Organic Chemistry : Help with Diels-Alder Reactions

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #1 : Specific Reactions And Named Reactions

When the following reaction is carried out, what kind of product is formed:

                                          Q12

Note: When an organic reaction employs heat, it is often shown as a delta over the reaction arrow.

Possible Answers:

A tricyclic system with two five-membered rings and a six-membered ring

A tricyclic system with a four-membered ring, a five-membered ring, and a six-membered ring

A bicyclic system with two six-membered rings

A tricyclic system with a five-membered ring and two six-membered rings

A bicyclic system with a five-membered ring and a six-membered ring

Correct answer:

A tricyclic system with a five-membered ring and two six-membered rings

Explanation:

This is a Diels-Alder reaction; these reactions happen between a nucleophilic diene, shown in blue below, and an electrophilic dienophile, in green. Diels-Alder reactions install a set of bonds that connect each external carbon of the diene system to an alkene carbon in the dienophile system to create a new six-membered ring. All remaining structure of the two reactants are retained, including the six- and five-membered rings below. The red bonds are the newly installed bonds.

                      A12

Example Question #2 : Specific Reactions And Named Reactions

What is the product of the reaction between 1,3-dibutene and bromoethene?

Possible Answers:

4-bromocyclohexene

No reaction occurs

3-bromocyclopentene

3-bromocyclohexene

None of these

Correct answer:

4-bromocyclohexene

Explanation:

The electrons from one of the double bonds on the 1,3-dibutene create a new single bond. The other new single bond is created from the electrons in the double bond of the other reactant. These two new single bonds join the reactants to create a cyclic product.

The electrons from the other double bond in the 1,3-dibutene move between the carbon 2 and 3. Thus, the final product is a 6-carbon cycloalkene with a halogen substituent.

Example Question #3 : Specific Reactions And Named Reactions

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What reagent(s) is/are needed to drive the given reaction?

Possible Answers:

Correct answer:

Explanation:

This is a standard Diels-Alder reaction. Diels-Alder reactions are driven solely by adding heat to the reagents. By looking at the reagents and the product, we can tell that this is a Diels-Alder reaction. For Diels-Alder, we need a cis-diene and an alkene as reactants. When these reactants are stimulated by heat, they form a cyclohexene product.

Example Question #4 : Specific Reactions And Named Reactions

Noname01

What is the product of the given reaction?

Possible Answers:

Noname05

Noname03

Noname02

Noname06

Noname04

Correct answer:

Noname02

Explanation:

This is a classic Diels-Alder reaction and it consists of a diene (cyclopentadiene) and a dienophile (ethene). The bicyclic structure forms if the electrons are moved in a circular fashion.

Example Question #1 : Help With Diels Alder Reactions

What is the product of the given reaction?Screen shot 2015 09 21 at 12.54.15 pm

Screen shot 2015 09 21 at 12.59.41 pm

Possible Answers:

I

III

IV

V

II

Correct answer:

II

Explanation:

Diels-Alder reactions create cyclohexene rings (eliminate III, IV, and V), and starting dienophile is trans (E conformation), so product is E (Eliminate I).

Example Question #6 : Specific Reactions And Named Reactions

What reaction forms a substituted cyclohexene system?

Possible Answers:

Wittig reaction

Diels-Alder reaction

Gabriel synthesis

Hoffmann elimination

Correct answer:

Diels-Alder reaction

Explanation:

The Diels-Alder reaction converts a conjugated diene and a substituted alkene into a six-membered ring containing cyclohexene (a substituted cyclohexene system). In Hoffmann elimination, tetra-alkyl ammonium salts undergo elimination to form the least substituted alkene. The Wittig reaction uses phosphorus ylides, aldehydes, or ketones to form an alkene and a triphenylphosphine oxide. Lastly, Gabriel synthesis forms primary amines via the reaction of a phthalimide with an alkyl halide, followed by cleavage with hydrazine.

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