Chapter20CarboxylicAcidsCarboxylicacidsarethemostacidicofthecommonorganicfunctionalgroups.ThefunctionalgroupofcarboxylicacidsconsistsofaC=Owith-OHbondedtothesamecarbon.Carboxylgroupisusuallywritten-COOH.Aliphaticacidshaveanalkylgroupbondedto-COOH.Aromaticacidshaveanarylgroup.Fattyacidsarelong-chainaliphaticacids§20.1CarboxylicAcidNomenclatureNamingCyclicAcidsDicarboxylicAcidsTheprincipalgroupisassignedaccordingtothefollowingpriorities:Manyaliphaticacidshavehistoricalnames.PositionsofsubstituentsonthechainarelabeledwithGreekletters.名称§20.2PhysicalProperties低级脂肪酸-液体,溶于水,刺鼻气味。中级脂肪酸-液体,部分溶于水,难闻气味。高级脂肪酸-固体,不溶于水,无味。芳香酸-固体，在水中溶解度不大。大多数羧酸在固态和液体是以二缔合体形式存在。Intermolecularhydrogenbondingbetweentwocarboxylicacidmolecules.Aceticacid,b.p.118C羧酸熔点的变化规律是随羧酸碳原子数增加呈锯齿形上升。偶数碳原子的羧酸比它前后相邻的两个同系物的熔点为高。§20.3SpectroscopicAnalysisIRSpectroscopyChenliChenliResonance(ppm)NMRSpectroscopyMassSpectrometryPeakforthemolecularion,M+,isusuallyprominent.FragmentsduetolossofOH(M-17)+andthenlossofCO(M-45)+MassSpectrometry§20.4StructureandBondingThereislowelectrondensity(blue)onHatomofthe-CO2Hgroupalcohol,i.e.H+character.TheHatomoftheRCO2Hisacidic(pKa~5).Themostimportantreactionsofcarboxylicacidsconvertsthemintocarboxylicacidderivativessuchasacylhalides,estersandamidesviaencephalicacylsubstitutionreactions.ChenliX-光衍射证明甲酸盐的两个碳氧键长一样，没有双键与单键的差别;而甲酸的C=O键长与C-O键长不一样，说明两个碳氧键是不一样.§20.5AcidityofCarboxylicAcidsCarboxylicAcidTheinductiveeffectofthecarbonylgroupTheresonanceeffectofthecarbonylgroup§20.6.1SubstituentsandAcidStrengthChenliCarboxylicAcidCarboxylicAcidChenli§20.6.2SaltofCarboxylicAcidsNamingAcidSaltsUsuallysolidswithnoodor.CarboxylatesaltsofNa+,K+,Li+,andNH4+aresolubleinwater.Soapisthesolublesodiumsaltofalongchainfattyacid.SaltscanbeformedbythereactionofanacidwithNaHCO3,releasingCO2.羧酸的钠盐和钾盐不溶于非极性溶剂，一般少于10个碳原子的一元羧酸的钠盐和钾盐能溶于水（10～18个碳原子羧酸的钠盐或钾盐在水中形成胶体溶液）。Detergents(清洁剂)aresubstances,includingsoaps,thatcleansebymicelles(胶束)action.PurifyinganAcid利用羧酸的酸性和羧酸盐的性质，可以把它与中性或碱性化合物分离§20.6.3Ioniz