dr. wolf's chm 201 & 202 9-1 chapter 9 alkynes. dr. wolf's chm 201 & 202 9-2 9.1...
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Dr. Wolf's CHM 201 & 202 9-1
Chapter 9Chapter 9AlkynesAlkynes
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Dr. Wolf's CHM 201 & 202 9-2
9.19.1Sources of AlkynesSources of Alkynes
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Dr. Wolf's CHM 201 & 202 9-3
AcetyleneAcetyleneAcetyleneAcetylene
Industrial preparation of acetylene isIndustrial preparation of acetylene isby dehydrogenation of ethyleneby dehydrogenation of ethylene
CHCH33CHCH33
800°C800°C
1150°C1150°C
cost of energy makes acetylene a morecost of energy makes acetylene a moreexpensive industrial chemical than ethyleneexpensive industrial chemical than ethylene
HH22CC CHCH22
HH22CC CHCH22 HCHC CHCH
HH22++
HH22++
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Dr. Wolf's CHM 201 & 202 9-4
9.29.2NomenclatureNomenclature
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Dr. Wolf's CHM 201 & 202 9-5
HCHC CHCHAcetylene and ethyne are both acceptableAcetylene and ethyne are both acceptableIUPAC names forIUPAC names for
NomenclatureNomenclatureNomenclatureNomenclature
Higher alkynes are named in much the sameHigher alkynes are named in much the sameway as alkenes except using an -way as alkenes except using an -yneyne suffix suffixinstead of -instead of -eneene..
HCHC CCHCCH33
PropynePropyne
HCHC CCHCCH22CHCH33
1-Butyne1-Butyne
(CH(CH33))33CCCC CCHCCH33
4,4-Dimethyl-2-pentyne4,4-Dimethyl-2-pentyne
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Dr. Wolf's CHM 201 & 202 9-6
9.39.3Physical Properties of AlkynesPhysical Properties of Alkynes
The physical properties of alkynes are The physical properties of alkynes are similar to those of alkanes and alkenes.similar to those of alkanes and alkenes.
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Dr. Wolf's CHM 201 & 202 9-7
9.49.4Structure and Bonding in Alkynes:Structure and Bonding in Alkynes:
spsp Hybridization Hybridization
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Dr. Wolf's CHM 201 & 202 9-8
StructureStructureStructureStructure
linear geometry for acetylenelinear geometry for acetylene
CC CCHH HH
120 pm120 pm
106 pm106 pm 106 pm106 pm
CC CCCHCH33 HH
121 pm121 pm
146 pm146 pm 106 pm106 pm
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Dr. Wolf's CHM 201 & 202 9-9
Cyclononyne is the Cyclononyne is the smallest cycloalkyne smallest cycloalkyne stable enough to be stable enough to be stored at room temperaturestored at room temperaturefor a reasonable length for a reasonable length of time. of time.
Cyclooctyne polymerizesCyclooctyne polymerizeson standing.on standing.
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Dr. Wolf's CHM 201 & 202 9-10
22ss
22pp
22spsp
Mix together (hybridize) the 2s orbital Mix together (hybridize) the 2s orbital and and oneone of the three 2p orbitals of the three 2p orbitals
22pp
Bonding in acetylene is based on Bonding in acetylene is based on spsp-hybridization-hybridizationfor each carbonfor each carbon
Bonding in acetylene is based on Bonding in acetylene is based on spsp-hybridization-hybridizationfor each carbonfor each carbon
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Dr. Wolf's CHM 201 & 202 9-11
22spsp
Mix together (hybridize) the 2s orbital Mix together (hybridize) the 2s orbital and and oneone of the three 2p orbitals of the three 2p orbitals
22pp
Bonding in acetylene is based on Bonding in acetylene is based on spsp-hybridization-hybridizationfor each carbonfor each carbon
Bonding in acetylene is based on Bonding in acetylene is based on spsp-hybridization-hybridizationfor each carbonfor each carbon
Each carbon has two Each carbon has two half-filled half-filled spsp orbitals orbitalsavailable to form available to form bonds. bonds.
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Dr. Wolf's CHM 201 & 202 9-12
Bonds in AcetyleneBonds in Acetylene Bonds in AcetyleneBonds in Acetylene
Each carbon isEach carbon is
connected to aconnected to a
hydrogen by ahydrogen by a
bond. The two bond. The two
carbons are connectedcarbons are connected
to each other by ato each other by a
bond and two bond and two bonds. bonds.
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Dr. Wolf's CHM 201 & 202 9-13
Bonds in AcetyleneBonds in Acetylene Bonds in AcetyleneBonds in Acetylene
One of the twoOne of the two
bonds in bonds in
acetylene isacetylene is
shown here.shown here.
