CHEM 227: CHAPTER 9
35 Cards in this Set
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Ways to classify alkynes
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symmetrical
unsymmetrical
terminal
internal
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Symmetrical alkyne
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2 sides of triple bond equal
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unsymmetrical alkyne
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2 sides of triple bond are unequal
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Terminal alkyne
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at end of molecule
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Internal alkyne
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within a molecule
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R or R' groups can be
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-alkyl group
-aryl/phenyl/benzene group
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Conformation of alkynes
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no cis or trans
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Smallest cyclic alkyne
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cyclooctyne
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Pi bond 1 energy
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216
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Pi bond 2 energy
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208
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Naming alkynes
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same rules as alkene
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If both an alkene & alkyne, number Cs by
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- closest to end is 1
- if equidistant, double bond gets 1
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Reaction of alkyne & X2
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adds in anti fashion
adds twice
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If only 1 mol X2 available in reaction, it adds
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only once across triple bond
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Adding HX + alkyne
Terminal
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adds 2x across triple bond
adds anti
X adds to poor C
H adds to rich C
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Adding HX + alkyne
Internal Unsymmetrical
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adds anti
adds 2x
forms 2 products
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Adding HX + alkyne
Internal Symmetrical
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adds anti
adds 2x
forms 1 product since the two products are the same
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Adding H2 + alkyene, need:
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catalyst - HgSO4 & BH3
adds once
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Adding H2 + alkyene
Terminal
HgSO4
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forms enol
then ketone
Rich C -> CH3
Poor C -> C=O
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Adding H2 + alkyene
Terminal
BH3
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adds once across bond
makes aldehyde
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Adding H2 + alkyene Internal
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either reagent
makes enol then ketone
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Reduction of alkynes
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adds H2 across bond once or twice depending on catalyst to get alkene or alkane
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Reduction using metal catalyst
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H2 adds twice syn forms alkane
total reduction
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Reduction using Lindlar's catalyst
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adds H2 once syn
partial reduction forms cis alkene
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Reduction using NH3
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use Li or Ni as reagent
adds H2 once anti to get a trans alkene
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Oxidative cleavage of alkynes
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By use of KMnO4 or O3
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Oxidative Cleavage of Alkynes
Terminal alkyne
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Terminal C -> CO2
Other C -> COOH
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Oxidative Cleavage
Internal
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both Cs -> COOH
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Acidity of terminal H
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pKa = 25 - weak acid
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Acidity of terminal H of alkyne ___ than alkene and alkane
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more acidic
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To abstract terminal acidic H, use
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strong base
NaNH2 or NaH
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In alkylation of terminal alkyne,
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add NaH to get carbocation
then add alkyl group with X on end
get longer chain as a result
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To convert alkene to alkyne...
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treat with Br
treat with strong base
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Converting to alkyl halide to alkene
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add strong base
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Calculating IDH
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- compare A & product, find pi bonds of product
- decide if alkene or alkyne, if treated with O3 get aldehyde or ketone -> alkene if get COOH & CO2 -> alkyne
- if alkene -> find structure by connecting Os
- if alkyne -> terminal or internal? if terminal, treat w/ NaH & alkyl hali…
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CHEM 227: CHAPTER 9