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Chemistry

Catherine E. Housecroft, Edwin C. Constable

Chapter 26

Alkenes and alkynes - all with Video Answers

Educators

Chapter Questions

01:39

Problem 1

Give systematic names to the following compounds:
a.(FIGURE CAN'T COPY)
b.(FIGURE CAN'T COPY)
c.(FIGURE CAN'T COPY)
d.(FIGURE CAN'T COPY)
e.(FIGURE CAN'T COPY)
f.(FIGURE CAN'T COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
03:08

Problem 2

The IR spectrum of octa-I,7-diyne is shown in Figure $26.10 .$ Assign the adsorptions above $1800 \mathrm{cm}^{-1}$.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
03:06

Problem 3

How many signals would you expect to see in the proton decoupled $^{13}$ C NMR spectra of
(a) penta-l,4-dicne and (b) penta-2,4-dicne? Could you distinguish the $(E)$ - and $(Z)$ -isomers of penta-2,4-diene using ' C NMR spectroscopy?

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
06:41

Problem 4

(a) Two isomers of cyclooctadicne exhibit two and four signals respectively in their $^{13}$ C NMR spectra. Draw the structures of the isomers and assign one of the spectra to cach. (b) A third isomer of $\mathrm{C}_{8} \mathrm{H}_{12}$ has a bicyclic structure and its $^{13} \mathrm{C}$ NMR spectrum contains three signals. Suggest a structure for this isomer. Rationalize why the "H NMR spectrum of this compound has four signals.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
07:07

Problem 5

Draw the structure of hexa-l, 5 -diyne and interpret the following spectroscopic data. (a) The IR spectrum contains strong to medium absorptions at 3665,2922,2851 and $2123 \mathrm{cm}^{-1}$ in addition to bands in the fingerprint region. (b) The $^{13}$ C NMR spectrum has signals at $\delta 82.4,69.5$ and $18.6 \mathrm{ppm} .$ (c) The $^{1}$ H NMR spectrum has singlets at $\delta 2.06$ and 2.43 ppm.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
05:16

Problem 6

Develop a bonding scheme (similar to those in Figure 26.1 ) for allenc, $\mathrm{H}_{2} \mathrm{C}=\mathrm{C}=\mathrm{CH}_{2}$.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
02:32

Problem 7

Draw structural formulae for the following compounds: (a) cyclohcpta-1,3-diene;
(b) 2 -methylpentene, (c) 4 -methylhexene,
(d) 1,2 -dibromocyclopentenc and
(e) cyclododeca- 1,5,9 -tricne.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
06:38

Problem 8

Why is a $[2+2]$ cycloaddition driven photolytically, while a $[4+2]$ cycloaddition is thermally promoted?

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
02:08

Problem 9

Suggest what products are formed in the reactions of buta-I,3-dicne with:
a.(FIGURE CAN'T COPY)
b.(FIGURE CAN'T COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
03:50

Problem 10

Suggest products for the following reactions:
a.(FIGURE CAN'T COPY)
b.(FIGURE CAN'T COPY)
c.(FIGURE CAN'T COPY)
d.(FIGURE CAN'T COPY)
e.(FIGURE CAN'T COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
02:09

Problem 11

Values of the bond enthalpy terms for $\mathrm{C}=\mathrm{C}, \mathrm{C}-\mathrm{C}$ $\mathrm{H}-\mathrm{H}$ and $\mathrm{C}-\mathrm{H}$ bonds are 598,346,436 and $416 \mathrm{kJ} \mathrm{mol}^{-1} .$ Determine the cnthalpy change associated with the hydrogenation of $\mathrm{C}_{2} \mathrm{H}_{4}$. Compare your answer with that determined using values of $\Delta_{f} H^{\circ}$ for $C_{2} H_{4}(g)$ and $C_{2} H_{6}(g)$ of +52.5 and $-83.8 \mathrm{kJ} \mathrm{mol}^{-1}$.

Mahipal Kumawat
Mahipal Kumawat
Numerade Educator
09:57

Problem 12

(a) Suggest a mechanism for the reaction of HBr with 2 -methylbut-l-cne under polar conditions and indicate the relative product distribution that you might expect. (b) How does the reaction differ if it is carricd out in the presence of a radical initiator?

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
04:03

Problem 13

What happens when $\mathrm{Br}_{2}$ reacts with cyclohexene in the absence of a radical initiator? Include in your answer discussion of the mechanism, evidence for proposed intermediates, and an explanation of the stereochemistry of the product.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
02:17

Problem 14

Consider the addition of HCl to (Z)-but-2-ene. Discuss how the stereochemistry of the product is affected by whether HCl adds in a syn- or anti-manner.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
08:51

Problem 15

Oxidations of alkenes include reactions with $\mathbf{O}_{3}$ and OsO, Using hex-3-cne as the example, discuss the use of these reagents to produce diols and aldchydes, paying attention to the stercochemistry of the products where appropriate.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
07:52

Problem 16

(a) Rewrite equations $26.47-26.49$ showing appropriate curly arrows. (b) Suggest the product of the reaction of hex-l-ene with NBS.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
04:01

Problem 17

How would you carry out the following transformations?
a.(FIGURE CAN'T COPY)
b.(FIGURE CAN'T COPY)
c.(FIGURE CAN'T COPY)
d.(FIGURE CAN'T COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
11:24

Problem 18

The commercial polymerization of propene requires the formation of a stereoregular polymer (sce Box 26.3 ). Suggest a mechanism for the radical polymerization of propene that is consistent with the formation of a stereoregular polymer with methyl side chains.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
10:23

Problem 19

Using the isomerization of hex-l-cne to hex-2-ene as an example, explain how (a) an acid and (b) a base catalyse the migration of a $\mathrm{C}=$ C double bond.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
07:16

Problem 20

9-Borabicyclo[3.3.1)nonane (commonly called 9-BBN) is a selective hydroborating agent and has the following structure: (FIGURE CAN'T COPY) Starting from a suitable cyclic diene, suggest a method of preparing 9-BBN. What other isomers might be formed in the reaction?