The second The second bond is at rightbond is at right
angles to the first.angles to the first.
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Dr. Wolf's CHM 201 & 202 9-14
Bonds in AcetyleneBonds in Acetylene Bonds in AcetyleneBonds in Acetylene
This is the secondThis is the second
of the twoof the two
bonds in bonds in
acetylene.acetylene.
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Dr. Wolf's CHM 201 & 202 9-15
The region of highest The region of highest
negative charge lies abovenegative charge lies above
and below the molecular and below the molecular
plane in ethylene.plane in ethylene.
The region of highest The region of highest
negative charge encirclesnegative charge encircles
the molecule around itsthe molecule around its
center in acetylene.center in acetylene.
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Dr. Wolf's CHM 201 & 202 9-16
C—C distanceC—C distanceC—C distanceC—C distance
C—H distanceC—H distanceC—H distanceC—H distance
H—C—C anglesH—C—C anglesH—C—C anglesH—C—C angles
C—C BDEC—C BDEC—C BDEC—C BDE
C—H BDEC—H BDEC—H BDEC—H BDE
% % ss character character% % ss character character
ppKKaappKKaa
153 pm153 pm153 pm153 pm
111 pm111 pm111 pm111 pm
111.0°111.0°111.0°111.0°
368 kJ/mol368 kJ/mol368 kJ/mol368 kJ/mol
410 kJ/mol410 kJ/mol410 kJ/mol410 kJ/mol
spsp33spsp33
25%25%25%25%
62626262
134 pm134 pm134 pm134 pm
110 pm110 pm110 pm110 pm
121.4°121.4°121.4°121.4°
611 kJ/mol611 kJ/mol611 kJ/mol611 kJ/mol
452 kJ/mol452 kJ/mol452 kJ/mol452 kJ/mol
spsp22spsp22
33%33%33%33%
45454545
120 pm120 pm120 pm120 pm
106 pm106 pm106 pm106 pm
180°180°180°180°
820 kJ/mol820 kJ/mol820 kJ/mol820 kJ/mol
536 kJ/mol536 kJ/mol536 kJ/mol536 kJ/mol
spspspsp
50%50%50%50%
26262626
hybridization of Chybridization of Chybridization of Chybridization of C
Table 9.1 Comparison of ethane, ethylene, and acetyleneTable 9.1 Comparison of ethane, ethylene, and acetylene
Ethane Ethylene Ethane Ethylene AcetyleneAcetylene
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Dr. Wolf's CHM 201 & 202 9-17
9.59.5
Acidity of Acetylene andTerminal AlkynesAcidity of Acetylene andTerminal Alkynes
HH
CC CC
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Dr. Wolf's CHM 201 & 202 9-18
In general, hydrocarbons are In general, hydrocarbons are exceedingly weak acidsexceedingly weak acids
In general, hydrocarbons are In general, hydrocarbons are exceedingly weak acidsexceedingly weak acids
CompoundCompound ppKKaa
HFHF 3.23.2
HH22OO 1616
NHNH33 3636
4545
CHCH44 6060
HH22CC CHCH22
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Dr. Wolf's CHM 201 & 202 9-19
Acetylene is a weak acid, but not nearlyAcetylene is a weak acid, but not nearlyas weak as alkanes or alkenes.as weak as alkanes or alkenes.
Acetylene is a weak acid, but not nearlyAcetylene is a weak acid, but not nearlyas weak as alkanes or alkenes.as weak as alkanes or alkenes.
CompoundCompound ppKKaa
HFHF 3.23.2
HH22OO 1616
NHNH33 3636
4545
CHCH44 6060
HH22CC CHCH22
HCHC CHCH 26262626
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Dr. Wolf's CHM 201 & 202 9-20
Electronegativity of carbon Electronegativity of carbon increases with its increases with its ss character character
Electronegativity of carbon Electronegativity of carbon increases with its increases with its ss character character
CC HH HH++ ++
HH++ ++
HH++ ++
1010-60-60
1010-45-45
1010-26-26
sp3sp3CC :
sp2sp2
spsp
HH
CC CC
CC CC HH
CC CC
CC CC :
:
Electrons in an orbital with more Electrons in an orbital with more ss character are closer to the character are closer to the
nucleus and more strongly held.nucleus and more strongly held.
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Dr. Wolf's CHM 201 & 202 9-21
Objective:Objective:Prepare a solution containing sodium acetylidePrepare a solution containing sodium acetylide
Will treatment of acetylene with NaOH be effective?Will treatment of acetylene with NaOH be effective?
Objective:Objective:Prepare a solution containing sodium acetylidePrepare a solution containing sodium acetylide
Will treatment of acetylene with NaOH be effective?Will treatment of acetylene with NaOH be effective?
