Chapter 7.5: Preparation of Alkynes
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Define allene
the compound CH2=C=CH2. Any compound that contains adjacent carbon-carbon double bonds; that is, any molecule that contains a C=C=C functional group
Describe the mechanism of preparing a alkyne from an alkene
o To prepare an alkyne from an alkene, the alkene is first treated with one mole of either bromine (Br2) or chlorine (Cl2) to give a dihaloalkane o Treating the dihaloalkane with two moles of a strong base such as sodium amide (NaNH2) in liquid ammonia [NH3(l)] brings about two successive dehydrohalogenations o In dehydrogenation of a haloalkene with at least one hydrogen on each adjacent carbon, a side reaction occurs, namely the formation of an allene
What is removal of -H and -X from adjacent carbons?
dehydrohalogenation
Define internal alkyne
a carbon-carbon triple bond in the middle of a carbon chain
What is a carbon-carbon triple bond in the middle of a carbon chain?
internal alkyne
What is any reaction in which a new carbon-carbon bond to an alkyl group is formed?
alkylation reaction
Define alkylation reaction
any reaction in which a new carbon-carbon bond to an alkyl group is formed
What are the reagents for alkylation of acetylide anions?
acetylide anions, methyl and 1° Haloalkanes
What are the reagents involved in preparing an alkyne from an alkene?
• Br2 or Cl2 2. NaNH2/NH3(l)
Define dehydrohalogenation
removal of -H and -X from adjacent carbons
Describe the mechanism of nucleophilic substitution for • Alkylation of Acetylide Anions with Methyl and 1° Haloalkanes
An acetylide anion is a nucleophile and donates its unshared pair of electrons to the carbon of a methyl or primary haloalkane The acetylide nucleophile replaces the halogen atom
What is the compound CH2=C=CH2. Any compound that contains adjacent carbon-carbon double bonds; that is, any molecule that contains a C=C=C functional group?
allene