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Molecular Representations
Review of Concepts
Fill in the blanks below. To verify that your answers are correct, look in your textbook at
the end of Chapter 2. Each of the sentences below appears verbatim in the section
entitled Review of Concepts and Vocabulary.
• In bond-line structures, _______atoms and most ________ atoms are not drawn.
• A ________________ is a characteristic group of atoms/bonds that show a
predictable behavior.
• When a carbon atom bears either a positive charge or a negative charge, it will
have ___________, rather than four, bonds.
• In bond-line structures, a wedge represents a group coming ______ the page,
while a dash represents a group _________ the page.
• ___________ arrows are tools for drawing resonance structures.
• When drawing curved arrows for resonance structures, avoid breaking a _______
bond and never exceed _____________ for second-row elements.
• There are three rules for identifying significant resonance structures:
1. Minimize ____________.
2. Electronegative atoms can bear a positive charge, but only if they possess
an ________ of electrons.
3. Avoid drawing a resonance structure in which two carbon atoms bear
_____________ charges.
• A ______________ lone pair participates in resonance and is said to occupy a
____ orbital.
• A _____________ lone pair does not participate in resonance.
Review of Skills
Fill in the blanks and empty boxes below. To verify that your answers are correct, look
in your textbook at the end of Chapter 2. The answers appear in the section entitled
SkillBuilder Review.
SkillBuilder 2.1 Converting Between Different Drawing Styles
(CH3)3COCH3
DRAW THE LEW IS ST RUCTURE OF T HE FOLLOW ING COMPOUND
CHAPTER 2 17
SkillBuilder 2.2 Reading Bond-Line Structures
N
N
O
Cl
CIRCLE ALL CARBON ATOMS IN THE COMPOUND BELOW DRAW ALL HYDROGEN ATOMS IN T HE COMPOUND BELOW
N
N
O
Cl
SkillBuilder 2.3 Drawing Bond-Line Structures
DRAW A BOND-LINE DRAW ING OF THE F OLLOWING COMPOUND:
H C C O
H
H
O
H
C
H
H
C C C
C
H
C
C
H
H
H H
H
H
H
SkillBuilder 2.4 Identifying Lone Pairs on Oxygen Atoms
O O O
AN OXYGEN ATOM
WITH A NEGATIVE
CHARGE WILL HAVE
____ LONE PAIR(S)
AN OXYGEN ATOM
WITH NO FORMAL
CHARGE WILL HAVE
____ LONE PAIR(S)
AN OXYGEN ATOM
WITH A POSITIVE
CHARGE WILL HAVE
____ LONE PAIR(S)
SkillBuilder 2.5 Identifying Lone Pairs on Nitrogen Atoms
N N N
A NITROGEN ATOM
WITH NO FORMAL
CHARGE WILL HAVE
____ LONE PAIR(S)
A NITROGEN ATOM
WITH A POSITIVE
CHARGE WILL HAVE
____ LONE PAIR(S)
A NITROGEN ATOM
WITH A NEGATIVE
CHARGE WILL HAVE
____ LONE PAIR(S)
SkillBuilder 2.6 Identifying Valid Resonance Arrows
RULE 1: THE TAIL OF A CURVED ARROW
CANNOT BE PLACED ON A ______________
RULE 2: THE HEAD OF A CURVED ARROW
CANNOT RESULT IN _____________________
________________________________________
TAIL HEAD
SkillBuilder 2.7 Assigning Formal Charges in Resonance Structures
O O
INDICATE THE LOCATION OF THE NEGATIVE CHARGE IN THE SECOND RESONANCE STRUCTURE BELOW
SkillBuilder 2.8 Drawing Significant Resonance Structures
18 CHAPTER 2
O O H O O H O O H O O H
IDENTIFY WHICH RESONANCE STRUCTURES BELOW ARE SIGNIFICANT AND WHICH ARE INSIGNIFICANT
SkillBuilder 2.9 Identifying Localized and Delocalized Lone Pairs
NH2
O
NH2
O
IDENTIFY WHETHER THE LONE PAIR ON THE
NITROGEN ATOM BELOW IS DELOCALIZED
IDENTIFY THE HYBRIDIZATION STATE
OF THE NITROGEN ATOM
Solutions
2.1.
a)
C C
O
H H
H C C
C
C
H
H
H
H
H
H
H
H
H b)
H C C C
C
C
H
H H
H
O H
H
C H
H
C H
H
H H
H
H H c)
C C C O
C
C
H
H H
H
H
H
H C
H
H C
H
H H
H
H H
H
d)
C C
C
C H
C
C
H
H
H H
H
H
H
H
H
H H e)
C
O
H
C C
C
C
H
H
H
H
H
H
H
H
H
H
C C
H
H
H f)
C C
C
H C
C H
H
C H
H
H H
H
H H
H
H
g)
C C C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
H
H
O H
h)
C C C
H
H
C
H
H
H
H
H
H
H
C C H
H H
H H
i)
C C C
H
H
H
H
H
H
H
O C H
H
H
j)
H C O
C
H C
C H
H
C H
H
C H
H
C H
H
H H
H
H H
H
k)
H C C O
C
C
H
H H
C H
H
C H
H
H H
H
H H
C
H
H
H
l)
H C C O
C
C
H
H H
H H
H
H H
H
CHAPTER 2 19
2.2
(CH3
)3COCH3
and (CH3
)2CHOCH2CH3
2.3 Six
2.4 H2C=CHCH3
2.5.
