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Dolbier HW Solutions 433 - 19.26 Dicarboxylic acids in...

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Another possibility is the following structure; it also has a center of symmetry and an anti re- lationship between the two carbonyls. Other centrosymmetric structures can be drawn; these have the two hydrogen atoms out of the plane of the carboxyl groups, however, and are less likely to occur, in view of the known pla- narity of carboxyl groups. Structures in which the carbonyl groups are syn to each other do not have a center of symmetry. ( c ) The anion formed on dissociation of o -hydroxybenzoic acid can be stabilized by an intra- molecular hydrogen bond. ( d ) Ascorbic acid is relatively acidic because ionization of its enolic hydroxyl at C-3 gives an anion that is stabilized by resonance in much the same way as a carboxylate ion; the negative charge is shared by two oxygens.
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Unformatted text preview: 19.26 Dicarboxylic acids in which both carboxyl groups are attached to the same carbon undergo ready thermal decarboxylation to produce the enol form of an acid. This enol yields a mixture of cis- and trans-3-chlorocyclobutanecarboxylic acid. The two products are stereoisomers. 1 C OH OH Cl CO 2 H H H Cl HO 2 C H H Cl cis-3-Chlorocyclobutane-carboxylic acid trans-3-Chlorocyclobutane-carboxylic acid 1 CO 2 C OH OH Cl heat C C Cl O O O OH H Compound A Acidic proton in ascorbic acid OH HO O O O NaHCO 3 O OH O 2 OH O O 2 HOCH 2 OH H HOCH 2 OH H HOCH 2 OH H O O C O H O 2 o-Hydroxybenzoate ion (stabilized by hydrogen bonding) O OCH 3 o-Methoxybenzoate ion (hydrogen bonding is not possible) C O 2 C H C H O O O O CARBOXYLIC ACIDS 527 __ __ __...
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