Lista de exercícios Teoria Estrutural

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Universidade Federal do Ceará 
Departamento de Química orgânica e inorgânica 
Química Orgânica I 
 Lista de Exercícios- Teoria Estrutural 
 
1) Desenhe quatro estruturas de ressonância e o híbrido de ressonância para o composto a 
seguir. 
 
 
 
 
2) O aleno, H2C=C=CH2, é incomum pelo fato de possuir duas ligações duplas adjacentes. O 
átomo de carbono central possui que hibridação? Desenhe um diagrama de orbitais 
justificando a sua resposta. E quanto à hibridação dos carbonos das extremidades? 
 
3) Qual dos seguintes pares de estruturas a seguir representa formas de ressonância? 
 
 
. 
 
 
 
 
 
 
 
 
 
4) Qual das seguintes substâncias são aromáticas? 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5) O metóxido de sódio, NaOCH3, possui ligações covalentes e iônicas. Identifique na 
molécula cada uma delas. 
 
6) Quais das seguintes moléculas se espera que tenha momento de dipolo zero? 
 
666 Chapter 14 Aromatic Compounds
AROMATICITY
14.18 Which of the following molecules would you expect to be aromatic?
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
(k)
(l) S
!
"
"
!
!
N
"
N
N
N
"
O
"
"
14.19 Use the polygon-and-circle method to draw an orbital diagram for each of the following compounds.
(a) (b)
14.20 Write the structure of the product formed when each of the following compounds reacts with one molar equiva-
lent of HCl.
(a) (b)
14.21 Which of the hydrogen atoms shown below is more acidic? Explain your answer.
A B
14.22 The rings below are joined by a double bond that undergoes cis–trans isomerization much more readily than the
bond of a typical alkene. Provide an explanation.
∆
HH
N
N
H
HCl (1 equiv.)N
N
CH3
HCl (1 equiv.)
!"
solom_c14_632-675hr.qxd 6-10-2009 12:52 Page 666
Exercises 69
2.33 • Which of the fo llowing pairs of st ru ctu res rep resen t reso nan ce forms?
"' 0=1 a (b) :0: : 0 :I a nd 6 6-and
(c) :n: " .." (dl ;0 : :0:6 and 6- 6 and 6-
2.34 . ... Draw as many re so na nce struc ture s as you can fo r the following species :
(a) : 0 :
II "
H3C-C- CH2-
Ib1a:-/H
\ H
H
(c) : NH2.. I +
H2N-C= NH2
.. +
(d)
+
(e) H2C =CH -CH=CH-CH-CH3
2.35 Cyc lob u tad iene is a rec ta ngula r molecul e wit h tw o sho rte r double bond s and
two lo nger single bonds. W hy do the foll owing st ruc tures not repre sen t reso-
na nce for m s?
2.36 Alcohol s ca n act eith er as wea k acids o r as weak ba ses} just as wa te r can . Show
the reac tio n o f methanol, C I-I :lO H}with a strong acid such as HCl an d w ith a
st rong base suc h as Na+ - N 1-I 2 .
2.37 The 0 - H h ydrogen in ac etic acid is m uch more acid ic than an y o f the
C - H h ydr ogens . Explai n th is result using resonance st ruc tu re s,
Acetic acid
2.38 • \1\Ih1ch of th e follo w ing a re likely to act as Lewis acids and wh ich as Lewi s
bases?
(a ) /l lBr:, (b ) GhCI-I2NH2 (c)
(d) H F (e) (f) TiC l4
2.39 Draw an e lec tron -do t st ruc ture fo r eac h o f th e molecul es in Pro b lem 2 .38 , indi -
ea tin g a ny un sha red elec t ro n pa irs.
2.40 • Wr ite the product s of th e foll owing ac id- base reactions:
(a) CH:,OJ-! + H2S0 4 ;::2 ?
(b) CH30 li + <=t ?
(c) Cl-l 1N H3+ C l- + NaO I-l zz: ]
• As sign abl e in OWL Key Idea Probl ems
Section 1.16 An Introduction to Acids and Bases 39
Born in Denmark, Johannes
Nicolaus Brønsted (1879–1947)
studied engineering before he
switched to chemistry. He was a pro-
fessor of chemistry at the University
of Copenhagen. During World War II,
he became known for his anti-Nazi
