Deck 4: Introduction to Alkenes and Alkynes

Question 1

Complete the reaction by giving the products. Show all unshared electron pairs and formal charges.

Answer 1

Question 2

Consider this reaction. Draw a curved-arrow mechanism for the reaction. Notice that concentrated acid is present as a catalyst. (You can abbreviate the catalyst as H-A in your mechanism.) This mechanism should be a series of acid-base steps.

Answer 2

The curved-arrow mechanism is as follows. This is by analogy to the mechanism of HBr addition or the mechanism of hydration, both of which go through a carbocation intermediate.
As noted in the problem, you could use H₂SO₄ as your acid or abbreviate it with H-A. If you ionized the methanol and let the conjugate base attack the carbocation, this is not the expected pathway.

Question 3

Consider this reaction. Which reaction would be faster: this reaction or the reaction of propene (H₂C=CHCH₃) with methanol to give isopropyl methyl ether (CH₃)₂CH-OCH₃? Explain. Hammond's postulate should be part of your explanation.

Answer 3

We let the relative energies of the carbocation intermediates guide us and invoke Hammond's postulate, which says that the energies of the transition states should be approximated by the energies of the carbocation intermediates. Hence, the reaction with the more stable carbocation intermediate should be the faster reaction. Because addition to propene involves a secondary carbocation, whereas the reaction above involves a more stable tertiary carbocation, the reaction above is a lot faster.
You must specifically mention the connection between transition states and reactive intermediates (for example, carbocations) for full credit.

Question 4

Name the following compound and include the E or Z designation in the name.

Question 5

An alcohol has an empirical formula of C₁₂H₂₀O and a molecular mass of about 360. How many rings plus double bonds does it contain? (Atomic masses: C = 12, H = 1, O = 16)

Question 6

Give the structure of the HBr addition product.

Question 7

Name the compound. Include an E or Z designation if appropriate.

Question 8

Consider this molecule:
Which bond is an sp²-sp³  bond?

A) bond (a)
B) bond (b)
C) bond (c)
D) bond (d)
E) bond (e)

Question 9

Provide an IUPAC name for the compound.

Question 10

Consider the reaction free-energy diagram for two reactions that convert reactants (R) into products (P) and select the two correct statements.

A) Reaction 1 is faster because it occurs in one step.
B) Reaction 2 is faster than reaction 1.
C) Both reactions occur at the same rate at a given concentration of R.
D) X is a transition state of reaction 2.
E) The rate-limiting step of reaction 2 is R ⇌ X.f.
The rate-limiting step of reaction 2 is X ⇌ P.g.
X must be a carbocation.

Question 11

Give the IUPAC name, including stereochemistry, of the compound:

Question 12

Give the structure of the carbocation intermediate and the curved-arrow notation for its formation in the addition reaction of 2-methyl-1-hexene with HBr.

Question 13

Name this compound (including stereochemical configuration where appropriate).

Question 14

14. In each pair, identify the more stable one (as measured by heats of formation).
-1:
The more stable compound is ________________.

A) Compound a
B) Compound b

Question 15

14. In each pair, identify the more stable one (as measured by heats of formation).
-2:
The more stable compound is ________________.

A) Compound a
B) Compound b

Question 16

In this pair of compounds, identify the more stable one (as measured by heats of formation).

A) Compound a
B) Compound b

Question 17

Which of these alkenes has the smallest (or more negative) heat of formation?

A) Compound A
B) Compound B
C) Compound C
D) Compound D
E) Compound E

Question 18

Complete the reaction by giving the major organic product(s).

Question 19

Complete the reaction by giving the major organic product(s).

Question 20

Complete the reactions by giving the major organic product.

Question 21

Select the true statements that apply to a hydrocarbon, compound X, with the molecular formula C₁₀H₁₄. For purposes of the first two statements, a benzene ring has this skeletal structure:

A) Compound X could contain a benzene ring.
B) Compound X must contain a benzene ring.
C) Compound X has an unsaturation number of 8.
D) Compound X has an unsaturation number of 4.
E) Compound X could contain three double bonds and one triple bond.

Question 22

Complete the reaction by giving the structure of the organic product.

Question 23

Provide an IUPAC name for the following compound.

Question 24

A multistep reaction A ⇌ B ⇌ C ⇌ D has the free energy-reaction coordinate diagram shown below. Which step of the reaction is rate-limiting in the forward direction?

A) the reaction of A to B
B) the reaction of B to C
C) the reaction of C to D

Question 25

This carbocation undergoes rearrangement. Give the structure of the rearranged carbocation and, on the structure given, the curved-arrow notation for the rearrangement.

Question 26

Identify the most stable carbocation:

A) carbocation A
B) carbocation B
C) carbocation C