Answers and Explanations

DISCRETE PRACTICE QUESTIONS

1 . D

The reactivity  of  the carbonyl    can be  attributed  to  the difference  in  electronegativity   between the

carbon  and oxygen  atoms.  The more    electronegative oxygen  atom    attracts    the bonding electrons

and is  therefore   electron-withdrawing.   Thus,   the carbonyl    carbon  is  electrophilic.  One resonance

structure   of  the carbonyl    pushes  the π   electrons   onto    the oxygen, resulting   in  a   positively  charged

carbonyl    carbon.

2 . B
Assuming the length of the carbon chain remains the same, the alkane consistently has the
lowest boiling point. The boiling point of the ketone is elevated by the dipole in the carbonyl. The
boiling point of the alcohol is elevated further by hydrogen bonding.

3 . C
The reaction between a ketone and one equivalent of alcohol produces a hemiketal. This has an –
OR group, an –OH group, and two alkyl groups attached at the same carbon. Choice (A) is a ketal,
with two –OR groups and two –R groups. Choice (B) is a hemiacetal, with an –OH group, an –OR
group, one R group, and a hydrogen atom (not drawn). Choice (D) is a ketone. Note that a
hemiketal is a very unstable compound, and will react rapidly with a second equivalent of alcohol
to form a ketal in acidic conditions.

4 . A
Aldehydes and ketones react with ammonia and nitrogen-based derivatives to form imines—
compounds with a double bond between carbon and nitrogen.

5 . B
Aldehydes are easily oxidized to the corresponding carboxylic acids by KMnO 4 . In choice (A), the
aldehyde has been reduced to an alcohol. In choice (C), the molecule has not reacted. In choice