NaCNaC CHCH
HH22OONaOHNaOH ++ HCHC CHCH NaCNaC CHCH ++
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Dr. Wolf's CHM 201 & 202 9-22
No. Hydroxide is not a strong enough No. Hydroxide is not a strong enough base to deprotonate acetylene.base to deprotonate acetylene.
No. Hydroxide is not a strong enough No. Hydroxide is not a strong enough base to deprotonate acetylene.base to deprotonate acetylene.
HH22OONaOHNaOH ++ HCHC CHCH NaCNaC CHCH ++
––HOHO
....
.... ::
HH CC CHCH HOHO HH....
....++ ++ CC CHCH::––
weaker acidweaker acidppKKaa = 26 = 26
stronger acidstronger acidppKKaa = 16 = 16
In acid-base reactions, the equilibrium lies toIn acid-base reactions, the equilibrium lies tothe side of the weaker acid.the side of the weaker acid.
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Dr. Wolf's CHM 201 & 202 9-23
Solution: Use a stronger base. Sodium amideSolution: Use a stronger base. Sodium amideis a stronger base than sodium hydroxide.is a stronger base than sodium hydroxide.
Solution: Use a stronger base. Sodium amideSolution: Use a stronger base. Sodium amideis a stronger base than sodium hydroxide.is a stronger base than sodium hydroxide.
NHNH33NaNaNHNH22 ++ HCHC CHCH NaCNaC CHCH ++
––HH22NN
....::
HH CC CHCH HH....
++ ++ CC CHCH::––
stronger acidstronger acidppKKaa = 26 = 26
weaker acidweaker acidppKKaa = 36 = 36
Ammonia is a weaker acid than acetylene.Ammonia is a weaker acid than acetylene.The position of equilibrium lies to the right.The position of equilibrium lies to the right.
HH22NN
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Dr. Wolf's CHM 201 & 202 9-24
9.69.6Preparation of Alkynes Preparation of Alkynes
bybyAlkylation of Acetylene and Terminal AlkynesAlkylation of Acetylene and Terminal Alkynes
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Dr. Wolf's CHM 201 & 202 9-25
Preparation of AlkynesPreparation of AlkynesPreparation of AlkynesPreparation of Alkynes
Carbon-carbon bond formationCarbon-carbon bond formationalkylation of acetylene and terminal alkynesalkylation of acetylene and terminal alkynes
Functional-group transformationsFunctional-group transformationseliminationelimination
There are two main methods for the preparationThere are two main methods for the preparationof alkynes:of alkynes:
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Dr. Wolf's CHM 201 & 202 9-26
Alkylation of acetylene and terminal alkynesAlkylation of acetylene and terminal alkynesAlkylation of acetylene and terminal alkynesAlkylation of acetylene and terminal alkynes
H—C H—C C—HC—H
RR—C —C C—HC—H
RR—C —C C—C—RR
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Dr. Wolf's CHM 201 & 202 9-27
RR XXSSNN22
Alkylation of acetylene and terminal alkynesAlkylation of acetylene and terminal alkynesAlkylation of acetylene and terminal alkynesAlkylation of acetylene and terminal alkynes
XX––::++CC––::H—C H—C C—RC—RH—C H—C ++
• The alkylating agent is an alkyl halide, andThe alkylating agent is an alkyl halide, andthe reaction is nucleophilic substitution.the reaction is nucleophilic substitution.
• The nucleophile is sodium acetylide or the The nucleophile is sodium acetylide or the sodium salt of a terminal (monosubstituted) sodium salt of a terminal (monosubstituted) alkyne.alkyne.
