Embed Size (px)
DESCRIPTION
321
Citation preview
1!
Chapter 10. Alkynes
"Junha Jeon!
Department of Chemistry!University of Texas at Arlington!
Arlington, Texas 76019!"!
Chem 2321, Fall ‘13!
Chapter 10. Alkynes
"Junha Jeon!
Department of Chemistry!University of Texas at Arlington!
Arlington, Texas 76019!"!
Chem 2321, Fall ‘13!
10.1 Introduction to Alkyne!
C CH
HEthyne or Acetylene!
Introduction to Alkyne!
C CH
HEthyne or Acetylene!
Nomenclature (IUPAC)!
• Given the presence of two pi bonds and their associated electron density, alkynes are similar to alkenes in their ability to act as either nucleophiles or as bases.!
10.2 Nomenclature of Alkynes!
2!
Alkynes are named using the same procedure we used in Chapter 4 to name alkanes with minor modifications:!
1. Identify the parent chain, which should include the C≡C triple bond.!
2. Identify and name the substituents.!3. Assign a locant (and prefix if necessary) to each substituent, giving
the C≡C triple bond the lowest number possible.!4. List the numbered substituents before the parent name in
alphabetical order. Ignore prefixes (except iso and neo) when ordering alphabetically.!
5. The C≡C triple bond locant is placed either just before the parent name or just before the -yne suffix.!
Nomenclature of Alkynes!
Alkynes are named using the same procedure we used in Chapter 4 to name alkanes with minor modifications:!
1. Identify the parent chain, which should include the C≡C triple bond.!
2. Identify and name the substituents.!3. Assign a locant (and prefix if necessary) to each substituent, giving
the C≡C triple bond the lowest number possible.!4. List the numbered substituents before the parent name in
alphabetical order. Ignore prefixes (except iso and neo) when ordering alphabetically.!
5. The C≡C triple bond locant is placed either just before the parent name or just before the -yne suffix.!
Nomenclature of Alkynes!
Alkynes are named using the same procedure we used in Chapter 4 to name alkanes with minor modifications:!
1. Identify the parent chain, which should include the C≡C triple bond.!
2. Identify and name the substituents.!3. Assign a locant (and prefix if necessary) to each substituent, giving
the C≡C triple bond the lowest number possible.!4. List the numbered substituents before the parent name in
alphabetical order. Ignore prefixes (except iso and neo) when ordering alphabetically.!
5. The C≡C triple bond locant is placed either just before the parent name or just before the -yne suffix.!
Nomenclature of Alkynes!
Alkynes are named using the same procedure we used in Chapter 4 to name alkanes with minor modifications:!
1. Identify the parent chain, which should include the C≡C triple bond.!
2. Identify and name the substituents.!3. Assign a locant (and prefix if necessary) to each substituent, giving
the C≡C triple bond the lowest number possible.!4. List the numbered substituents before the parent name in
alphabetical order. Ignore prefixes (except iso and neo) when ordering alphabetically.!
5. The C≡C triple bond locant is placed either just before the parent name or just before the -yne suffix.!
Nomenclature of Alkynes!
Nomenclature of Alkynes!
1. Identify the parent chain, which should include the C≡C triple bond.!2. Identify and name the substituents.!3. Assign a locant (and prefix if necessary) to each substituent, giving
the C≡C triple bond the lowest number possible.!4. List the numbered substituents before the parent name in
alphabetical order. Ignore prefixes (except iso) when ordering alphabetically.!
5. The C≡C triple bond locant is placed either just before the parent name or just before the -yne suffix.!
Nomenclature of Alkynes!
1. Identify the parent chain, which should include the C≡C triple bond.!2. Identify and name the substituents.!3. Assign a locant (and prefix if necessary) to each substituent, giving
the C≡C triple bond the lowest number possible.!4. List the numbered substituents before the parent name in
alphabetical order. Ignore prefixes (except iso) when ordering alphabetically.!
5. The C≡C triple bond locant is placed either just before the parent name or just before the -yne suffix.!
3!