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
12:10

Problem 21

Comment on the complications that may be encountered when an alkyne such as hept-3-yne reacts with $\mathrm{H}_{2}$. What methods are available to overcome the problems you describe?

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
08:41

Problem 22

Using diagram 26.16 to help you, draw a schematic representation of the hyperconjugation that stabilizes the carbenium ion formed in the first step in scheme $26.78 .$ Comment on the stereochemistry of the carbenium ion.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
06:33

Problem 23

Which of the following species can undergo keto-enol tautomerism? Give the keto-form where appropriate.
a.(FIGURE CAN'T COPY)
b.(FIGURE CAN'T COPY)
c.(FIGURE CAN'T COPY)
d.(FIGURE CAN'T COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
02:09

Problem 24

Suggest products for the following reactions:
a.(FIGURE CAN'T COPY)
b.(FIGURE CAN'T COPY)
c.(FIGURE CAN'T COPY)
d.(FIGURE CAN'T COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
03:48

Problem 25

Suggest suitable reagents to carry out the multi-step syntheses shown below. (FIGURE CAN'T COPY)

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
03:40

Problem 26

(a) The bromination of $(Z)$ -pent-2-ene produces a mixture of $(2 R, 3 R)-2,3$ -dibromopentane and $(2 S, 3 S)-2,3$ -dibromopentane. Rationalize this observation. (b) What is the stereochemistry of the product of the reaction of pentene and $\mathrm{Br}_{2} ?$

Nicholas Sacco
Nicholas Sacco
Numerade Educator
10:57

Problem 27

Two acyclic isomers of $\mathrm{C}_{6} \mathrm{H}_{10} .$ A and $\mathrm{B}$ show the following signals in their $^{1} \mathrm{H}$ NMR spectra: $\mathbf{A} \quad \delta / \mathrm{ppm} 1.13 \text { (doublet, } 6 \mathrm{H}), 1.78(\text { singlet, } 3 \mathrm{H})$ $$2.50 \text { (scptet, } 1 \mathrm{H})$$ $\mathbf{B} \quad \delta / \mathrm{ppm} 0.99 \text { (doublet, } 6 \mathrm{H}), 1.86$ (multiplet, 1H), 1.96 (singlet, $1 \mathrm{H}$ ), 2.08 (doublet, $2 \mathrm{H}$ ) Compound $\mathbf{B}$ reacts with $\mathrm{KNH}_{2},$ but A does not undergo an analogous reaction. Both $A$ and $B$ add $\mathrm{Br}_{2}$ to give compounds $\mathrm{C}$ and $\mathrm{D}$ which analyse as having $17.9 \%$ C and $2.5 \%$ H. Suggest possible structures for $\mathbf{A}, \mathbf{B}, \mathbf{C}$ and $\mathbf{D}$.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
06:14

Problem 28

The following alkenes are pheromone sex attractants in several families of moths. Draw the structure of each compound, showing clearly the stereochemistry. Why do not all the $\mathrm{C}=\mathrm{C}$ bonds require stereochemical descriptors? (a) (11Z)Pentadeca-1,11-dicne, (b) (3Z,6Z,9Z)-nonadeca3,6,9 -tricne, $(c)(3 Z, 6 Z)$ -icosa- $3,6-$ dicne, $(d)(S)-14$ methyloctadec-l-ene, (c) $(3 E, 6 Z, 9 Z)$ -nonadeca1,3,6,9 -tetracne.

Kevin Barayuga
Kevin Barayuga
Numerade Educator
11:43

Problem 29

The polymerization of alkenes leads to many materials that are in daily use. Three examples of polymers are shown below:
a.(FIGURE CAN'T COPY)
b.(FIGURE CAN'T COPY)
c.(FIGURE CAN'T COPY)
(a) What is the monomer used in the production of each polymer? (b) By what name or abbreviation is each polymer known? (c) Give one application of each polymer. (d) Assuming a radical mechanism, outline how polymer $A$ is formed from its monomer.

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
07:43

Problem 30

The structures of polyvinyl alcohol (PVA) and polyvinyl acetate (PVAc) are shown below: (FIGURE CAN'T COPY) Whereas PVA is used in some contact lens solutions, PVAc is commonly encountered as 'PVA white glue' which is used, for example, as an adhesive for wood products. Hydrolysis of PVAc with NaOH leads to the replacement of some or all of the acctate groups by OH groups. Figure 26.11 shows the IR spectrum of the monomer used to make PVA white glue. (a) Draw the structures of the monomers used for the formation of PVA and PVAc. (b) Assign the absorptions in Figure 26.11 that come at 3100,1762 and $1649 \mathrm{cm}^{-1} .$ What general term is used to describe the region of the spectrum below $1500 \mathrm{cm}^{-1} ?$ (c) What will be the most significant change in the IR spectrum in Figure 26.11 on going from monomer to polymer? (d) What changes in the IR spectrum would you monitor to see whether all the acetate groups are replaced by OH groups during the hydrolysis?

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator