Answers and Explanations

DISCRETE PRACTICE QUESTIONS

1 . D

One mole    of  aldehyde    reacts  with    one mole    of  alcohol via a   nucleophilic    addition    reaction    to

form    a   product called  a   hemiacetal. In  a   hemiacetal, an  –OH group,  an  –OR group,  a   hydrogen

atom,   and an  –R  group   are attached    to  the same    carbon  atom.

2 . B

Tautomerization is  the interconversion of  two isomers in  which   a   hydrogen    and a   double  bond

are moved.  The keto    and enol    tautomers   of  aldehydes   and ketones are common  examples    of

tautomers   seen    on  Test    Day.    Note    that    the equilibrium lies    to  the left    because the keto    form    is

more    stable. Esterification, choice  (A),    is  the formation   of  esters  from    carboxylic  acids   and

alcohols.   Elimination,    choice  (C),    is  a   reaction    in  which   a   part    of  a   reactant    is  removed and a   new

multiple    bond    is  introduced. Dehydration,    choice  (D),    is  a   reaction    in  which   a   molecule    of  water   is

eliminated.

3 . D
The reactions listed in the answer choices are examples of aldol condensations. In the presence
of a base, the α-hydrogen is abstracted from an aldehyde, forming an enolate ion, [CH 3 CHCHO]–.
This enolate ion then attacks the carbonyl group of the other aldehyde molecule, CH 3 CH 2 CHO,
forming the pictured aldol.