Answers and Explanations

DISCRETE PRACTICE QUESTIONS

1 . D

This    compound    is  a   β-keto  acid:   a   carbonyl    functional  group   at  the β-position  from    a   carboxyl

group.  Decarboxylation occurs  with    β-keto  acids   and β-dicarboxylic  acids   because they    can form    a

cyclic  transition  state   that    permits simultaneous    hydrogen    transfer    and loss    of  carbon  dioxide.

Choice  (B) is  a   diketone    and does    not have    a   single  carboxyl    group.  Choices (A) and (C) are γ-  and

δ-dicarboxylic  acids,  respectively,   and can decarboxylate   but with    more    difficulty.

2 . D
The boiling points of compounds depend on the strength of the attractive forces between
molecules. In both alcohols and carboxylic acids, the major form of intermolecular attraction is
hydrogen bonding; however, hydrogen bonding is much stronger in carboxylic acids as compared
to alcohols because carboxylic acids are more polar and the carbonyl also contributes to
hydrogen bonding in addition to the hydroxyl group. The stronger hydrogen bonds elevate the
boiling points of carboxylic acids compared to alcohols. Boiling points also depend on molecular
weight, choice (A), but in this case, the difference in molecular weight is insignificant compared
to the effect of hydrogen bonding. Choices (B) and (C) are both true but do not explain the
difference in boiling points.

3 . B
The acidity of carboxylic acids is significantly increased by the presence of highly electronegative
functional groups. Their electron-withdrawing effect increases the stability of the carboxylate
anion, favoring proton dissociation. This effect increases as the number of electronegative
groups on the chain increases, and it also increases as the distance between the acid functionality
and electronegative group decreases. This answer has two halogens bonded to it at a smaller
distance from the carboxyl group compared to the other answers.

4 . C