1. Alkyne and Reactions Nomenclature of alkynes
Synthesis of alkyne through elimination rxn
Reactions of alkyne for regioselective synthesis of ketone/aldehyde
Reactions of alkyne for stereospecific synthesis of alkenes
Alkylation of alkyne for synthesis of elongated hydrocarbons
Halogenation and Ozonolysis of alkyne

2. CC Bonding in Alkynes
CC triple bond = Two π bond + ONE  bond, can not rotate.
CC triple bond assumes linearity thus rigidity of molecule.

3. Alkynes: Nucleophile
The presence of two pi bonds and their associated electron density, alkynes are similar to alkenes as a nucleophile (albeit poor)
Converting pi bonds to sigma bonds generally makes a molecule more stable.

4. Alkynes in Nature and Medicine
Acetylene (HCCH) prepared from CaC2 and water, used in blow torches and as a precursor for synthesis
>1,000 different natural alkyne products
Histrionicotoxin, isolated from South American frogs, used on poison-tipped arrows by South American tribes
Ethynylestradiol is the active ingredient in many birth control pills

5. 1. Alkyne Nomenclature
Alkynes are named using the same procedure we used to name alkenes without E/Z or cis/trans
Identify the parent chain, which should include the CC triple bond
Identify and Name the substituents
Assign a locant (and prefix if necessary) to each substituent giving the CC triple bond the lowest number possible
List the numbered substituents before the parent name in alphabetical order. Ignore prefixes (except iso) when ordering alphabetically
The CC triple bond locant is placed either just before the parent name or just before the -yne suffix

6. Identify the longest chain with CC
Identify the parent chain, which should include the CC triple bond
Identify and name the substituents.

7. Triple bond has highest priority
Assign a locant (and prefix if necessary) to each substituent giving the CC triple bond the lowest number possible
The locant is ONE number, NOT two. Although the triple bond bridges carbons 2 and 3, the locant is the lower of those two numbers

8. Finally the Substituents
List the numbered substituents before the parent name in alphabetical order. Ignore prefixes (except iso) when ordering alphabetically
The CC triple bond locant is placed either just before the parent name or just before the -yne suffix

9. Non-IUPAC names
In addition to the IUPAC naming system, chemists often use common names that are derived from the common parent name acetylene
Terminal vs. Internal:
Practice with SkillBuilder 10.1

10. Practice: Alkyne Nomenclature
Name the molecule below
Note: The triple bonds should be drawn as linear
1-cyclohexyl-3-ethyl-3,4-dimethyl-1-pentyne
Or 1-cyclohexyl-3-ethyl-3,4-dimethylpent-1-yne

11. Alkyne Acidity
terminal alkynes have a lower pKa than other hydrocarbons (the sp hybridization of carbanion)
Strong bases (Sodium amide NaNH2, n-butyllithium (n-BuLi), NaH are often used to deprotonate terminal alkyne

12. 2. Sythesis of Alkynes
Like alkenes, alkynes can also be prepared by elimination of dihalogenated alkanes.

13. Elimination of Dihalogenated Alkanes
Memorized the following rxns:
Geminal dihalides can be used
Vicinal dihalides can also be used

14. Elimination and Protonation
Often, excess equivalents of NaNH2 are used to shift the equilibrium toward the elimination products
Finally protonation by stronger acid such as water:

15. Practice: Predict Product/Find Reactant

16. 3. Hydrogenation of Alkyne
Like alkenes, alkynes can readily undergo hydrogenation
Two equivalents of H2 are consumed for each alkynealkane conversion
The cis alkene is the intermediate, like syn addition for alkene.

17. Alkyne to Z-alkene: Lindlar’s Catalyst
A deactivated or poisoned catalyst can be used to selectively convert alkyne to Z-alkene.
Lindlar’s catalyst and P-2 (Ni2B complex) are common examples of a poisoned catalysts

18. Alkyne to E-alkene: Na/NH3(l)
Synthesis of E-alkene: dissolving metal conditions can give E-alkene addition producing the trans alkene
The low boiling point of ammonia (-33°C) requires low temperature

19. Practice: Reduction of Alkyne
Predict the product(s) for the following reaction

20. Hydrogenation: Alkyne & Alkene

21. 4. Hydrohalogenation of Alkynes
Like alkenes, alkynes also undergo hydrohalogenation
Markovnikov regioselectivity: Gemini-dihalogenated alkane

22. Anti-Markovnikov addition
Similar to alkene, peroxides can be used in the hydrohalogenation of alkynes to promote anti-Markovnikov addition just like with alkenes
The process proceeds through a free radical mechanism

23. 5. Hydration with Hg2+ catalyst
Like alkenes, alkynes can also undergo acid catalyzed Markovnikov hydration to form enol (intermediate), which eventually leads to ketone.
The process is generally catalyzed with HgSO4 to compensate for the slow reaction rate that results from the formation of vinylic carbocation

24. Enol/Ketone Tautomerization
The enol intermediate rapidly tautomerizes to form ketone. This equilibrium greatly favors ketone.
Tautomers are constitutional isomers that rapidly interconvert. Tautomerization differs from Resonance.