position, and in 1947 he was elected
to the Danish parliament. He died
before he could take his seat.
The dipole moment of chloromethane is greater (1.87 D) than the dipole
moment of the bond (1.5 D) because the dipoles are oriented so that
they reinforce the dipole of the bond—they are all in the same relative direc-
tion. The dipole moment of water (1.85 D) is greater than the dipole moment of a sin-
gle bond (1.5 D) because the dipoles of the two bonds reinforce each
other. The lone-pair electrons also contribute to the dipole moment. Similarly, the di-
pole moment of ammonia (1.47 D) is greater than the dipole moment of a single
bond (1.3 D).
PROBLEM 24
Account for the difference in the shape and color of the potential maps for ammonia and
the ammonium ion in Section 1.12.
PROBLEM 25!
Which of the following molecules would you expect to have a dipole moment of zero? To
answer parts g and h, you may need to consult your answers to Problem 23 a and b.
a. c. e. g.
b. d. f. h.
1.16 An Introduction to Acids and Bases
Early chemists called any compound that tasted sour an acid (from acidus, Latin for
“sour”). Some familiar acids are citric acid (found in lemons and other citrus fruits),
acetic acid (found in vinegar), and hydrochloric acid (found in stomach acid—the sour
taste associated with vomiting). Compounds that neutralize acids, such as wood ashes
and other plant ashes, were called bases, or alkaline compounds (“ash” in Arabic is al
kalai). Glass cleaners and solutions designed to unclog drains are alkaline solutions.
The definitions of “acid” and “base” that we use now were provided by Brønsted
and Lowry in 1923. In the Brønsted–Lowry definitions, an acid is a species that do-
nates a proton, and a base is a species that accepts a proton. (Remember that positive-
ly charged hydrogen ions are also called protons.) In the following reaction, hydrogen
chloride (HCl) meets the Brønsted–Lowry definition of an acid because it donates a
proton to water. Water meets the definition of a base because it accepts a proton from
HCl. Water can accept a proton because it has two lone pairs. Either lone pair can form
a covalent bond with a proton. In the reverse reaction, is an acid because it do-
nates a proton to and is a base because it accepts a proton from H3O+.Cl-Cl-,
H3O+
BF3H2C“CHBrNH3H2C“O
BeCl2H2C“CH2CH2Cl2CH3CH3
H H
Cl
C
H
H H
H
H
H
O
chloromethane
µ = 1.87 D
water
µ = 1.85 D
ammonia
µ = 1.47 D
N
N¬H
O¬HO¬H
C¬Cl
C¬HC¬Cl
(CH3Cl)
C C Cl
Cl
Cl
Clcarbon dioxideµ = 0 D
carbon tetrachloride
µ = 0 D
OO
Thomas M. Lowry (1874–1936)
was born in England, the son of an
army chaplain. He earned a Ph.D. at
Central Technical College, London
(now Imperial College). He was head
of chemistry at Westminster Training
College and, later, at Guy’s Hospital
in London. In 1920, he became a
professor of chemistry at Cambridge
University.
BRUI01-001_059r4 20-03-2003 2:58 PM Page 39
7) Entre os remédios de venda liberada mais comuns que você poderia encontrar em uma 
farmácia, estão os analgésicos, como ibuprofeno (Advil), naproxeno (Aleve) e 
acetaminofeno (Tylenol). 
a. Quantos átomos de carbono hibridizados sp3 tem cada molécula? 
b. Quantos átomos de carbono hibridizados sp2 tem cada molécula? 
c. Você pode assinalar quaisquer semelhanças em sua estrutura? 
 
 
 
 
 
 
 
 
 
8) A carvona, uma substância responsável pelo odor da hortelã, tem a estrutura a seguir. 
Diga quantos hidrogênios estão ligados a cada carbono e dê a fórmula molecular da 
carvona. 
 
 
 
 
 
9) Represente as fórmulas de Lewis para os compostos a seguir. 
 
