Chemistry - an illustrated guide to science (794128), страница 28
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On polym erization , one ofthe carbon–carbon bonds becomes abond to another unit. Condensationpolymers are formed fromcondensation reactions in which asmall molecule, sometimes but notalways water, is lost.● Formula. Homopolymers are formedfrom one monomer unit. Co-polymersare formed from two or moremonomers.● Chemical structure. Linear chains mayhave straight, zigzag, coiled, orrandom spatial arrangements.Branched chains have side branchchains attached to the main chains.Cross-linked chains have two or threedimensional cross-linkage betweenchains.● Steric structure. Isotactic: in which allside groups are on the same side ofthe main chain.
Syndiotactic: in whicheach alternative side group has thesame orientation. Atactic: in whichthere is no specific pattern to thedistribution of side groups.brittle but cheaplow friction and stable to heattransparentstrong fibersPolystyrenePTFE(polytetrafluoroethene)PerspexAcrilanPoly(phenylethene)Poly(ethene)Poly(methyl-2-methylpropenoate)Poly(propenenitrile)© Diagram Visual Information Ltd.plastic toys, expanded withair and used for insulationflexiblePVC (polyvinylchloride)Poly(chloroethene)wool substitute in textilescoating fabrics and insulationon wires and cablessubstitute for glassmolding rigid articles,film and fibershigh densityPolypropylenePoly(propane)non-stick coating on pansfilm and bags;molding rigid articleslow density;high densityPolyethene●Poly(ethene)Polymer systematic namePolymer common namePropertiesUsesClassification162CHEMISTRY OF CARBONKey wordsalcoholalkenecarboxylic acidesterfunctional grouphomologousseriesoxidationFunctional groups andhomologous seriesFunctional group1 AlkenesPropeneHFunctional groupsA fu n ction al grou p is the atom orgroup of atoms present in a moleculethat determines the characteristicproperties of the molecule.● A hom ologou s series is a group ofcompounds that contain the samefunctional group.
The physicalproperties of a homologous seriesshow a gradation as molecular sizeincreases. The chemical properties of ahomologous series are similar becausethey are determined by the functionalgroup.ExampleH●CC CH2 AlcoholsHEthanolH HC OH C C OAlken es contain the functional groupC=C.● Their general formula is CnH2n.● Alkenes are reactive and undergoadditional reactions.H●3 Carboxylic acidsAlcohols contain the functional groupC-OH.● Their general formula is CnH2n+1OH.● Alcohols can also undergo oxidationto give carboxylic acids, or they can bedehydrated to alkenes. They can alsoreact to form ester compounds●H HHEthanoic acidOOHCO H3 Carboxylic acidsCarboxylic acids contain thefunctional group -COOH.● Carboxylic acids are typically weak acidsthat partially dissociate into H+ cationsand RCOO- anions in aqueous solution.● Carboxylic acids are widespread innature.C CH1 Alkenes2 AlcoholsHCCHO HH© Diagram Visual Information Ltd.●4 EstersEsters contain the functional group–COOC- .● Esters are formed by a reactionbetween a carboxylic acid and analcohol.● Esters are used in flavorings andperfumes.●Methylethanoate4 EstersOHCH C CHHO C HO HOH163AlcoholsCHEMISTRY OF CARBON1 The first six alcoholsKey wordsStructureNameCH3-OHmethanolCH3CH2 -OHethanolCH3CH2 CH2 -OHpropan-1-olCH3CH2 CH2 CH2-OHbutan-1-olCH3CH2 CH2 CH2CH2-OHpentan-1-olCH3CH2 CH2 CH2CH2CH2-OHhexan-1-olalcoholalkanefunctional grouphydrogen bond1 Naming●2 ClassificationHCCHHOHHPrimary alcoholHHHCCCHOH HH H HHHHHSecondary alcoholCCCHOH HTertiary alcohol2 Classification●H3 Sharing of electrons●3 Sharing of electronsRO!H!+4 Hydrogen bondingROAn oxygen atom is moreelectronegative than a hydrogen atom,and this leads to an unequal sharing ofthe electrons in the O-H bond.
