Name:
Problem Set Chapter 4: Intro to Alkenes: Structure and Reactivity
4.4 Name each of the following compounds, including the proper designation of the double-bond
stereochemistry:
H
H
(a)
H2C=CHCH2
C
CH3
C
(CH ) CHCH
3 2
2
(b)
C
= H
CH3
H3C
H
H
H3C
4.6 In each case, which group receives the higher priority?
(a)
(b)
CH3CH2
(c)
CH
CH3 O
Cl 2HC
(CH3)3C
H2C
(CH3)3C
C
C
C
CH
(d)
H3C
CH
CH
C
HC
C
OCH3
HO
4.7 Calculate the unsaturation number for each of the following compounds:
(a) C3H4Cl4
(b) C5H8N2
4.9 A compound has the molecular formula C20H34O2. Certain structural evidence suggests that the compound
contains two methyl groups and no carbon-carbon double bonds. Give one structure consistent with these
findings in which all rings are six-membered. (Many structures are possible.)
4.10 Which of the following cannot be correct formula(s) for an organic compound? Explain.
(a) C10H20N3
StudyProbCh4 (b) C10H20N2O2
(c) C10H27N3O2
(d) C10H16O2
1 4.11. Which compound in each case should have the larger dipole moment? Explain.
(a) cis-2-butene or trans-2-butene
(b) propene or 2-methylpropene
4.14 (a) If the standard enthalpy change for the reaction 2-ethyl-1-butene → 1-hexene is +15.3 kJ/mol, and if
ΔH of for 1-hexene is -40.5 kJ/mol, what is ΔH of for 2-ethyl-1-butene?
(b) Which isomer in part (a) is more stable?
4.16. Within each series arrange the compounds in order of increasing stability:
CH3
(a)
H3C
A B H3C
C(CH3)3
C
(b)
H3C
C
H
H
C
H
H
C
CH2CH(CH3)2
A B 4.21 In each case, give two different alkene starting materials that would react with H-Br to give the compound
shown as the major (or only) addition product.
(a)
CH3 CH3
H3C
C
CH CH3
Br
StudyProbCh4 2 4.22 Which of the following carbocations is likely to rearrange? If rearrangement occurs, give the structure of
the rearranged carbocation.
(a)
(b)
(c) CH3
H
CH3 CH3
CH3
H3C CH CH2 C CH3
H3C CH C CH3
+
CH3
+
+
4.24 Only one of the following three alkyl halides can be prepared as the major product of the addition of HBr
to an alkene. Which compound can be prepared in this way? Explain why the other two cannot be
prepared in this way.
Br CH3
Br
CH3 CH2 CH2 CH2CH2Br
A
H3C
CH CH2 CH2 CH3
B
CH3 CH C
C
C2 H 5
CH3
4.31 Apply Hammond’s postulate to decide which reaction is faster: addition of HBr to 2-methylpropene or
addition of HBr to trans-2-butene. Assume that the energy difference between the starting alkenes can be
ignored. Why is this assumption necessary?
StudyProbCh4 3 4.35 The alkene 3,3-dimethyl-1-butene undergoes acid-catalyzed hydration with rearrangement. Use the
mechanism of hydration and rearrangement to predict the structure of the hydration product of this alkene.
4.36 (a) The product in Eq. 4-43 does not come to equilibrium with the starting alkene. However, it does come
to equilibrium with two other alkenes. What are their structures?
(b) Why isn’t the alkene starting material in Eq. 4.43 part of the equilibrium mixture?
H
H3C
C
OH
H3O+
CH CH2
+ H2O
H3C
C
CH2 CH3
(4.43)
CH3
CH3
4.51 An alkene X with molecular formula C7H12 adds HBr to give a single alkyl halide Y with molecular
formula C7H13Br and undergoes catalytic hydrogenation to give 1,1-dimethylcyclopentane. Draw the
structures of X and Y.
4.52 Give the structures of the two stereoisomeric alkenes with the molecular formula C6H12 that react with HI
to give the same single product and undergo catalytic hydrogenation to give hexane.
StudyProbCh4 4 4.55 A reaction ABCD has the reaction free-energy diagram shown
in Fig. P4.55.
(a) Which compound is present in greatest amount when the reaction
comes to equilibrium? In least amount?
(b) What is the rate-limiting step of the reaction?
(c) Using a vertical arrow, label the standard free energy of activation
for the overall AD reaction.
(d) Which reaction of compound C is faster: C B or CD? How do
you know?
4.63 The curved-arrow notation can be used to understand seemingly new reactions as simple extensions of
what you already know. This is the first step in developing an ability to use the notation to predict new
reactions. Provide a curved-arrow mechanism for the following reaction. H3C
C
CH CH2 CH2 OH
dilute aqueous
H3C
H2SO4
H3C
H3C
O
4.66 Using the curved-arrow notation, suggest a mechanism for the reaction shown in Fig. P4.66. Use
Hammond’s postulate to decide which double bond should protonate first.
H3C
••
C
CH CH2 CH2 CH CH2 + H2O ••
H2SO4
••
H3C
StudyProbCh4 H3C
H3C
•OH
•
5