Nomenclature of Alkynes!
1. Identify the parent chain, which should include the C≡C triple bond.!2. Identify and name the substituents.!3. Assign a locant (and prefix if necessary) to each substituent, giving
the C≡C triple bond the lowest number possible.!4. List the numbered substituents before the parent name in
alphabetical order. Ignore prefixes (except iso) when ordering alphabetically.!
5. The C≡C triple bond locant is placed either just before the parent name or just before the -yne suffix.!
Nomenclature of Alkynes (Common Names)!
Nomenclature of Alkynes (Common Names)! Nomenclature of Alkynes (Common Names)!
Nomenclature of Alkynes (Common Names)! 10.3 Acidity of Terminal Alkynes!
• Acetylene is 19 pKa units more acidic than ethylene, which is 1019 times stronger.!
4!
Acidity of Terminal Alkynes: Conjugate Base Stability! Acidity of Terminal Alkynes: Conjugate Base Stability!
25% s! 33% s! 50% s!
Equilibrium! Equilibrium!
Keq = 10(38-25) = 1013!!
Equilibrium! Equilibrium!
Keq = 10(15.7–25) = 10–9.3!!
5!
Alkynide! pKa Table!
10.4 Preparation of Alkynes! Preparation of Alkynes: A Geminal Dihalide!
Preparation of Alkynes: A Vicinal Dihalide! Preparation of Alkynes: Sodium Amide (NaNH2) _ Two Eliminations +!
6!
10.5 Reduction of Alkynes! Hydrogenation of Alkenes – Syn Addition!
Hydrogenation of Alkenes – Syn Addition!
cis-Alkene!
Hydrogenation of Alkenes – Syn Addition!
cis-Alkene!!
k1 < k2!!
v difficult to isolate the intermediate cis-alkene!
k1! k2!
Hydrogenation of Alkenes – Lindlar’s Catalyst! Poisoned Catalyst, e.g. Lindlar’s Catalyst: Controlled Reduction!
7!
Poisoned Catalyst, e.g. Lindlar’s Catalyst – cis Alkene! Reduction of Alkynes: Dissolving Metal Reduction!
What about trans Alkenes?!!
Dissolving metal reduction"
Reduction of Alkynes!
What about trans Alkenes?!!
Dissolving metal reduction"
• Dissolving metal conditions can give anti addition producing the trans alkene.!
• Ammonia has a boiling point of –33°C, so the temperature for these reactions must remain very low.!
• Why can’t water be used as the solvent?!
Reduction of Alkynes!
What about trans Alkenes?!!
Dissolving metal reduction"
• Dissolving metal conditions can give anti addition producing the trans alkene.!
• Ammonia has a boiling point of –33°C, so the temperature for these reactions must remain very low.!
• Why can’t water be used as the solvent?!
Reduction of Alkynes!
What about trans Alkenes?!!
Dissolving metal reduction"
• Dissolving metal conditions can give anti addition producing the trans alkene.!
• Ammonia has a boiling point of –33°C, so the temperature for these reactions must remain very low.!
• Why can’t water be used as the solvent?!
Reduction of Alkynes to trans Alkenes: Dissolving metal reduction!
8!
Sodium Metal Serves as a Source of Electrons! Dissolving Metal Reduction: Arrow !
Dissolving Metal Reduction !
Dissolving Metal Reduction !
Dissolving Metal Reduction !
Dissolving Metal Reduction !
9!
Dissolving Metal Reduction !
Do the pKa values for NH3 and the alkene favor the proton transfer?!!
Dissolving Metal Reduction !
Summary: Catalytic Hydrogenation vs. Dissolving Metal Reduction! Summary: Catalytic Hydrogenation vs. Dissolving Metal Reduction!
Summary: Catalytic Hydrogenation vs. Dissolving Metal Reduction! 10.6 Hydrohalogenation of Alkynes: Markovnikov Addition!
10!
