chapter4

chapter4 - 4-4-1Organic Organic H BrownWilliam H...

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Unformatted text preview: 4-4-1Organic Organic ChemistryChemistryWilliam H. BrownWilliam H. BrownChristopher S. FooteChristopher S. FooteBrent L. IversonBrent L. Iverson4-4-2Acids Acids and and BasesBasesChapter 4Chapter 44-4-3Arrhenius Acids and BasesArrhenius Acids and Bases◆In 1884, Svante Arrhenius proposed these definitions •acid:acid:a substance that produces H3O+ions aqueous solution•base:base:a substance that produces OH-ions in aqueous solution•this definition of an acid is a slight modification of the original Arrhenius definition, which was that an acid produces H+in aqueous solution•today we know that H+reacts immediately with a water molecule to give a hydronium ionH+(aq)+H2O(l)H3O+( aq)Hydronium ion4-4-4Brønsted-Lowry DefinitionsBrønsted-Lowry Definitions◆Acid:Acid:a proton donor◆Base:Base:a proton acceptor+Proton donor Protonacceptor-OHHOHHOHH++OHH+ProtonacceptorProtondonor+OHHOHHNHHHHHH++NHH::::4-4-5Conjugate Acids & BasesConjugate Acids & Bases•conjugate baseconjugate base:the species formed from an acid when it donates a proton to a base •conjugate acid:conjugate acid:the species formed from a base when it accepts a proton from an acid•acid-base reaction:acid-base reaction:a proton-transfer reaction•conjugate acid-base pair:conjugate acid-base pair:any pair of molecules or ions that can be interconverted by transfer of a protonHCl(aq)H2O( l)Cl-(aq)H3O+(aq)++WaterHydrogenchlorideHydroniumionChlorideion(base)(acid)(conjugateacid of H2O)(conjugatebase of HCl)conjugate acid-base pairconjugate acid-base pair4-4-6Conjugate Acids & BasesConjugate Acids & Bases•Brønsted-Lowry definitions do not require water as a reactant•consider the following reaction between acetic acid and ammoniaNH4+CH3COOHCH3COO-NH3++Acetic acidAmmonia(acid)conjugate acid-base pairAcetate ionAmmoniumion(base)(conjugate baseacetic acid)(conjugate acidof ammonia)conjugate acid-base pair4-4-7Conjugate Acids & BasesConjugate Acids & Bases•we can use curved arrows to show the flow of electrons in an acid-base reaction CH3-C-OOHN HHH CH3-C-O -OH-N-HHH++Acetic acid(proton donor)Acetate ion::::::Ammonia(proton acceptor)Ammoniumion4-4-8Conjugate Acids & BasesConjugate Acids & Bases◆Many organic molecules have two or more sites that can act as proton acceptors◆in this chapter, we limit our discussion to carboxylic acids, esters, and amides◆in these molecules, the favored site of protonation is the one in which the charge is more delocalized◆question: which oxygen of a carboxylic acid is protonated?CH3-C-O-HO+H2SO4CH3-C-O-HHO+CH3-C-O-HHO++ HSO4-orA(protonation on the carbonyl oxygen)B(protonation on thehydroxyl oxygen)4-4-9Conjugate Acids & BasesConjugate Acids & Bases◆for protonation on the carbonyl oxygen, we can write three contributing structures◆two place the positive charge on oxygen, one places it on carbon◆A-1 and A-3 make the greater contribution because all atoms have complete octets◆the positive charge is delocalized over three atoms...
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chapter4 - 4-4-1Organic Organic H BrownWilliam H...

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