 
 
10) Indique a carga formal no átomo de O e N nas seguintes moléculas. 
 
 
 
 
 
 
 
 
11) Por que a ligação H-H (0,74 Å) é mais curta do que uma ligação C-C (1,54 Å)? 
 
12) Quais das substâncias a seguir formarão ligações de hidrogênio entre suas moléculas? 
 
 
 
 
 
 
 
13) Liste as substâncias a seguir em ordem decrescente de ponto de ebulição. 
 
 
 
 
14) a) Qual das ligações indicadas de cada molécula é a menor? 
b) Indique a hibridização dos átomos de C, O e N em cada uma das moléculas.24 CHAPTER 1 Structure and Bonding
Thomsonl'lO Click Organic
Interactive to learn how to
interconvert skeletal structures,
condensed structures, and
molecular models.
One further comment: although such groupings as -CH3, -OH, and -NH2
are usually written with the C, 0, or N atom first and the H atom second, the order
of writing is sometimes inverted to H3C-, HO-, and H2N- if needed to make the
bonding connections in a molecule clearer. Larger units such as -CH2CH3 are not
inverted, though; we don't write H3CH2C- because it would be confusing.There are,
however, no well-defined rules that cover all cases; it's largely a matter of preference.
Inverted order to
show C-C bond/ /
Inverted order to
show 0-( bond
Not inve rted/ /
CH,CH'DCH,CH,
H2
N
"" NHz
Inverted order to
show N-C bond
WORKED 1.3 Interpreting Line-Bond Structures
Carvone, a substance respo nsible for the odor of spearmint, has the following struc-
ture. Tell how many hydrogens are bonded to each carbon, and give the molecular
formula of carvone.
Carvone
Strategy The end of a line represents a carbon atom with 3 hydrogens, CH3; a two-way inter-
sect ion is a carbon atom with Zhydrogens, CH2; a three-way intersection is a carbon
atom with 1 hydrogen, CH; and a four-way intersection is a carbon atom with no
attached hydrogens.
Solution
HO
21-1
Problem 1.15 ! Tell how many hydrogens are bonded to each carbon ill the following compounds,Iand give the molecular formula of each substance:
I {a) OH lbl 0
i
I
Adrenaline Estrone (a hormone!
34 CHAPTER 1 Structure and Bonding
1.53 There are h\1O different substances with the formula C3H6. Drawboth, and tell
how they differ.
1.54 There are two different substances with the formula CzH60. Draw both, and
tell how they differ.
1.55 There are three different substances that contain a carbon-carbon double bond
and have the formula C4Hs. Draw them. and tell how they differ.
1.56 Among the most common over-the-counter drugs you might find in a medi-
cine cabinet are mild pain relievers such ibuprofen (Advil, Motrin). naproxen
(Aleve), and acetaminophen (Tylenol).
Ibuprofen
aIIc
'OH
Naproxen
aIIc
'OH
Han oI II// CN/ 'CHI 3
H
Acetaminophen
(a) How many sp3-hybridized carbons does each molecule have?
(b) How many sp2-hybridized carbons does each molecule have?
(c) Can you spot any similarities in their structures?
• Assignable in OWL
58 C H A P T E R 1 Electronic Structure and Bonding • Acids and Bases
59. a. Which of the indicated bonds in each molecule is shorter?
b. Indicate the hybridization of the C, O, and N atoms in each of the molecules.
1. 3. 5.
2. 4.
60. For each of the following compounds, draw the form in which it will predominate at and 
