Nucleophilic Substitution
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Nucleophilic SubstitutionNucleophilic Substitution
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Functional Group Functional Group
Transformation By Nucleophilic Transformation By Nucleophilic
SubstitutionSubstitution
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Y Y ::––
RR XX YY RR++ ++ : : XX––
nucleophilenucleophile is a Lewis base (electron-pair donor) is a Lewis base (electron-pair donor)
often negatively charged and used as often negatively charged and used as NaNa++ or K or K++ salt salt
substrate is usually an substrate is usually an alkylalkyl halidehalide
Nucleophilic SubstitutionNucleophilic Substitution
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Substrate cannot be an a vinylic halide or anSubstrate cannot be an a vinylic halide or anaryl halide, except under certain conditionsaryl halide, except under certain conditions
XX
CCCC
XX
Nucleophilic SubstitutionNucleophilic Substitution
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++ RR XX
gives an ethergives an ether
Alkoxide ion as the nucleophileAlkoxide ion as the nucleophile
....OO::
....R'R'
––
++ : : XXRR....OO....
R'R' ––
Examples of Nucleophilic SubstitutionExamples of Nucleophilic Substitution
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(CH(CH33))22CHCHCHCH22ONa + CHONa + CH33CHCH22BrBr
Isobutyl alcoholIsobutyl alcohol
(CH(CH33))22CHCHCHCH22OCHOCH22CHCH33 + NaBr + NaBr
Ethyl isobutyl ether (66%)Ethyl isobutyl ether (66%)
ExampleExample
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++ RR XX
gives an estergives an ester
Carboxylate ion as the nucleophileCarboxylate ion as the nucleophile
....OO::
....R'CR'C
––
++ : : XXRR....OO....
R'CR'C ––
OO
OO
Examples of Nucleophilic SubstitutionExamples of Nucleophilic Substitution
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OKOK ++CHCH33(CH(CH22))1616CC CHCH33CHCH22II
acetone, wateracetone, water
++ KIKIOO CHCH22CHCH33CHCH33(CH(CH22))1616CC
Ethyl octadecanoate (95%)Ethyl octadecanoate (95%)
OO
OO
ExampleExample
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++ RR XX
gives a thiolgives a thiol
Hydrogen sulfide ion as the nucleophileHydrogen sulfide ion as the nucleophile
....SS::
....HH
––
++ : : XXRR....SS....
HH ––
Examples of Nucleophilic SubstitutionExamples of Nucleophilic Substitution
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KSH + CHKSH + CH33CH(CHCH(CH22))66CHCH33
BrBr
ethanol, waterethanol, water
+ KBr+ KBr
2-Nonanethiol (74%)2-Nonanethiol (74%)
CHCH33CH(CHCH(CH22))66CHCH33
SHSH
ExampleExample
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++ RR XX
gives a nitrilegives a nitrile
Cyanide ion as the nucleophileCyanide ion as the nucleophile
––
++ : : XXRR ––
CCNN:: ::
CCNN::
Examples of Nucleophilic SubstitutionExamples of Nucleophilic Substitution
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DMSODMSO
Cyclopentyl cyanide (70%)Cyclopentyl cyanide (70%)
BrBrNaCNNaCN ++
CNCN
++ NaCNNaCN
ExampleExample
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++ RR XX
gives an alkyl azidegives an alkyl azide
Azide ion as the nucleophileAzide ion as the nucleophile
++ : : XXRR ––
....––
NN NN NN.... ::::–– ++
....NN NN NN....::–– ++
Examples of Nucleophilic SubstitutionExamples of Nucleophilic Substitution
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NaNNaN33 + CH + CH33CHCH22CHCH22CHCH22CHCH22II
2-Propanol-water2-Propanol-water
CHCH33CHCH22CHCH22CHCH22CHCH22NN33 + NaI + NaI
Pentyl azide (52%)Pentyl azide (52%)
ExampleExample
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++ RR XX
gives an alkyl iodidegives an alkyl iodide
Iodide ion as the nucleophileIodide ion as the nucleophile
++ : : XXRR ––
––
....:: II
....
....:: II
....::
Examples of Nucleophilic SubstitutionExamples of Nucleophilic Substitution
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NaI is soluble in acetone; NaI is soluble in acetone; NaCl and NaBr are not NaCl and NaBr are not soluble in acetone.soluble in acetone.
acetoneacetone
++ NaINaICHCH33CHCHCHCH33
BrBr
63%63%
++ NaBrNaBrCHCH33CHCHCHCH33
II
ExampleExample
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Relative Reactivity of Halide Relative Reactivity of Halide Leaving GroupsLeaving Groups
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RIRI
RBrRBr
RClRCl
RFRF
most reactivemost reactive
least reactiveleast reactive
GeneralizationGeneralization
Reactivity of halide leaving groups in Reactivity of halide leaving groups in nucleophilic substitution is the same as nucleophilic substitution is the same as for elimination.for elimination.
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BrBrCHCH22CHCH22CHCH22ClCl + Na + NaCNCN
A single organic product was obtained when A single organic product was obtained when 1-bromo-3-chloropropane was allowed to react 1-bromo-3-chloropropane was allowed to react with one molar equivalent of sodium cyanide in with one molar equivalent of sodium cyanide in aqueous ethanol. What was this product?aqueous ethanol. What was this product?
Br is a better leaving Br is a better leaving group than Clgroup than Cl
ProblemProblem
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BrBrCHCH22CHCH22CHCH22ClCl + Na + NaCNCN
A single organic product was obtained when A single organic product was obtained when 1-bromo-3-chloropropane was allowed to react 1-bromo-3-chloropropane was allowed to react with one molar equivalent of sodium cyanide in with one molar equivalent of sodium cyanide in aqueous ethanol. What was this product?aqueous ethanol. What was this product?
CHCH22CHCH22CHCH22ClCl + Na + NaBrBrCCNN::
ProblemProblem