有机化学英文课件chapter5

5-5-1 1Organic ChemistryWilliam H.BrownWilliam H.BrownWilliam H.BrownChristopher S.FooteChristopher S.FooteChristopher S.FooteBrent L.IversonBrent L.IversonBrent L.Iverson5-5-2 2Alkenes:Structure andNomenclatureChapter 5Chapter 55-5-3 3Unsaturated HydrocarbonsuuUnsaturated hydrocarbon:Unsaturated hydrocarbon:contains one or more carbon-carbon double or triple bondsuuAlkene:Alkene:contains a carbon-carbon double bond and has the general formula CnH2nuuAlkyne:Alkyne:contains a carbon-carbon triple bond and has the general formula CnH2n-25-5-4 4Unsaturated HydrocarbonsuuArenes:Arenes:benzene and its derivatives(Ch 21-22)we do not study arenes until Chapters 21&22however,we show structural formulas of compounds containing the phenyl group before that timethe phenyl group is not reactive under any of the conditions we describe in Ch 6-205-5-5 5Structure of AlkenesuA double bond consists of one sigma bond formed by the overlap of sp2 hybrid orbitals and one pi bond formed by the overlap of parallel 2p orbitalsthe two carbon atoms of a double bond and the four atoms bonded to them lie in a plane,with bond angles of approximately 1205-5-6 6Structure of Alkenesit takes approximately 264 kJ(63 kcal)/mol to break the pi bond in ethylene;that is,to rotate one carbon by 90 with respect to the other so that there is no overlap between 2p orbitals on adjacent carbons5-5-7 7Cis,Trans Isomerism in AlkenesuuCis,transCis,trans isomers:isomers:isomers that have the same connectivity but a different arrangement of their atoms in space due to the presence of either a ring or a carbon-carbon double bond5-5-8 8Index of Hydrogen DeficiencyuuIndex of hydrogen deficiency(IHD):Index of hydrogen deficiency(IHD):the sum of the number of rings and pi bonds in a moleculeuTo determine IHD,compare the number of hydrogens in an unknown compound with the number in a reference hydrocarbon of the same number of carbons and with no rings or pi bondsthe molecular formula of the reference hydrocarbon is CnH2n+25-5-9 9Index of Hydrogen Deficiencyfor each atom of a Group 7 element(F,Cl,Br,I),add one Hno correction is necessary for the addition of atoms of Group 6 elements(O,S)to the reference hydrocarbonfor each atom of a Group 5 element(N,P),subtract one hydrogenIDH=2(Hreference -Hmolecule)5-5-1010Index of Hydrogen DeficiencyProblem:Problem:isopentyl acetate has a molecular formula of C7H14O2.Calculate its IHDreference hydrocarbon C7H16IHD=(16-14)/2=1 Problem:Problem:calculate the IHD for niacin,molecular formula C6H6N2Oreference hydrocarbon C6H16IHD=(16-6)/2=5OOIsopentyl acetate5-5-1111IUPAC Nomenclature1.Number the longest chain of carbon atoms that contains the double bond in the direction that gives the carbons of the double bond the lowest numbers2.Locate the double bond by the number of its first carbon3.Name substituents4.Number the carbon,locate and name substituents,locate the double bond,and name the main chain5-5-1212Common NamesuDespite the precision and universal acceptance of IUPAC nomenclature,some alkenes,particularly low-molecular-weight ones,are known almost exclusively by their common names5-5-1313Common Namesthe common names methylene,vinyl,and allyl are often used to show the presence of the following alkenyl groups5-5-1414The Cis,Trans SystemuConfiguration is determined by the orientation of atoms of the main chain5-5-1515The E,Z Systemuses priority rules(Chapter 3)if groups of higher priority are on the same side,the configuration is Z(German,zusammen)if groups of higher priority are on opposite sides,the configuration is E(German,entgegen)5-5-1616The E,Z SystemuuExample:Example:name each alkene and specify its configuration by the E,Z system5-5-1717Cis,Trans IsomerismuCycloalkenesin small-ring cycloalkenes,the configuration of the double bond is cis these rings are not large enough to accommodate a trans double bond5-5-1818Cis,Trans Isomerismtrans-cyclooctene is the smallest trans cyclooctene that has been prepared in pure form and is stable at room temperaturethe cis isomer is 38 kJ(9.1 kcal)/mol more stable than the trans isomerthe trans isomer is chiral even though it has no chiral center5-5-1919Dienes,Trienes,and PolyenesuFor alkenes containing two or more double bonds,change the infix-enen-to-adienadien-,-atrienatrien-,etc.those containing several double bonds are often referred more generally as polyenesfollowing are three dienes5-5-2020Dienes,Trienes,and Polyenesfor alkenes with n n double bonds,each of which can show cis,trans isomerism,2 2n n stereoisomers are possibleexample:22=4 cis,trans isomers are possible for 2,4-heptadiene5-5-2121Dienes,Trienes,and Polyenesvitamin A,a biologically important compound for which a number of cis,trans isomers is possiblethere are four double bonds about which cis,trans isomerism is possible,for 24=16 stereoisomers5-5-2222Physical PropertiesuAlkenes are nonpolar compoundsuThe only attractive forces between their molecules are dispersion forcesuThe physical properties of alkenes are similar to those of alkanes5-5-2323TerpenesuuTerpene:Terpene:a compound whose carbon skeleton can be divided into two or more units identical with the carbon skeleton of isoprene5-5-2424TerpenesuMyrcene,C10H16,a component of bayberry wax and oils of bay and verbenauMenthol,from peppermint5-5-2525Terpenes-Pinene,from turpentinecamphor,from the camphor tree5-5-2626Fatty AcidsuAnimal fats and vegetable oils are both triesters of glycerol,hence the name triglyceridetriglyceridehydrolysis of a triglyceride in aqueous base followed by acidification gives glycerol and three fatty acidsfatty acids with no C=C double bonds are called saturated fatty acidthose with one or more C=C double bonds are called unsaturated fatty acids5-5-2727Fatty Acidsthe most common fatty acids have an even number of carbons,and between 12 and 20 carbons in an unbranched chainthe C=C double bonds in almost all naturally occurring fatty acids have a cis configurationthe greater degree of unsaturation,the lower the melting pointtriglycerides rich in unsaturated fatty acids are generally liquid at room temperature and are called oilsoilstriglycerides rich in saturated fatty acids are generally semisolids or solids at room temperature and are called fatsfats5-5-2828Fatty Acidsthe four most abundant fatty acids5-5-2929Fatty Acidscarbon chains of saturated fatty acids exist largely in the staggered,anti-conformationbecause of their high degree of order,they pack together well and are held together by dispersion forcesas a result both saturated fatty acids and triglycerides derived from them are solids at room temperaturefollowing is a saturated triglyceride5-5-3030Fatty Acidscis double bonds place kinks in the chains of unsaturated fatty acidsunsaturated fatty acids and the triglycerides derived from them do not pack as well in a crystal lattice as their saturated counterparts,and have weaker dispersion forces between their moleculesbutter fat,for example,has a high content of saturated fatty acids and is a solid at room temperaturesalad oils(from plant oils)have a high content of polyunsaturated fatty acids and are liquid at room temperature5-5-3131Alkenes:Structure andNomenclatureEnd Chapter 5End Chapter 5