Chapter 7.5: Preparation of Alkynes

Question 1

Define allene

Answer 1

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

Question 2

Describe the mechanism of preparing a alkyne from an alkene

Answer 2

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

Question 3

What is removal of -H and -X from adjacent carbons?

Answer 3

dehydrohalogenation

Question 4

Define internal alkyne

Answer 4

a carbon-carbon triple bond in the middle of a carbon chain

Question 5

What is a carbon-carbon triple bond in the middle of a carbon chain?

Answer 5

internal alkyne

Question 6

What is any reaction in which a new carbon-carbon bond to an alkyl group is formed?

Answer 6

alkylation reaction

Question 7

Define alkylation reaction

Answer 7

any reaction in which a new carbon-carbon bond to an alkyl group is formed

Question 8

What are the reagents for alkylation of acetylide anions?

Answer 8

acetylide anions, methyl and 1° Haloalkanes

Question 9

What are the reagents involved in preparing an alkyne from an alkene?

Answer 9

1. Br2 or Cl2

2. NaNH2/NH3(l)

Question 10

Define dehydrohalogenation

Answer 10

removal of -H and -X from adjacent carbons

Question 11

Describe the mechanism of nucleophilic substitution for • Alkylation of Acetylide Anions with Methyl and 1° Haloalkanes

Answer 11

 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

Question 12

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?

Answer 12

allene