a)
C C
C
C
C
C
C C
H
H
H
H
H
H
H
H
H
H
H
H H
H
b)
C
C C
N
C
C
H
O H H
H
H H H H
H
H H
c)
C
C
C
C
C
C
H
H H
H
H
H
H
H
H
H
H
H
H
H
d)
C
C
C
C
C
C
CH3
H3C
H3C
CH3
CH3
CH3
e)
C C
C
C
C
C
O
OH
H H
H
H
H
H H
H
H
f)
C
C
C
C
C
C
O
H
H
H
H
H
H
H
H
H H
g)
C
C
C
C
C
C
O
H
H
H
H
H
H
H H h)
C
C
C
C
C
C
OH
H
H
H
H
H
i)
C
H
C
C
C
C
H
H
H
H C
C
H
H
H
H
H
H
H
j)
C
C
C
C
C
C
H H
H
H H
H H
H
H H
k)
C C
C
O
C
C
C
C
H H
H
H
H H
H H
H
H H
H l)
C
H2
C
H2C
C
H2
C
H2
CH2
C
O
2.6
a) decrease (76) b) no change (88)
c) no change (88) d) increase (57)
2.7
a) increase (1214) b) decrease (86)
2.8.
a) b)
O
c)
OH
OH
OH
d)
20 CHAPTER 2
e) f)
OH
g)
OH
h) O
i) j) O
k)
NH2
l)
O
m) n)
Cl
o) p) O
q)
OH
r)
O
O
2.9.
2.10.
a) O
H
Br
δ+
δ+
b) O
O
δ+
δ+
c) Cl
O
δ+
δ+
2.11.
O
amine OH
N
O O
H
N
HO O
O
N
H
NH2
O
alcohol
ether
aromatic amide
amine
carboxylic acid
ester
aromatic
amide
2.12.
a) N
b) No charge c)
N
d) No charge
CHAPTER 2 21
2.13.
a)
O
b)
O
c) No charge d)
H
O
H
H
2.14.
a)
O
b) O
O
c)
OH
O
d)
O
O
e)
O
f)
O
g)
O
H
h) H
O
H
H
i)
O
O
O
j)
O
O
H
H
R
2.15. There are no hydrogen atoms attached to the central carbon atom. The carbon
atom has four valence electron. Two valence electrons are being used to form bonds, and
the remaining two electrons are a lone pair. This carbon atom is using the appropriate
number of valence electrons.
2.16.
a)
N
b)
N
H c)
N
d) no lone pairs
e)
N
f)
N
g) no lone pairs h)
N
H NH2
2.17.
a)
N
O
H
b)
O C N
c)
O O N
d)
N
O O
e) NH2
O
f)
O C N
2.18.
a) one b) zero c) one d) five
22 CHAPTER 2
2.19 Five lone pairs:
O
O
R
NH3
2.20
a)
Troglitazone
S
N
O
O
H
O
O
HO
S
N
O
O
H
O
S
N
O
O
H
O
N
N
N
Rosiglitazone Pioglitazone
b) Yes, it contains the likely pharmacophore highlighted above.
2.21
a) Violates second rule by giving a fifth bond to a nitrogen atom.
b) Does not violate either rule.
c) Violates second rule by giving five bonds to a carbon atom.
d) Violates second rule by giving three bonds and two lone pairs to an oxygen atom.
e) Violates second rule by giving five bonds to a carbon atom.
f) Violates second rule by giving five bonds to a carbon atom.
g) Violates second rule by giving five bonds to a carbon atom, and violates second rule
by breaking a single bond.
h) Violates second rule by giving five bonds to a carbon atom, and violates second rule
by breaking a single bond.
i) Does not violate either rule.
j) Does not violate either rule.
k) Violates second rule by giving five bonds to a carbon atom.
l) Violates second rule by giving five bonds to a carbon atom.
2.22.
O
2.23.
a) b)
CHAPTER 2 23
c)
O
O
O
O
d)
N N
e)
OH OH
f)
N
O O
N
O O
g)
N
O O
N
O O
h)
O O
2.24.
a)
O O
b)
O O
c)
N
O
N
O
b)
2.25.
a)
O
O
O
O
b)
c)
O O
d)
NH2 NH2
24 CHAPTER 2
e)
N
O O
N
O O
f)
O O
g)
O
N
O
O
N
O
h)
H2N
O
OH
O
H2N
O
OH
O
2.26.
a) b)
c)
d)
CHAPTER 2 25
2.27.
a)
N N
b)
N N
c)
O O
2.28.
a)
N N
b)
O O
c)
O O
2.29.
