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CHAPTER 10 HW: ALKENES
CIS-TRANS AND EZ ISOMERISM
1. Classify each structure as either cis, trans, E, or Z. Then beside each, draw the related stereoisomer (e.g. if the E isomer is shown, draw the Z isomer).
Structure and
Stereoisomer
cis, trans, E, or Z ?
Structure and
Stereoisomer
cis, trans, E, or Z ?
Structure and
Stereoisomer
cis, trans, E, or Z ?
2. Draw the following:
a. Z-2-bromo-4-methyl-2-pentene b. Two stereoisomers of C5H10 c. Two structural isomers of C5H10
BrBr
CH3
Cl
HO
OH
O H
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3. Give the IUPAC name for each compound, including cis/trans, R/S, or E/Z stereochemistry where necessary.
Structure
Name
Structure
Name
Structure
Name
ALKENE REACTION WITH HX
4. Give the curved arrow mechanism for the following reactions. In your mechanisms, include all lone pairs and formal charge.
CH3
OHOH
ClCl
a. H3CC
C
H
H
H
HClH3C
CC
H
H
H Cl
H
b. HBrBr
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5. For the following reaction,
a. Draw the curved arrow mechanism that shows formation of both products.
b. Draw the energy diagram for each reaction (both pathways superimposed on one diagram, or side-by-side to relative scale).
c. Identify the major product and explain why it is favored over the other product.
6. Explain which is expected to be the major product in this reaction. Use an energy diagram with your explanation.
HII
I+
HClCl
+
Cl
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7. In this reaction, both DH˚ and DS˚ are negative. Explain.
8. Give the curved arrow mechanism for these reactions.
9. Explain why the major product in this reaction is Q, not R.
HCl Cl
a. HClCl
b. HII
HBrBr
Br+
Q R
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10. Explain why two products are formed in this reaction.
HYDRATION
11. For the following reaction,
a. Give the curved arrow mechanism for the reaction, showing formation of both products.
b. Explain which is the major product, and use a complete energy diagram with your explanation.
HI
ICH3 CH3I+
OH
OH +H2SO4H2O
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12. Using the mechanism from the previous problem, explain if acid is catalytic or not in the hydration reaction. [Note: “acid” considers all strong acid forms such as H2SO4 and H3O+.]
13. Give the curved arrow mechanism for each reaction.
a.H2SO4H2O OH
b. OHH2SO4H2O O
c.H2SO4H2O
OH
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SUMMARY OF ALKENE REACTIONS
14. Give the major organic product for the following reactions. If a racemic mixture is expected, draw both products. If a rearrangement is probable, give the product from the rearrangement.
HALOGENATION
15. Give the curved arrow mechanism for each reaction. Include all lone pairs and formal charge.
a. b.HBr HCl
c. d.excess
HI
H2SO4H2O
e.H2SO4H2O
a. Br2Br
Br (racemic)
b.Cl2
Cl
Cl
(racemic)
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16. Explain why the “anti” addition product is formed in this reaction and not the “syn” product.
17. Explain why a rearrangement occurs is reaction (1), but not reaction (2).
18. Molecules X and Y both have a formula of C5H10. Propose a structure of X and Y that is consistent with the observations noted upon addition with a solution of Br2.
Br2
Br
Br
Br
Brnot
anti syn
Br2
HBr
Br
Br
Br(1)
(2)
X Y
2 drops
Br2 in CCl4
2 drops
Br2 in CCl4
Colorless solution
Orange solution
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HALOHYDRIN FORMATION
19. Give the curved arrow mechanism for each reaction.
20. Explain the following: a. The nucleophile mostly attacks the bromonium ion at position X, not position Y.
b. Two products are formed in equal amounts in this reaction.
a.Cl2H2O
Cl
OH
racemic
b.Br2
CH3OHBr
OCH3
racemic
Br
CH3X
Y
Br2
H2OBr Br+
OH OH
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21. Which is the expected major product from this reaction? (All are racemic.)
22. Give the major organic product of each reaction. Indicate if a racemic mixture is expected.
SUMMARY OF ALKENE REACTIONS
23. Fill in the boxes with the correct reagent(s) for each reaction.
Cl2Cl Cl
CH3OH CH3 OCH3OCH3 CH3
C D
Cl Cl
CH3 ClCl CH3
A B
a. Br2 b.Br2H2O
c.Br2
CH3OHd.
a. Br2, H2O
b. NaH
e.Cl2
OH
f.a. Cl2, H2O
b. NaH
a. b.Br
Cl
Cl
(rac.)
c. d.Br
OH
Cl
CH3O
(rac.)(rac.)
e. f.OH
BrCH3Br
(rac.)
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HYDROBORATION-OXIDATION
24. Explain the following features of the hydroboration reaction below.
a. Three moles of alkene react with each mole of BH3.
b. The reaction is “regioselective.” (Explain why it is regioselective.)
c. The reaction is “stereoselective.” (Explain why it is stereoselective.)
25. Give the major organic product for each reaction, paying attention to stereochemistry (syn/anti). Indicate if a racemic mixture is expected.
26. Fill in the boxes with the correct reagents for each reaction.
a. BH3
OH
CH3
3 b. 3 H2O2, 3 OH- 3(rac.)
a. b.a. BH3
b. H2O2, OH-
a. BH3
b. H2O2, OH-
c. d.a. BH3
b. H2O2, OH-
a. BH3
b. H2O2, OH-
OHa. b.
OH
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SUMMARY OF ALKENE REACTIONS
27. Give the major organic product(s) of each reaction. Pay attention to stereochemistry and indicate if a racemic mixture is formed. If a rearrangement is probable, give the product from the rearrangement.
SYNTHESIS
28. Devise a synthesis that can transform each starting material into the product shown. Show all synthetic intermediates and reagents. More than one step is needed in each synthesis.
a. Br2OCH3
b. HCl
c.a. BH3
b. H2O2, OH-d.
H2SO4
O H2O
e.Cl2
OH
a.Br Br
Br (rac.)
b.Cl Br
OH
(rac.)
c.OH
OCH3
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TREE DIAGRAMS FOR 1H NMR SPECTRA
29. Draw a tree diagram to show the expected splitting for the indicated hydrogen atom in each molecule. Then describe the splitting pattern (e.g. doublet of doublets).
Jab= 2 Hz; Jbc= 7 Hz
Jab= 16 Hz; Jbc= 8 Hz
ALKENE NMR
30. How many signals should ideally be present in the 1H NMR spectrum of each compound (how many different hydrogen environments are present)? Use labels (a,b,c...) to show which hydrogen atoms should be grouped together.
31. Assign the 1H NMR spectrum to hydrogen atoms in the structure. Pay attention to splitting + relative
J’s.
Cl
Hb
Cl
Cl HaOH
Hc Hc
Ha
CH3
Hb
cH3C
O
N
Ha. O
CH3b. N
Hc.
NH2
01234567PPM
1H, dd 1H, dd 1H, dd 2H, sa b c d
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32. Determine a structure that matches the molecular formula and 1H NMR spectrum for each problem. Then assign all peaks in the 1H NMR spectrum to hydrogen atoms in the structure.
0123456789PPM
1H 1H
3H, s
2H, d3H, m
C10H10O
01234567PPM
6H, d
3H, d
1H, m1H, d1H, mJ = 10.2 Hz
C7H12O2Note: J < 2 Hz are not included in the splitting
0246810PPM
1H, s
1H, dd 1H, dd 1H, dd
2H, q
3H, tC4H9N