a. b. c.
61. Which of the following molecules have tetrahedral bond angles?
62. Do the hybridized carbons and the indicated atoms lie in the same plane?
63. Give the products of the following acid–base reactions, and indicate whether reactants or products are favored at equilibrium (use
the values that are given in Section 1.17):
a. c.
b. d.
64. For each of the following molecules, indicate the hybridization of each carbon atom and give the approximate values of all the
bond angles:
a. b. c.
65. a. Estimate the value of each of the following acids without using a calculator (i.e., between 3 and 4, between 9 and 10, etc.):
1. nitrous acid 4. hydrogen cyanide (HCN),
2. nitric acid 5. formic acid (HCOOH),
3. bicarbonate 
b. Determine the values, using a calculator.
c. Which is the strongest acid?
66. a. List the following carboxylic acids in order of decreasing acidity:
1. 2. 3. 4.
b. How does the presence of an electronegative substituent such as Cl affect the acidity of a carboxylic acid?
c. How does the location of the substituent affect the acidity of a carboxylic acid?
67. Draw a Lewis structure for each of the following species:
68. a. For each of the following pairs of reactions, indicate which one has the more favorable equilibrium constant (that is, which one
most favors products):
a. CH3N2+ b. CH2N2 c. N3– d. N2O (arranged NNO)
CH3CHCH2COOH
Ka = 8.9 × 10
−5
Cl
ClCH2CH2CH2COOH
Ka = 2.96 × 10
−5
CH3CH2CHCOOH
Ka = 1.39 × 10
−3
Cl
CH3CH2CH2COOH
Ka = 1.52 × 10
−5
pKa
(HCO3 -), Ka = 6.3 * 10-11
Ka = 2.0 * 10-4(HNO3), Ka = 22
Ka = 7.9 * 10-10(HNO2), Ka = 4.0 * 10-4
pKa
CH3CH2CH3CH3CH“CH2CH3C‚CH
+CH3CH2OH HCl+CH3CH2OH −NH2
O
+CH3COH CH3NH2
O
+CH3COH CH3O−
pKa
CH3
CH3
CH3
H
H
CH2CH3
C C
CH3
H
H
CH3
C C
sp2
H2O H3O+ +CH3 BF3 NH3 +NH4 –CH3 
pKa ! 12.4pKa ! 11.0pKa ! 4.8
CF3CH2OHCH3CH2N
+
H3CH3COOH
pH = 14:pH = 3, pH = 6, pH = 10,
CHC C H
H
H
C
O
OHCH3CCH2
CHC CC C
CH3
CH3
H
H
H
CH2CH2N CHCH3CH3NHCHC CHCH3CH
BRUI01-001_059r4 20-03-2003 2:59 PM Page 58
PROBLEM 20!
a. Which of the following compounds will form hydrogen bonds between its molecules?
1. 4.
2. 5.
3. 6.
b. Which of the preceding compounds form hydrogen bonds with a solvent such as
ethanol?
PROBLEM 21
Explain why
a. has a higher boiling point than 
b. has a higher boiling point than 
c. has a higher boiling point than HF (20 °C).
PROBLEM 22!
List the following compounds in order of decreasing boiling point:
Both van der Waals forces and dipole–dipole interactions must be overcome in
order for an alkyl halide to boil. As the halogen atom increases in size, the size of its
electron cloud increases. As a result, both the van der Waals contact area and the
polarizability of the electron cloud increase.
Polarizability indicates how readily an electron cloud can be distorted. The larger
the atom, the more loosely it holds the electrons in its outermost shell, and the more
they can be distorted. The more polarizable the atom, the stronger are the van der Waals
interactions. Therefore, an alkyl fluoride has a lower boiling point than an alkyl chlo-
ride with the same alkyl group. Similarly, alkyl chlorides have lower boiling points than
alkyl bromides, which have lower boiling points than alkyl iodides (Table 2.6).
