Exam 4 Study Guide
Alkynes (Chp 7) and Nucleophilic Substitution and -Elimination (Chp 9)
The following topics will be covered on the exam. Know them.
Chapter 7
 Nomenclature of alkynes; draw structure of an alkyne when given IUPAC name, or vice
versa.
 Know the following reactions (know the reaction steps, not electron movement:
Preparation of alkynes:
Alkylation with alkyne anions with methyl and primary haloalkanes
From alkenes—dehydrohalogenation
Hydration of alkynes to aldehydes and ketones
Hydroboration/oxidation
Acid-catalyzed hydration
Reduction of Alkynes
Catalytic reduction (metals, Lindlar’s catalyst)
Hydroboration-protonolysis
Dissolving-metal reduction
 Know the following reactions and stereochemistry:
Electrophilic Addition to Alkynes
Addition of Br2 and Cl2
Addition of HBr and HCl
 Synthesis—be able to provide a multi-step synthesis of a target molecule
Chapter 9
 Nucleophilic substitution in haloalkanes
 SN2 mechanism
o bimolecular reaction
o transition state
o energy diagram
o stereochemistry
 SN1 mechanism
o unimolecular reaction
o transition state/carbocation formation
o energy diagram
o stereochemistry
 Criteria for deciding between an SN1 and an SN2 occurring
o Electronic vs steric
o Carbocation stability and rearrangement (SN1)
o Leaving group stability
o Solvent effects
o Strength of the nucleophile
o Kinetics
o Summarize SN1 vs SN2 rxn for haloalkanes
1


-Elimination
o Zaitsev products
o E1 vs E2 mechanism
 Uni- vs bimolecular
 Intermediate vs transition state
 Energy diagrams
 Kinetics
 Stereochemistry
o Summarize E1 vs E2 rxn for haloalkanes
Be able to determine the results of the competition between substitution and elimination
reactions, writing all resulting products (indicating major and minor)
Practice Problems:
1. Draw structural formulas for the major product(s) formed in the reaction of 3-hexyne
with each of the following reagents
a. xs H2/Pt
b. Na in NH3(l)
c. NaNH2 in NH3(l)
d. BH3 followed by CH3COOH
e. HBr (1 equivalent)
f. H2O in H2SO4/HgSO4
2. Draw the structure for the enol and ketone/aldehyde resulting from the following
reactions.
HgSO
a. CH3(CH2)5C
CH + H2O H SO
4
2
4
(sia)2BH
b. CH3(CH2)5C
CH + H2O
NaOH/H2O2
3. What reagents and experimental conditions would you use to convert propyne into the
products below? (more than one step may be required)
a.
b.
c.
2
d.
4. Show reagents to bring about each conversion:
5. From each pair select the strongest nucleophile
a. H2O or OHb. Cl- or I- in methanol
c. Cl- or I- in DMSO
d. CH3OCH3 or CH3SCH3
6. Draw the structural formula for the product of each SN2 reaction.
a. CH3CH2CH2Cl + CH3CH2O- Na+ ethanol
b. (CH3)3N + CH3I
c.
acetone
+ NH3
ethanol
7. Draw the structural formula for the product of each SN1 reaction.
a.
+ CH3CH2OH
ethanol
S enantiomer
b.
+ CH3OH
methanol
8. Draw structural formulas for the alkene(s) formed by treatment with sodium ethoxide in
ethanol. Assume an E2 mechanism.
a.
b.
3
c.
9. To which mechanism (SN1, SN2, E1, E2) does each statement apply?
a. Involves a carbocation intermediate.
b. Is first order in haloalkane and first order in nucleophile.
c. Involves inversion of configuration at the site of substitution.
d. Involves retention of configuration at the site of substitution.
e. Substitution at a stereocenter gives predominantly a racemic product.
f. Is greatly accelerated in protic solvents with increasing polarity.
g. Order of reactivity of haloalkanes is 3º>2º >1º.
h. Order of reactivity of haloalkanes is methyl>1º>2º >3º.
10. Draw structural formulas for the organic product(s) of the following reactions and specify
the likely mechanism.
a.
b.
+ CH3OH
+
methanol
DMSO
(R)-2-chlorobutane
c.
+ CH3O-Na+ methanol
11. Show how to convert the starting material into the desired product (might be more than
one step).
a.
b.
c.
d.
e.
f.
4