Thebonding electrons are drawn moretoward the oxygen atom and, becausethe electrons carry a negative charge,the oxygen atom becomes slightlynegative. This is described as deltaminus and is denoted by !- .Conversely, the hydrogen atombecomes slightly positive—delta plus,denoted by !+ . ( R represents thecarbon group attached to the oxygen.)4 Hydrogen bonding●HOHAlcohols may be classified as primary,secondary, or tertiary on the basis ofthe number of carbon atoms bondedto the carbon carrying the fu n ction algrou p ( -OH).RThe -OH functional group generallymakes the alcohol molecule polar.
Ithas a positive charge at one end and anegative at the other. Molecules canform hydrogen bon ds with oneanother and other compounds whenthe oppositely charged parts areattracted to each other, forminghydrogen bonds.© Diagram Visual Information Ltd.HHHAlcohols are named by dropping theterminal “e” from the alkan e chainand adding “ol.” For example,methane is the alkane; methanol is thealkanol, or alcohol. When necessary,the position of the hydroxyl ( -OH)group is indicated by a numberbetween the alkane name and the “ol,”e.g., propan-1-ol, or in front of thename, e.g., 2-propanol.164CHEMISTRY OF CARBON1 The first six carboxylic acidsKey wordsalkalicarbonatecarboxylic aciddissociationhomologousseriespHsalt1 Naming●Carboxylic acidsCarboxylic acids are named by addingthe suffix “anoic acid” to the prefixesused for all hom ologou s series oforganic compounds.
For example, thecarboxylic acid containing threecarbon atoms is “prop” + “anoic acid”= “propanoic acid.”StructureNameCHOOHmethanoic acidCH3COOHethanoic acidCH3CH2COOHpropanoic acidCH3CH2CH2COOHbutanoic acidCH3CH2CH2CH2COOHpentanoic acidCH3CH2CH2CH2CH2COOHhexanoic acid2 Hydrogen bonding2 Hydrogen bonding●Hydrogen bonding is present betweencarboxylic acid molecules, resulting inhigher boiling points than mightotherwise be expected and miscibilitywith water.OR3 IonizationRCCCarboxylic acids ionize to givehydrogen ions, H+ ; however, they areweak acids because they are onlypartially ionized.● The dissociation constant for ethanoicacid, for example, is 1.75 x 10-5mol3dm -6.
This means that only about4 molecules in every 1,000 are ionizedat any one time.O●CharacteristicsCarboxylic acids have a pH value ofapproximately 3–5.● Carboxylic acids react with carbon atesand hydrogencarbonates to producecarbon dioxide:●2H+ (aq) + CO32- (aq) ➞H2O(l) + CO2(g)H+ (aq) + HCO3- (aq) ➞H2O(l) + CO2(g)© Diagram Visual Information Ltd.●Carboxylic acids form salts withalkalis:CH3COOH(aq) + NaOH(aq) ➞ethanoic acidsodium hydroxideCH3COO- Na+ (aq) + H2O(l)sodium ethanoate waterOHOH3 IonizationORCOROCO + H165EstersCHEMISTRY OF CARBONKey words1 Forming estersconcentratedsulfuricacidORCOH + HOR´alcoholalkylarylcarboncarboxylic acidORCH2 OR´OEsters2 Naming●Structure of esterHHCName of esterEsters are formed by the reaction ofcarboxylic acids with alcohols in thepresence of a strong acid catalyst, suchas concentrated sulfuric acid.
Thereaction involves the loss of water.● Esters generally have a fruity smell thatcan be used to identify their presence.They are used for food flavorings andin cosmetics.● Esters have no –OH group, so theycannot form hydrogen bond likecarboxylic acids and alcohols.Consequently, they are more volatileand are insoluble in water.●HCmethyl ethanoateOCHHHCOCOHEsters contain the fu n ction al grou p–COOR, where R is an alkyl or an arylgroup.1 Forming estersOHHesterfunctional groupsaponificationHHCCHHethyl ethanoateH2 NamingHHCCOHHHHCCHHThe name of an ester is derived fromthe carboxylic acid and the alcoholfrom which it is formed.● The alcohol part of an ester is writtenat the beginning of the ester name;from methanol we get methyl, fromethanol we get ethyl, etc.● The acid part of an ester is written atthe end of the ester name.