PROBLEM 23
List the following compounds in order of decreasing boiling point:
a.
b.
c.
CH3CH2CH2CH2CH2OH
CH3CH2CH2CH2CH3 CH3CH2CH2CH2OH CH3CH2CH2CH2Cl
CH3CH2CH2CH2CH2CH2CH2CH3 CH3CH2CH2CH2CH2CH2CH2CH2CH3
CH3CHCH2CH2CH2CH2CH3
CH3 CH3
CH3C
CH3
CH3
CCH3
CH3
CH3CH2CH2CH2CH2CH2Br CH3CH2CH2CH2Br CH3CH2CH2CH2CH2Br
OH OH
HO OH
OH
OH
NH2
H2O
NH3 (-33 °C).H2O
CH3OH (65 °C).H2O
CH3CH2CH2CH2FCH3CH2CH2CH2Br
CH3CH2OCH2CH2OHCH3CH2N(CH3)2
CH3CH2CH2NHCH3CH3CH2CH2COOH
Section 2.9 Physical Properties of Alkanes, Alkyl Halides, Alcohols, Ethers, and Amines 85
Table 2.6 Comparative Boiling Points of Alkanes and Alkyl Halides (°C)
Y
H F Cl Br I
3.6 42.4
12.3 38.4 72.3
46.6 71.0 102.5
32.5 78.4 101.6 130.5
36.1 62.8 107.8 129.6 157.0CH3CH2CH2CH2CH2¬Y
-0.5CH3CH2CH2CH2¬Y
-2.5-42.1CH3CH2CH2¬Y
-37.7-88.6CH3CH2¬Y
-24.2-78.4-161.7CH3¬Y
BRUI02-060_108r4 20-03-2003 11:47 AM Page 85
PROBLEM 20!
a. Which of the following compounds will form hydrogen bonds between its molecules?
1. 4.
2. 5.
3. 6.
b. Which of the preceding compounds form hydrogen bonds with a solvent such as
ethanol?
PROBLEM 21
Explain why
a. has a higher boiling point than 
b. has a higher boiling point than 
c. has a higher boiling point than HF (20 °C).
PROBLEM 22!
List the following compounds in order of decreasing boiling point:
Both van der Waals forces and dipole–dipole interactions must be overcome in
order for an alkyl halide to boil. As the halogen atom increases in size, the size of its
electron cloud increases. As a result, both the van der Waals contact area and the
polarizability of the electron cloud increase.
Polarizability indicateshow readily an electron cloud can be distorted. The larger
the atom, the more loosely it holds the electrons in its outermost shell, and the more
they can be distorted. The more polarizable the atom, the stronger are the van der Waals
interactions. Therefore, an alkyl fluoride has a lower boiling point than an alkyl chlo-
ride with the same alkyl group. Similarly, alkyl chlorides have lower boiling points than
alkyl bromides, which have lower boiling points than alkyl iodides (Table 2.6).
PROBLEM 23
List the following compounds in order of decreasing boiling point:
a.
b.
c.
CH3CH2CH2CH2CH2OH
CH3CH2CH2CH2CH3 CH3CH2CH2CH2OH CH3CH2CH2CH2Cl
CH3CH2CH2CH2CH2CH2CH2CH3 CH3CH2CH2CH2CH2CH2CH2CH2CH3
CH3CHCH2CH2CH2CH2CH3
CH3 CH3
CH3C
CH3
CH3
CCH3
CH3
CH3CH2CH2CH2CH2CH2Br CH3CH2CH2CH2Br CH3CH2CH2CH2CH2Br
OH OH
HO OH
OH
OH
NH2
H2O
NH3 (-33 °C).H2O
CH3OH (65 °C).H2O
CH3CH2CH2CH2FCH3CH2CH2CH2Br
CH3CH2OCH2CH2OHCH3CH2N(CH3)2
CH3CH2CH2NHCH3CH3CH2CH2COOH
Section 2.9 Physical Properties of Alkanes, Alkyl Halides, Alcohols, Ethers, and Amines 85
Table 2.6 Comparative Boiling Points of Alkanes and Alkyl Halides (°C)
Y
H F Cl Br I
3.6 42.4
12.3 38.4 72.3
46.6 71.0 102.5
32.5 78.4 101.6 130.5
36.1 62.8 107.8 129.6 157.0CH3CH2CH2CH2CH2¬Y
-0.5CH3CH2CH2CH2¬Y
-2.5-42.1CH3CH2CH2¬Y
-37.7-88.6CH3CH2¬Y
-24.2-78.4-161.7CH3¬Y
BRUI02-060_108r4 20-03-2003 11:47 AM Page 85
15) Qual das estruturas abaixo não pode ser estrutura de ressonância para o nitrometano? 
 
a) b) 
c) d) 
 
 
H C
H
H
N
+
O
O
-
H C
H
H
N
O
-
O
-
2
+
H C
H
H
N
+
O
O
-
H C
H
N
+
O
-
O H