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Unformatted text preview: . Chapter 17: Carboxylic Acids Solutions 374 CHAPTER 17 Solutions to the Problems Problem L7.1 Each of these carboxylic acids has a well-recognized common name. A derivative of glyceric acid is an intermediate in olyco1ysis. Maleic acid is an intennecliate in the tricarboxylic acid (TCA) cycle. Mevalonic acid is an intermediate in the biosynthesis of steroids. Write the 1UPAC name for ea~h compound. Be certain to specify configuration. HQ ~H3 (COOH HO/'yGOOH (a) (b) (c) ~GOOH- OH HO GOOH Mevalonic acid GlyceriC'acid Maleic acid (R)-3,S-Dihydroxy-3- methylpentanoic acid (R)-2,3Dihydroxy- (Z)-2-Butenedioic acid propanoic acid Problem 17.2 Which is the stronger acid in each parr? or or ~GOOH (a) GH:3 GOOH (b) Methanesulfonic Acetic acid acid 2-0xopropanoic acid Propanoic acid . (pyruvic acid) pK a = 4.8 pK a =-1.8 . pKa = 2.S pK a = 4.8 In (a), the third oxygen atom on sulfur increases acidity by both inductive and resonance effects compared to tbe carboxylic acid. I'n (b), the electron withdrawing carbonyl group in the 2 position of pyruvic acid increases acidity due to inductive effects. . P;obl~m 17.3 Write equations for the reaction of each acid in Example 17.3 with ammonia, and name the carboxylic saJ.t . formed. ~COO- NH~ (a) ~COOH- Ammonium butanoate Butanoic acid 9H 9H (b) + NH:J - ~COO- NH: ~COOH Ammonium (S)-lactate (S)-Lactic acid Problem 17.4 Complete the equation for each Fischer esterification. o o (aj 'i'oH + HoD ~H+~'i'o-Q o f-;lO . II (b) ~OH- (a cyclic ester) Chapter 17: Functional Derivatives of Carboxylic Acids Solutions 375 rcl1lem 17,5. Complete the equation for each reaction. o ex. II GOOH (a) \" __ '1. ,eCI + + SOCI 50 2 + HCI 2 ~. OGH ~ OCH 3 oc 3 ('y. . CI+ V 50 2 + HCI (b) Problem 17,6 Account for the observation that the following ~-ketoacid can be heated for extended periods at temperatures above its melting point without noticeable decarboxylation. 930 The mechanism we have proposed for decarboxylation of a ~-ketoacid involves formation of an enol . intermediate and equilibrium of the enol, via keto-enol tautomerism, with the keto form. Given the geOmetry of a bicycloalkane, it is not possible to have a carbon-carbon double bond to a bridgehead carbon because of the prohibitively high angle strain. Therefore, because the enol intermediate cannot be fornied, this ~-ketoacid does not undergo thermal decarboxylation. Side view Because of tbe geometry ~ of the bicyclic ring, it is . not possible to have a . ~ double bond to a . ~ bridgehead carbon atom - . . ' OH This atom would '. .I Top view be too distorted ........::...-; from the ideal 120 Problem 17.7 Write the IUPAC name of each compound, showing stereochemistry where relevant: o-COOH OH (c) ~GOOH (a) (b) ~GOOH....
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