C C HH C C C C C C HH H H HH H H H HH H H H H H03669GasLiquidLiquid© Diagram Visual Information Ltd.C2H6 + 2O2 ➞ CO + C + 3H2OPhysicalstate at roomtemperatureMolecularmodel157Table of the first fivealkenesCHEMISTRY OF CARBONKey wordsaddition reactionalkenefunctional grouphomologousseriesMolecularmodelThe first five alkenesThe alken es form an hom ologou sseries of compounds with the generalformula CnH2n, where n is a positiveinteger.
Each alkene molecule differsfrom the previous one in the series by-CH2- .● Alkene molecules are attracted to eachother by van der Waals forces. Asmolecular size increases, there is moreoverlap between the molecules, andthe intermolecular forces of attractionincrease. The series thus shows agradation of physical properties, suchas melting point and boiling point.● Alkenes all contain the samefu n ction al grou p, a carbon–carbondouble bond, represented by C=C.● The bonds around each of the carbonatoms in a carbon–carbon doublebond are in the same plane anddirected toward the corners of anequilateral triangle.
The angle betweenany two bonds is 120°.● Alkenes undergo combustion in thesame way as alkanes. However, theyhave other chemistry resulting fromthe reactive carbon–carbon doublebond.● Alkenes undergo addition reactions inwhich a molecule is added across thecarbon–carbon double bond.
Forexample, ethene undergoes thefollowing addition reaction s:HH H H HHH H H H HH C C C C C CHH H HHH H H HH C C C C CHH H3064LiquidLiquidGasHH H HH C C C CHH–6–47HH HH C C CHHHC CH–104GasGasCH2=CH2 + H-OH ➞ CH3-CH2-OHethene + steam ➞ ethanolCH2=CH2 + H-Br ➞ CH3-CH2Brethene + hydrogen bromide ➞bromoethaneCH2=CH2 + Br-Br ➞ CH2Br-CH2Brethene + bromine ➞ 1,2-dibromoethane© Diagram Visual Information Ltd.6C6 H12Hexene5C5H10Pentene43C3H6C4 H8ButeneEtheneC2H42CH2=CH2 + H-H ➞ CH3-CH3ethene + hydrogen ➞ ethanePropenePhysicalstate at roomtemperature●Boilingpoint (°C)StructuralformulaNumber ofcarbon atomsper moleculeFormulaAlkenevan der Waalsforces158CHEMISTRY OF CARBONKey wordsalkeneethaneetheneethanolgeometricisomerismhalogensisomerEthene1 Dehydration of ethanol to produce etheneabcdefaconcentrated sulfuric acidethanolheatalkali — to remove impuritieswateretheneEthene●Ethen e is the first member of thealken e series.
It is a colorless,flammable gas.f1 Preparation●bIn the laboratory, ethene can be madeby the dehydration of ethan ol usingconcentrated sulfuric acid.e2 Structure●Ethene, like all alkenes, contains acarbon–carbon double bond aboutwhich rotation is impossible.c-H2OCH3CH2OH ➞ CH2=CH2etheneethanol3 IsomerismIsom ers are compounds having thesame molecular formula and relativemolecular mass but different threedimensional structures.● The existence of two compounds withthe same molecular formula but wheregroups are distributed differentlyaround a carbon–carbon double bondis described as geom etric isom erismor cis / trans isomerism.● The prefix “cis” is used when thesubstituent groups (an atom or groupof atoms substituted in place of ahydrogen atom or chain) of ahydrocarbon are or the same side of aplane through the carbon–carbondouble bond. The prefix “trans” isused when the substituent groups areon the opposite side.● In trans-1,2-dibromoethene thebromine atoms are on opposite sidesof a plane through the carbon–carbondouble bond.● In cis-1,2-dibromoethene the bromineatoms are on the same side.●© Diagram Visual Information Ltd.d2 StructureHH3 IsomerismHC CHBrHC CHEtheneBrHC CHTrans-1, 2-dibromoetheneBrBrCis-1, 2-dibromoethene4 ReactivityCH2 = CH2 + Cl 2CH2Cl—CH2ClReaction with chlorine to form 1, 2-dichloroethaneCH2 = CH2 + H2NiCH3CH3Reaction with hydrogen to form ethane4 Reactivity●The carbon–carbon double bond inethene is very reactive and willundergo various addition reactions.Ethene reacts with: halogen s (such aschlorine) to form 1,2-dihaloethane,hydrogen to form ethan e, andhydrogen halides to form haloethane.CH2 = CH2 + HXReaction with hydrogen halides to form haloethaneCH3CH2X159PolymersCHEMISTRY OF CARBONKey words1 Types of branchingadditionpolymerizationbakeliteetheneApolyethenepolymerpolymerizationBPolymers●Polymer with few branched chains,e.g., high-density polyetheneA polym er is a large organic moleculecomposed of repeating carbon chains.The physical properties of a polymerdepend on the nature of these carbonchains and how they are arranged.1 Types of branchingA certain amount of side branchingoccurs during polym erization ,depending on the reaction conditions.