25. Anti-Markovnikov Hydration: Hydroboration-Oxidation
Hydroboration-oxidation for alkynes proceeds through the same mechanism as for alkenes giving the anti-Markovnikov product
It also produces an enol that will quickly tautomerize to form aldehyde.
Tautomerization is catalyzed by base (OH-)

26. Issues with Hydroboration-Oxidation
After the –BH2 and –H groups have been added across the C=C double bond, in some cases, an 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

27. Bulky boranes for Hydroboration-Oxidation
Some bulky borane reagents are shown below

28. Practice: Hydroboration-Oxidation
Predict products for the following reaction: Markovnikov or otherwise?

29. Hydration Regioselectivity
Markovnikov hydration always leads to a ketone
Anti-Markovnikov hydration of terminal alkyne leads to an aldehyde:

30. Practice: alkyne to carbonyl compd
Draw the alkyne reactant and reagents that could be used to synthesize the following molecule:
Markovnikov pathway?
Anti-Markovnikov pathway?

31. 6. Alkyne Halogenation Alkynes can also undergo halogenation
Two equivalents of halogen can be added

32. 7. Alkyne Ozonolysis
When alkynes react under ozonolysis conditions, the pi system is completely broken, forming carboxylic acid or CO2 (for terminal alkyne)
The molecule is cleaved, and the alkyne carbons are fully oxidized

33. Predict products for Alkyne Ozonolysis

34. 10.10 Alkylation of Terminal Alkynes
Important rxn for synthesis of elongated hydrocarbons!
Deprotonation of terminal alkynes
As acids, terminal alkynes are quite weak
Yet, with a strong enough base, a terminal alkyne can be deprotonated and converted into a good nucleophile

35. Alkylation of Terminal Alkynes: SN2
The alkynide ion can attack a methyl or 1° alkyl halide electrophile
Such reactions can be used to develop molecular complexity
This rxn doesn’t work with 2° or 3° alkyl halides, instead cause elimination (-HX) rather than substitution

36. Double alkylation of acetylene
Acetylene can be used to perform a double alkylation
Note: Reagent NaNH2 and RX need to be added sequentially, not simultaneously
Complex target molecules can be made by building a carbon skeleton and converting functional groups

37. ***Organize your notes
Substrate
Reagent/solvent, steps involved
Key Rxn Intermediate
Main product(s)
Regioselectivity, Stereoselectivity
HgSO4, H2SO4, H2O
Markovniknov

38. Synthetic: Increase saturation
Recall the methods for increasing the saturation of alkenes and alkynes

39. Synthesis: Decrease saturation
Halogenation of an alkene followed by two dehydrohalogenation reactions can decrease saturation
Chapter 11 and 8B will discuss how to convert an alkane into an alkene, but here is a preview

40. Overview of Change in Saturation
In the alkene to alkyne conversion above, why is water needed in part 3) of that reaction?

41. **Example 1: Synthetic Strategies
Give necessary reaction conditions for the multi-step conversions below
Thinking from the End, like planning your future 
1. Reagent(s)/solvent/temperautre will give the final product
Recall the addition reactions of alkene in chapter 9.
2. What is the regioselectivity and stereochemistry for that reagent?
Markovnikov or anti-Markovnikov; Syn vs. Anti

42. Example 1: Synthetic Strategies
(continued) Give necessary reaction conditions for the multi-step conversions below
3. What should be the stereochemistry of substrate (alkene) to give the final product?
Because of the stereospecificity of reagent, certain stereoisomer of substrate is required. If substrate is alkene, which one (E or Z) is required?
4. How to convert the starting material alkyne to the substrate alkene?
Two hydrogenation methods give different alkene stereoisomers

43. Example 2: Synthetic Strategies
Give necessary reaction conditions for the multi-step conversions below
Thinking from the End
1. Reagent(s)/solvent/temperautre will give the final product
Recall the preparation of alkynes
2. What is the regioselectivity and stereochemistry for that reagent?
If applicable

44. Example 2: Synthetic Strategies
Give necessary reaction conditions for the multi-step conversions below
3. What should be the stereochemistry of substrate (dihalide) to give the final product?
Because of the stereospecificity of reagent, certain isomer of substrate is required. If substrate is dihalide, which one (geminal or vicinal) can be prepared from starting material alkene.
4. How to convert the starting material alkene to the substrate dihalide?
Markovnikov or anti-Markovnikov hydrohalogenation.

45. Additional Practice Problems
Name the molecule
Draw the structure of 2,2-dimethyl-6-chloro-3-heptyne

46. Additional Practice Problems
Give 2 sets of reagents that could be used to synthesize 1-pentyne through elimination reactions.

47. Additional Practice Problems
Give a set of reagents that could be used to synthesize cis-2-pentene from an addition reaction.
Give a set of reagents that could be used to synthesize trans-2-pentene from an addition reaction.

48. Additional Practice Problems
Give a set of reagents that could be used to synthesize a ketone from an addition reaction.
Give a set of reagents that could be used to synthesize an aldehyde from an addition reaction.

49. Additional Practice Problems
Determine necessary reagents to complete the synthesis below.

50. Protonation after Elimination
A proton source is needed to produce the alkyne
Practice: Predict the products in the example below

51. Practice: Dissolving Metal Reductions
Predict the product(s) for the following reaction