It is writtenas if it was an ionic carboxylate groupin a salt; from ethanoic acid we getethanoate, from propanoic acid we getpropanoate, etc.●OHClHCCCHHHpropyl ethanoateHOCmethyl propanoateOCH33 SaponificationWhen esters are heated with an alkali,such as sodium hydroxide, they arereadily hydrolyzed to form an alcoholand a carboxylic acid salt.● This may be described as asapon ification reaction. It isimportant in the production of soapsfrom fats and oils.3 SaponificationOROC+ NaOHOR´RC+ R´O– Na+OH© Diagram Visual Information Ltd.●166CHEMISTRY OF CARBON1 Common fatty acidsSoaps are cleansing agents made fromfatty acids derived from natural oilsand fats. Detergen ts are made fromsynthetic chemical compounds.1 Fatty acids●Carboxylic acids occur in animal andplant fats and oils. They may containfrom 7 to 21 carbon atoms and areoften referred to as fatty acids.2 Making soap●Most naturally occurring fats and oilsare esters of propane-1,2,3-triol(glycerine).
When the fats are boiledwith sodium hydroxide, propane1,2,3,triol and a mixture of sodium salts ofthe three carboxylic acids are formed.These salts are what we call soaps.3 Soap molecule●One end of a soap molecule is ionic,while the other end is covalent. Theionic end is described as hydrophilicbecause it dissolves in water.Conversely, the covalent end isdescribed as hydrophobic because itdoes not dissolve in water, but it willdissolve in organic substances like oils.4 Cleaning actionThe cleaning action of soap is theresult of the different affinities of thetwo ends of the soap molecule.● The hydrophobic end of the moleculedissolves in oils and fats on the fabric,while the hydrophilic end of themolecule remains in the water.● The oil and fat particles are lifted offthe fabric and held in the water bysoap molecules.© Diagram Visual Information Ltd.●5 Detergent molecule●Alkylbenzene sulfonates are commonexamples of detergents.Found inpalmitic acidCH3(CH2 ) 14 COOHanimal and vegetable fatsstearic acidCH3(CH2 ) 16 COOHanimal and vegetable fatsoleic acidCH3(CH2 ) 7CH=CH(CH2 ) 7COOHmost fats and oilslinoleic acidCH3(CH2 ) 4 CH=CHCH2 CH=CH(CH2) 7COOHsoya-bean oil and nut oil2 Making soapOOCH2—OH + R´ —C—O–Na+CH2—O—C—R´OOCH —O—C—R´´+ 3NaOHCH —OH + R´´ —C—O–Na+OOCH2—OH + R´´´—C—O–Na+CH2—O—C—R´´´3 Soap moleculeH H H H H H H H H H H H H H HOH—C—C—C—C—C—C—C—C—C—C—C—C—C—C—C—CO–Na+H H H H H H H H H H H H H H H4 Cleaning actionwaterwaterCNaOOOC==OO==●FormulaCONaONaOC==Soaps and DetergentsName==hydrophobicsoap==Key wordscarboxylic aciddetergentesterfatty acidhydrophilicSoaps and detergentsCNaOONaoilfabric5 Detergent moleculeH H H H H H H HOC—CC—S—O–Na+H—C—C—C—C—C—C—C—C—CC==CH H H H H H H HHOH167Organic compounds:statesH HKey wordsalkanealkenehomologousseriesAlkanesH C C HGasPhysical properties●H HH H H H HChainlengthC5 ,AlkanesH C C C C C HLiquidH H H H HH HChainlengthC34 ,H HH C C (CH2) 30 C C HH HHChainlengthC2 ,HChainlengthC34 ,H HLiquidH H HHHC C (CH2) 30 C CHThe simplest alken e is the two carbonalkene, ethene ( C2H4 ), which is a gas.● 2-pentene ( C5 H10 ), which is a fivecarbon alkene, is a liquid.● 2-butedecane, which is a 34 carbonalkene, is a solid.●GasH C C C C C HHAlkenesHH HChainlengthC5 ,The simplest alkan e is CH4 , methane.The next simplest alkane is the twocarbon alkane, ethane ( C2H6 ).
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