OH
O
OH
O
2.30.
O O
26 CHAPTER 2
2.31.
H2N
HO OH
H2N
HO OH
2.32.
a)
O O O
b)
c)
d)
O
O
O
O
O
O
e)
O O
f)
O
H
O
H
O
H
O
H
O
H
CHAPTER 2 27
g)
N N
h)
N N N
i)
N N
j)
Cl
O
Cl
O
Cl
O
2.33.
a)
N
H
N
H
N
H
b)
N N N
c)
N N
d)
O C N O C N O C N
28 CHAPTER 2
e)
S
O
S
O
f)
g)
O O O
h)
i)
O O
j)
C
N
C
N
k)
C
N
C
N
C
N
l)
OH OH
CHAPTER 2 29
2.34.
O
δ+
δ+ δ+ δ+
δ+ δ+
2.35.
OH δ-
δδ-
δδ-
2.36.
a)
N
H N
H
H
H
delocalized
sp2
hybridized
trigonal planar
localized
sp3
hybridized
trigonal pyramidal
b)
O N
O
One of these lone pairs is
delocalized. The oxygen
atom is therefore sp2
hybridized and has bent
geometry.
localized
sp2
hybridized
geometry not relevant
(connected to only one atom)
delocalized
sp2
hybridized
trigonal planar
c)
localized
sp2
hybridized
geometry not relevant
(connected to only one atom)
delocalized
sp2
hybridized
trigonal planar
O OH
H2N NH2
localized
sp3
hybridized
trigonal pyramidal
One of these lone pairs is
delocalized. The oxygen
atom is therefore sp2
hybridized and has bent
geometry.
d)
N
localized
sp2
hybridized
bent
e)
N
H
delocalized
sp2
hybridized
trigonal planar
30 CHAPTER 2
f)
localized
sp2
hybridized
geometry not relevant
(connected to only one atom)
localized
sp3
hybridized
bent
O
O
O
One of these lone pairs is
delocalized. The oxygen
atom is sp2
hybridized
and has bent geometry.
2.37. Both lone pairs are localized and, therefore, both are expected to be reactive.
2.38.
localized
(not participating in resonance)
N
N
O
NH2
H
localized
(not participating in resonance)
delocalized
(participating in resonance)
localized
(not participating in resonance)
2.39.
C
C
C
C
C
C
C
O OH
O
C
C
O
H
H
H
H
H
H H
C
C
C
C
C
C
HO
N
C
C
O
H
H
H H H
H
H
H
N
C
N
C
C
N
C
C N
O
C
O C
H
H H
H
H H
H
H
H
H
2.40.
2.41.
2.42.
Vitamin A
Vitamin C
OH
O O
HO OH
HO
HO
CHAPTER 2 31
2.43. Twelve (each oxygen atom has two lone pairs)
2.44.
O
N
N O
O N
2.45.
O O O
O O
2.46.
a)
C4H10
C6H14
C8H18
C12H26
In each of the compounds above, the number of hydrogen atoms is equal to two
times the number of carbon atoms, plus two.
b)
C4H8
C7H14
C7H14
C12H24
In each of the compounds above, the number of hydrogen atoms is two times the
number of carbon atoms.
32 CHAPTER 2
c)
C6H10
C9H16 C9H16
C7H12
In each of the compounds above, the number of hydrogen atoms is two times the
number carbon atoms, minus two.
d) A compound with molecular formula C24H48 must have either one double bond or one
ring. It cannot have a triple bond, but it may have a double bond.
e)
2.47.
a) an sp
2
hybridized atomic orbital
b) a p orbital
c) a p orbital
2.48.
a)
N
OH
H
N
OH
H
N
OH
H
b)
O O O
c)
2.49.
a) (CH3)3CCH2CH2CH(CH3)2
b) (CH3)2CHCH2CH2CH2OH
c) CH3CH2CH=C(CH2CH3)2
CHAPTER 2 33
2.50.
a) C9H20
b) C6H14O
c) C8H16
2.51.
(d) is not a valid resonance structure, because it violates the octet rule. The nitrogen atom
has five bonds in this drawing, which is not possible, because the nitrogen atom only has
four orbitals with which it can form bonds.
2.52. 15 carbon atoms and 18 hydrogen atoms:
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
H
H H
H
H
H
H H
H H
H H
H
H H
H
H H
2.53.
O N N N
a) b) c) d)
O
2.54.
Cl
Cl
Cl
Cl
2.55.
a)
O O
b)
O O
c) d)
N N
34 CHAPTER 2
e)
N
H
N
H
N
H
N
H
N
H H H H H H
f)
g)
O O O O
O O O
h)
O
O
O
O
O
O
CHAPTER 2 35
i)
OH OH OH
OH
j)
O O O
O O
2.56. These structures do not differ in their connectivity of atoms. They differ only in
the placement of electrons, and are therefore resonance structures.
2.57.
a) constitutional isomers
b) same compound
c) different compounds that are not isomeric
d) constitutional isomers
2.58.
a) b)
OH
c)
O
d) O
O
e)
Br