● Low pressure and low temperatureresults in a high-density polymer.● Very high pressure and moderatetemperatures produce a low-densitypolymer.● In high-density polymers, the carbonchains are unbranched, and they canbe packed closely together forming adense substance, e.g., high-densitypolyethen e (1A).● In low-density polymers, the carbonchains are branched, and it is notpossible to pack them as closelytogether, e.g., low-density polyethene(1B).● In polymers like bakelite, there arecross links between the carbon chains,producing a hard, rigid structure (1C).●CPolymer with many branched chains,e.g., low-density polyethenePolymer with much cross-linking,e.g., bakelite2 Additional polymerization (illustrating how ethene can berestructured to form poly(ethylene) i.e., polyethene)HHC CHHHC CHHHC CHHHH HH HH HC CC CC CH HH HH HH H H H H HC C C C C CH H H H H H2 Addition polymerizationEthen e forms a polymer by a processcalled addition polym erization .● In this process, one of the bonds fromthe carbon–carbon double bond isused to form a bond with an adjacentmolecule.
This process is repeatedmany times, resulting in long chainscontaining thousands of carbon atoms.●© Diagram Visual Information Ltd.H160CHEMISTRY OF CARBONKey wordsalkenemonomerpolymerPolymers: formation1 Restructuring of propene to make poly(propene)CH3CMonomersClCHTetrafluoroethene molecules combineto form polytetrafluoroethene.● Trichloromethane is produced by thereaction of methane with controlledamounts of chlorine/hydrochloric acid.This is reacted with anhydroushydrogen fluoride in the presence ofantimony(III) chloride to givechlorodifluoromethane, which issubsequently cracked to producetetrafluoroethene.© Diagram Visual Information Ltd.CCCCHHHHHHClHCHClCCHHHCHClHClHClHCCCCCCHHHHHHH3 Poly(phenylethene)C6 H5C6 H5HC●●HCH3 HCC●4 FormingpolytetrafluoroetheneCHHCH3 HHCCH2 FormingpolychloroethenePhenylethene molecules combine toform polyphenylethene.● Phenylethane is made from etheneand benzene by a Friedel-Craftsreaction using aluminum(III)chloride/hydrochloric acid catalyst.This is dehydrogenated to give thephenylethene monomer.CHHCH32 Restructuring of chloroethene to make poly(chloroethene)i.e., polyvinylchloridePropene molecules combine to formpolypropene.● Most polypropene is produced as amonopolymer (a polymer formedfrom propene only).3 FormingpolyphenyletheneHCCH3 H●Chloroethene molecules combine toform polychloroethene.● 1,2-dichloroethane is made bychlorinating ethene.
This product isthen cracked to form chloroethene.CH3CHMon om ers are the basic units fromwhich a polymer is made.● The systematic name for a polym er isderived from the name of themonomer. For example, polypropeneis “poly” (for polymer) + the alken epropene.● The diagrams at right illustrate theformation of some alkene polymers.●1 Forming polypropeneHCCHHCHHC6 H5HCCHHC6 H5 HC6 H5 HC6 H5 HCCCCCCHHHHHHH4 Poly(tetrafluoroethene)FFCFFFCCFFCFFCFFFFFFFFCCCCCCFFFFFFCF161Key wordsmonomerpolymerpolymerizationCCHCNCHEMISTRY OF CARBONPolymers●HHHOCH3CCHHCCFCH3FFHFHOC6 H5CCHHCCHClHHCCHCH3HHCCHHHStructure of monomerPolymers: table ofproperties and structureMost polym ers have common namesthat are used in everyday language.● The uses of polymers depend on theirproperties.There are several ways in whichpolymers can be classified.● Heat.
Thermoplastics soften whenheated and harden on cooling, so theycan be reshaped many times withoutchanging their chemical structure.Thermosets are chemically altered onheating and produce a permanentlyhard material that cannot be softenedby heating.● Method of polymerization. Additionpolymers are usually formed fromm on om ers containing a –CH=CH- unitto which different atoms or groups areattached.
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