EXAM 4
Learning Objectives – Chapter 9, Chapter 10, and Chapter 11
CHAPTER 9 – ALKYNES (C ≡ C)
1. Use IUPAC systematic nomenclature to name alkynes
I. Identify the parent chain, à include the C≡C triple bond(even if withouth it is longer)
II. Identify and name the substituents
III. Assign a locant (and prefix if necessary) to each substituent
IV. giving the C ≡C triple bond the lowest number possible
V. List the numbered substituents before the parent name in alphabetical order. Ignore
prefixes (except iso) when ordering alphabetically
VI. The C≡ triple bond locant is placed either just before the parent name or just before
the -yne suffix
VII. Include R/S configuration if any chiral center is present in the structure
• Alkynes classifies as terminal or internal (between more C) (no E/Z isomerism)
2. Describe the relative acidity of terminal alkynes and propose acid-base reactions
in which a terminal alkyne is the acid
- terminal alkynes are + acidic than other hydrocarbons
- Can be deprotonated by a strong base to form conjugate base (acetylide ion/alkyne
anion) à more stable because the lone pair occupies sp orbital (+ s-character/
smaller/ closer to nucleus)
à BASE is usually NaNH2 (can also be
NaH but not t-ButOK)
à conjugate acids muist be pKa>25
Alhynide ion = aceltylide (conjugate base)
3. Describe the preparation of alkynes from alkyl dihalides, including the
mechanism and structure of the final product
NaNH2 (2
equivalents)
àHalides can be on opposite (germinal) or same
sides (vicinal)
à excess NH2 used to shift equilibrium towards
product à H2O is added to produce neutral
alkyne
à overall terminal alkyne is prepared by
treating dihalide w/ 1) excess (xs) NaNH2 &
2)water
, 4. Describe the reduction of alkynes using catalytic hydrogenation or dissolving
metal, including the structure of the final product (not the mechanisms)
Catalytic hydrogenation – alkyne à to an alkane by addition of two equivalents of H2
§ To stop the reaction at the cis alkene: use
INPURE/POISONED/DEACTIVATED catalyst à Lindlar’s catalyst/ Ni2B
complex ((catalyzes 1st addition of H2 but not 2nd)
§ If internal alkene look for cis isomerism (if terminal, no need)
Reduction to a trans alkene: neutral Na & liquid NH3 (ONLY works with internal
alkynes) à anti addition of H & H
!!! SUMMARY REDUCTION OF ALKYNES:
5. Describe hydrohalogenation reaction of alkynes, including the mechanism, effect
of peroxides, and regiochemistry of the product
§ Hydrohalogenation reaction: markovnikov addition of H & Halide to alkyne
à mechanism is unclear since it involves a vinyl carbocation (really unstable)
§ Mechanism: if H-X in excess (xs) à 2 steps repeat and dihalide as product
Learning Objectives – Chapter 9, Chapter 10, and Chapter 11
CHAPTER 9 – ALKYNES (C ≡ C)
1. Use IUPAC systematic nomenclature to name alkynes
I. Identify the parent chain, à include the C≡C triple bond(even if withouth it is longer)
II. Identify and name the substituents
III. Assign a locant (and prefix if necessary) to each substituent
IV. giving the C ≡C triple bond the lowest number possible
V. List the numbered substituents before the parent name in alphabetical order. Ignore
prefixes (except iso) when ordering alphabetically
VI. The C≡ triple bond locant is placed either just before the parent name or just before
the -yne suffix
VII. Include R/S configuration if any chiral center is present in the structure
• Alkynes classifies as terminal or internal (between more C) (no E/Z isomerism)
2. Describe the relative acidity of terminal alkynes and propose acid-base reactions
in which a terminal alkyne is the acid
- terminal alkynes are + acidic than other hydrocarbons
- Can be deprotonated by a strong base to form conjugate base (acetylide ion/alkyne
anion) à more stable because the lone pair occupies sp orbital (+ s-character/
smaller/ closer to nucleus)
à BASE is usually NaNH2 (can also be
NaH but not t-ButOK)
à conjugate acids muist be pKa>25
Alhynide ion = aceltylide (conjugate base)
3. Describe the preparation of alkynes from alkyl dihalides, including the
mechanism and structure of the final product
NaNH2 (2
equivalents)
àHalides can be on opposite (germinal) or same
sides (vicinal)
à excess NH2 used to shift equilibrium towards
product à H2O is added to produce neutral
alkyne
à overall terminal alkyne is prepared by
treating dihalide w/ 1) excess (xs) NaNH2 &
2)water
, 4. Describe the reduction of alkynes using catalytic hydrogenation or dissolving
metal, including the structure of the final product (not the mechanisms)
Catalytic hydrogenation – alkyne à to an alkane by addition of two equivalents of H2
§ To stop the reaction at the cis alkene: use
INPURE/POISONED/DEACTIVATED catalyst à Lindlar’s catalyst/ Ni2B
complex ((catalyzes 1st addition of H2 but not 2nd)
§ If internal alkene look for cis isomerism (if terminal, no need)
Reduction to a trans alkene: neutral Na & liquid NH3 (ONLY works with internal
alkynes) à anti addition of H & H
!!! SUMMARY REDUCTION OF ALKYNES:
5. Describe hydrohalogenation reaction of alkynes, including the mechanism, effect
of peroxides, and regiochemistry of the product
§ Hydrohalogenation reaction: markovnikov addition of H & Halide to alkyne
à mechanism is unclear since it involves a vinyl carbocation (really unstable)
§ Mechanism: if H-X in excess (xs) à 2 steps repeat and dihalide as product
