Answers to Concept Checks

8.1

Carboxylic  acids   are particularly    acidic  due to  the electron-withdrawing    oxygen  atoms   in  the

functional  group   and the high    stability   of  the carboxylate anion,  which   is  resonance   stabilized  by

delocalization  with    two electronegative oxygen  atoms.

A   dicarboxylic    acid    would   be  the most    acidic, as  the second  carboxyl    group   is  electron-

withdrawing and therefore   contributes to  even    higher  stability   of  the anion   after   loss    of  the first

hydrogen.   However,    a   monocarboxylic  acid    is  more    acidic  than    a   deprotonated    dicarboxylic    acid

because the carboxylate anion   is  electron-donating   and destabilizes    the product of  the second

deprotonation   step,   resulting   in  decreased   acidity.

Electron-withdrawing    substituents    make    the anion   more    stable  and therefore   increase    acidity.

Electron-donating   substituents,   on  the other   hand,   destabilize the anion,  causing the carboxylic

acid    to  be  less    acidic. The closer  the substituent is  to  the carboxylic  acid    on  the molecule,   the

stronger    the effect  will    be.

8.2

Carboxylic  Acid    Derivative Formed   by  Reaction    with: Name  of  Cyclic  Form:

Amide Ammonia   (NH 3 ) or  an  amine Lactam

Ester Alcohol Lactone

Anhydride Another   carboxylic  acid Anhydride

Nucleophilic    acyl    substitution    is  the substitution    of  an  attacking   nucleophile for the leaving

group   of  an  acyl    compound,   which   includes    carboxylic  acids,  amides, esters, and anhydrides. The

nucleophile attacks,    opening the carbonyl    and forming a   tetrahedral intermediate.   The carbonyl

then    reforms,    kicking off the leaving group.  This    reaction    is  favored by  acidic  or  basic   conditions.

Sodium  borohydride is  not strong  enough  to  reduce  carboxylic  acids.  Lithium aluminum

hydride,    however,    is  strong  enough, and reduces carboxylic  acids   to  primary alcohols.

1,3-dicarboxylic    acids   will    spontaneously   decarboxylate   when    heated, due to  the stable  cyclic