Ch. 7: The Reactions of Alkynes

Question 1

What is an alkyne?

Answer 1

An alkyne is a hydrocarbon that contains a carbon-carbon triple bond.

Question 2

A (1) ______________ has the triple bond at the end of the chain; an (2) _________ has the triple bond located elsewhere along the chain.

Answer 2

(1) terminal alkyne

(2) internal alkyne

Question 3

Alkynes undergo _____________ reactions. The same reagents that add to alkenes also add to alkynes.

Answer 3

electrophilic addition

Question 4

Are alkynes more or less reactive than alkenes?

Answer 4

Alkynes are less reactive than alkenes.

Question 5

If excess reagent is available, alkynes undergo a second addition reaction with
(1) __________ and (2) __________ because the product of the first reaction is an alkene.

Answer 5

(1) hydrogen halides

(2) halogens

Question 6

The product of the reaction of an alkyne with water under acidic conditions is an
(1) _____ , which immediately rearranges to a (2) ________ . Terminal alkynes require a (3) ___________ .

Answer 6

(1) enol
(2) ketone
(3) mercuric ion catalyst

Question 7

The ketone and enol are called ___________ ; they differ in the location of a double bond and a hydrogen. The keto tautomer usually predominates at equilibrium.

Answer 7

keto-enol tautomers

Question 8

What is interconversion of the tautomers called?

Answer 8

Interconversion of the tautomers is called tautomerization or keto-enol interconversion.

Question 9

Hydroboration-oxidation of an internal alkyne forms a (1) __________ ; hydroboration-oxidation of a terminal alkyne forms an (2) __________ .
Either (3) ______ or (4) _______ can be used for internal alkynes; (5) ______ should be used for terminal alkynes.

Answer 9

(1) ketone
(2) aldehyde
(3) BH3
(4) R2BH
(5) R2BH

Question 10

Catalytic hydrogenation of an alkyne forms an _________ .

Answer 10

alkane

Question 11

Catalytic hydrogenation with Lindlar catalyst converts an internal alkyne to a __________ .

Answer 11

cis alkene

Question 12

Sodium in liquid ammonia converts an internal alkyne to a _____________ .

Answer 12

trans alkene

Question 13

Electronegativity decreases in the order ________________ , so ethyne is a stronger acid than ethene, and ethene is a stronger acid than ethane.

Answer 13

sp > sp2 > sp3

Question 14

An amide ion removes a proton from an sp carbon of a terminal alkyne to form an ______________.

Answer 14

acetylide ion

Question 15

An acetylide ion can undergo an alkylation reaction with a (1) __________ or a
(2) ____________ to form an alkyne.

Answer 15

(1) methyl halide

(2) primary alkyl halide

Question 16

An ________________ attaches an alkyl group to a species.

Answer 16

alkylation reaction

Question 17

Designing a synthesis by working backward is called _________________ .

Answer 17

retrosynthetic analysis