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Dr. Wolf's CHM 201 & 202 9-28
Example: Example: Alkylation of acetylene Alkylation of acetylene Example: Example: Alkylation of acetylene Alkylation of acetylene
NaNHNaNH22
NHNH33
CHCH33CHCH22CHCH22CHCH22BrBr
(70-77%)(70-77%)
HCHC CHCH HCHC CCNaNa
HCHC CC CHCH22CHCH22CHCH22CHCH33
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Dr. Wolf's CHM 201 & 202 9-29
NaNHNaNH22, NH, NH33
CHCH33BrBr
Example: Example: Alkylation of a terminal alkyne Alkylation of a terminal alkyne Example: Example: Alkylation of a terminal alkyne Alkylation of a terminal alkyne
CCHH(CH(CH33))22CHCHCHCH22CC
CCNaNa(CH(CH33))22CHCHCHCH22CC
(81%)(81%)
C—CHC—CH33(CH(CH33))22CHCHCHCH22CC
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Dr. Wolf's CHM 201 & 202 9-30
1. NaNH1. NaNH22, NH, NH33
2. 2. CHCH33CHCH22BrBr
(81%)(81%)
Example: Example: Dialkylation of acetyleneDialkylation of acetyleneExample: Example: Dialkylation of acetyleneDialkylation of acetylene
H—C H—C C—HC—H
1. NaNH1. NaNH22, NH, NH33
2. 2. CHCH33BrBr
C—HC—HCHCH33CHCH22—C—C
C—C—CHCH33CHCH33CHCH22—C—C
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Dr. Wolf's CHM 201 & 202 9-31
LimitationLimitationLimitationLimitation
Effective only with primary alkyl Effective only with primary alkyl halideshalides
Secondary and tertiary alkyl halides Secondary and tertiary alkyl halides undergo eliminationundergo elimination
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Dr. Wolf's CHM 201 & 202 9-32
E2 predominates over SE2 predominates over SNN2 when alkyl 2 when alkyl
halide is secondary or tertiaryhalide is secondary or tertiary
E2 predominates over SE2 predominates over SNN2 when alkyl 2 when alkyl
halide is secondary or tertiaryhalide is secondary or tertiary
HH CC
C— C— XX
E2E2
CC––::H—C H—C
++CCH—C H—C ——HH CC CC XX––::++
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Dr. Wolf's CHM 201 & 202 9-33
9.79.7Preparation of Alkynes byPreparation of Alkynes by
Elimination ReactionsElimination Reactions
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Dr. Wolf's CHM 201 & 202 9-34
Preparation of Alkynes by Preparation of Alkynes by "Double" Dehydrohalogenation"Double" Dehydrohalogenation
Preparation of Alkynes by Preparation of Alkynes by "Double" Dehydrohalogenation"Double" Dehydrohalogenation
Geminal dihalideGeminal dihalide Vicinal dihalideVicinal dihalide
XX
CC CC
XX
HH
HH
XX XX
CC CC
HHHH
The most frequent applications are in preparation The most frequent applications are in preparation of terminal alkynes.of terminal alkynes.
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Dr. Wolf's CHM 201 & 202 9-35
Geminal dihalide Geminal dihalide Alkyne AlkyneGeminal dihalide Geminal dihalide Alkyne Alkyne
(CH(CH33))33CCCCHH22—CH—CHClCl22
1. 3NaNH1. 3NaNH22, NH, NH33
2. H2. H22OO
(56-60%)(56-60%)
(CH(CH33))33CCCC CHCH
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Dr. Wolf's CHM 201 & 202 9-36
NaNHNaNH22, NH, NH33
NaNHNaNH22, NH, NH33
NaNHNaNH22, NH, NH33HH22OO
Geminal dihalide Geminal dihalide Alkyne AlkyneGeminal dihalide Geminal dihalide Alkyne Alkyne
(CH(CH33))33CCCCHH22—CH—CHClCl22
(CH(CH33))33CCCCHH CHCHClCl
(CH(CH33))33CCCC CHCH
(CH(CH33))33CCCC CNaCNa
(slow)(slow)
(slow)(slow)
(fast)(fast)
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Dr. Wolf's CHM 201 & 202 9-37
CHCH33(CH(CH22))77CCHH—C—CHH22BrBr
BrBr
Vicinal dihalide Vicinal dihalide Alkyne AlkyneVicinal dihalide Vicinal dihalide Alkyne Alkyne
1. 3NaNH1. 3NaNH22, NH, NH33
2. H2. H22OO
(54%)(54%)
CHCH33(CH(CH22))77CC CHCH
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Dr. Wolf's CHM 201 & 202 9-38
9.89.8Reactions of AlkynesReactions of Alkynes
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Dr. Wolf's CHM 201 & 202 9-39
Reactions of AlkynesReactions of AlkynesReactions of AlkynesReactions of Alkynes
Acidity (Section 9.5)Acidity (Section 9.5)Hydrogenation (Section 9.9)Hydrogenation (Section 9.9)Metal-Ammonia Reduction (Section 9.10)Metal-Ammonia Reduction (Section 9.10)Addition of Hydrogen Halides (Section 9.11)Addition of Hydrogen Halides (Section 9.11)Hydration (Section 9.12)Hydration (Section 9.12)Addition of Halogens (Section 9.13)Addition of Halogens (Section 9.13)Ozonolysis (Section 9.14)Ozonolysis (Section 9.14)
Acidity (Section 9.5)Acidity (Section 9.5)Hydrogenation (Section 9.9)Hydrogenation (Section 9.9)Metal-Ammonia Reduction (Section 9.10)Metal-Ammonia Reduction (Section 9.10)Addition of Hydrogen Halides (Section 9.11)Addition of Hydrogen Halides (Section 9.11)Hydration (Section 9.12)Hydration (Section 9.12)Addition of Halogens (Section 9.13)Addition of Halogens (Section 9.13)Ozonolysis (Section 9.14)Ozonolysis (Section 9.14)