Hydrohalogenation of Alkynes: Markovnikov Addition! A Mechanism For Hydrohalogenation!
A Mechanism For Hydrohalogenation! A Mechanism For Hydrohalogenation: Regioselectivity!
A Mechanism For Hydrohalogenation: Regioselectivity!
Anyway, vinyl carbocations are not particularly stable species. !
A Mechanism For Hydrohalogenation: Regioselectivity!
• Kinetic studies on the hydrohalogenation of an alkyne suggest that the rate law is 1st order with respect to the alkyne, and 2nd order with respect to HX.!
• Termolecular!
11!
Hydrohalogenation of Alkynes: Markovnikov (termolecular)! Hydrohalogenation of Alkynes: Markovnikov Addition!
Hydrohalogenation of Alkynes: Radical Addition – Anti–Markovnikov!
vs.!
Hydrohalogenation of Alkynes: Radical Addition – Anti–Markovnikov!
Interconversion of Alkynes and Dihalides! 10.7 Hydration of Alkynes!
1. Acid-catalyzed hydration: Markovnikov!
2. Hydroboration: Anti–Markovnikov!
12!
Hydration of Alkenes!
1. Acid-catalyzed hydration: Markovnikov!
2. Hydroboration: Anti–Markovnikov!
Hydration of Alkynes!
1. Acid-catalyzed hydration: Markovnikov!
2. Hydroboration: Anti–Markovnikov!
Hydration of Alkynes!
1. Acid-catalyzed hydration: Markovnikov!
2. Hydroboration: Anti–Markovnikov!
Acid-catalyzed keto-enol tautomerization.!Tautomers (enol and ketone) are constitutional isomers.!
Hydration of Alkynes!
1. Acid-catalyzed hydration: Markovnikov!
2. Hydroboration: Anti–Markovnikov!
Hydration of Alkynes!
1. Acid-catalyzed hydration: Markovnikov!
2. Hydroboration: Anti–Markovnikov!
Hydration of Alkynes: Double Hydroboration (Small Boron Reagent)!
1. Acid-catalyzed hydration: Markovnikov!
2. Hydroboration: Anti–Markovnikov!
• Undesired second addition can take place.!
• To block out the second unit of BH3 from reacting with the intermediate, bulky borane reagents are often used.!
13!
Hydration of Alkynes: Double Hydroboration (Small Boron Reagent)!
1. Acid-catalyzed hydration: Markovnikov!
2. Hydroboration: Anti–Markovnikov!
Hydration of Alkynes: Controlling the Regiochemistry!
1. Acid-catalyzed hydration: Markovnikov!
2. Hydroboration: Anti–Markovnikov!
10.8 Halogenation of Alkynes!
• Two equivalents of halogen can be added.!
Halogenation of Alkynes!
10.9 Ozonolysis of Alkynes! Ozonolysis of Alkynes!
14!
10.10 Alkylation of Terminal Alkynes! Alkylation of Terminal Alkynes via SN2!
• The alkynide ion can attack a methyl or 1° alkyl halide electrophile.!
• Alkynide ions usually act as bases with 2° or 3° alkyl halides to cause elimination rather than substitution.!
Alkylation of Terminal Alkynes via SN2!
• Such reactions can be used to develop molecular complexity.!
Application of Alkylation of Terminal Alkynes via SN2!
• Acetylene can be used to perform a double alkylation.!
10.11 Synthesis Strategies! Synthesis Strategies!
15!
Synthesis Strategies! Synthesis Strategies!
Practice!
![Chapter 3: Alkenes and Alkynes - Oneontaemployees.oneonta.edu/odagomo/Chapter_3-L1[1].pdfChapter 3: Alkenes and Alkynes 1 . Hydrogenation of Alkenes and Alkynes Hydrocarbons that have](https://img.dokumen.tips/doc/110x75/5aa8640d7f8b9a7c188b896b/chapter-3-alkenes-and-alkynes-1pdfchapter-3-alkenes-and-alkynes-1-hydrogenation.jpg)
