Deck 9: Alkynes: an Introduction to Organic Synthesis

Question 1

Specify the hybridization on the carbons shown in the following structure.

A)1: sp³ 2: sp²
B)1: sp² 2: sp.
C)1: sp³ 2: sp
D)1: sp² 2: sp

Answer 1

1: sp³ 2: sp

Question 2

Draw: 3,10-dimethyl-6-sec-butylcyclodecyne

Answer 2

Question 3

Consider the three structures shown below. Explain why Structure C is unstable

Answer 3

The hybridization on the carbon atoms of the triple bond is sp and produces a bond angle of 180°.This dictates a linear geometry about both carbon atoms of the triple bond.In Structure C the internal bond angles between the sp hybridized carbon atoms and the adjacent sp³ carbon atoms of the ring is much less than 180° (approximately 120°).This compression of the bond angle produces too much strain for the ring to be stable.Puckering of the ring cannot relieve the strain to the degree that is does for Structures A and B.The linear geometry is required to allow for the appropriate orbital overlap to form the sigma bonds between the sp carbon atoms and the sp³ carbon atoms.

Question 4

Exhibit 9-1
The compound below has been isolated from the safflower plant.Consider its structure to answer the following question(s).
​
Refer to Exhibit 9-1.What is the degree of unsaturation for this compound?

Question 5

Exhibit 9-1
The compound below has been isolated from the safflower plant.Consider its structure to answer the following question(s).
​
Refer to Exhibit 9-1.Assign E or Z configuration to each of the double bonds in the compound.

Question 6

Exhibit 9-5
To answer the following question(s) consider this reaction:
​
Refer to Exhibit 9-5.The key intermediate in the electrophilic addition reaction shown above is called:

A)an acetylenic carbocation
B)a vinylic bromide
C)a secondary carbocation
D)a vinylic carbocation

Question 7

Exhibit 9-2
To answer the following question(s),consider the information below:
​
The heat of hydrogenation of 1,4-pentadiene is 254.4 kJ/mol.The heat of hydrogenation of 1-pentyne is approximately 292.9 kJ/mol.
Refer to Exhibit 9-2.Show the energy differences between the hydrogenation of 1,4-pentadiene and 1-pentyne on a reaction energy diagram.

Question 8

Draw: 4-bromo-3,3-dimethyl-1-hexen-5-yne

Question 9

Exhibit 9-5
To answer the following question(s) consider this reaction:
​
Refer to Exhibit 9-5.On the structures provided,draw arrows showing the electron flow for the reaction mechanism for the electrophilic addition of hydrogen bromide to 1-hexyne.
​

Question 10

Exhibit 9-2
To answer the following question(s),consider the information below:
​
The heat of hydrogenation of 1,4-pentadiene is 254.4 kJ/mol.The heat of hydrogenation of 1-pentyne is approximately 292.9 kJ/mol.
Refer to Exhibit 9-2.Which structure is more stable,1,4-pentadiene or 1-pentyne? Briefly explain your answer.

Question 11

Draw: ethynylcyclopropane

Question 12

Exhibit 9-3
Consider an unknown with the molecular formula C₄H₆.
Refer to Exhibit 9-3.How many degrees of unsaturation are present?

Question 13

Exhibit 9-1
The compound below has been isolated from the safflower plant.Consider its structure to answer the following question(s).
​
Refer to Exhibit 9-1.What is the molecular formula for this natural product?

Question 14

Exhibit 9-3
Consider an unknown with the molecular formula C₄H₆.
Refer to Exhibit 9-3.Draw six of the nine possible structures with this formula.

Question 15

Name:

Question 16

Exhibit 9-1
The compound below has been isolated from the safflower plant.Consider its structure to answer the following question(s).
​
Refer to Exhibit 9-1.Provide the name for this unusual natural product.

Question 17

Name:

Question 18

Draw the structure(s) of the product(s) formed when the following substance is treated with NaNH₂/NH₃ and 1-bromo-3-methylhexane.

Question 19

Draw: acetylene

Question 20

Draw the skeletal formula for the reactant and product that correspond to the enol formed in a hydroboration/oxidation reaction.Atoms other than carbon and hydrogen are labeled.

Question 21

Consider the following compound. This compound

A)is weakly acidic.
B)could produce a single carboxylic acid upon oxidation.
C)would produce a high yield of product upon oxidative cleavage.
D)yields an alkene upon treatment with hydrogen in the presence of a Lindlar catalyst.
E)None of the above characterize this compound

Question 22

​Draw the mechanism of the lithium/ammonia reduction of 2-butyne to produce trans-2-butene.

Question 23

The term retrosynthesis refers to syntheses developed:

A)starting with simple molecules.
B)devised by examining the product.
C)working forward and backward from intermediates.
D)beginning by examining the reactant available.

Question 24

What is the term given to the following species?

A)carbene
B)carbanion
C)acetylide anion
D)carbocation

Question 25

What is the skeletal formula for the product of the reaction when the following is treated with BH₃ in THF followed by H₂O₂?

A)
B)
C)
D)

Question 26

When the following substance is treated with 1 equivalent of Br₂, The product of the reaction is

A)
B)
C)
D)A mixture of a and b would be produced.

Question 27

An acetylide anion is more stable than either a vinylic or alkyl anion due to

A)the stabilization of the negative charge in orbitals with higher s character.
B)the greater distance of the negative charge from the nucleus of the carbon atom.
C)the greater stability of an sp hybrid orbital.
D)the larger number of π electrons.

Question 28

Draw the mechanism of the alkylation of acetylide anion with chloroethane to give 1-butyne.​

Question 29

When the following substance is treated with excess HBr, The product of the reaction is

A)
B)
C)
D)A mixture of a and b would be produced.
E)A mixture of a,b,and c would be produced.

Question 30

​Draw the mechanism of the bromination of acetylene.

Question 31

Which of the following alkynes will produce a single product upon mercury(II)-catalyzed hydration?

A)2-methyl-5-ethyl-3-heptyne
B)3,3-dimethyl-1-heptyne
C)3-hexyne
D)2-hexyne
E)Both 3,3-dimethyl-1-heptyne and 3-hexyne