Diels-Alder Reaction: A Simple Explanation?

In summary, the professor's explanation of Diels-Alder reactions focused on electrostatics rather than molecular orbitals. However, this approach raises questions about the stability of ethene and the explanation of stereoselectivity. The conversation also suggests that the professor did not discuss orbital symmetries.
  • #1
Qube
Gold Member
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Homework Statement



This is my prof's explanation of Diels-Alder ... below is the mechanism and some resonance structures he drew to explain the concerted movement of electrons to the class ...

5dYQD.jpg


Homework Equations



Nucleophiles attack electrophiles.

Electrons in HOMOs go into LUMOs.

The Attempt at a Solution


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So my professor's explanation is very interesting for a few reasons:

1) He completely sidesteps all the ramblings about molecular orbitals in the text.

2) His electrostatic explanation is very tempting based on Occam's razor alone but ethene is a gas at STP. If the dipolar resonance structure were a big contributor then wouldn't ethene instead be a liquid?

3) The book has a section on stereoselectivity and Diels-Alder reactions. How can pure electrostatics explain stereoselectivity?

So am I crazy or what for thinking that the guy's electrostatic explanation sounds like a story of unicorns in the park?
 
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  • #2
Qube said:
unicorns in the park?
Are you certain he wasn't discussing "orbital symmetries" with his plus and minus signs?
 
  • #3
Bystander said:
Are you certain he wasn't discussing "orbital symmetries" with his plus and minus signs?

Yes I'm sure he didn't mention orbitals at all.
 

What is the Diels-Alder reaction?

The Diels-Alder reaction is a chemical reaction that involves the formation of a new carbon-carbon bond between a conjugated diene and a dienophile. It is a cycloaddition reaction that is often used in organic synthesis to create six-membered rings.

What is a conjugated diene?

A conjugated diene is a molecule that contains two double bonds that are separated by one or more single bonds. These double bonds are in a specific arrangement, known as a conjugated system, which allows for the formation of new bonds through the Diels-Alder reaction.

What is a dienophile?

A dienophile is a molecule that reacts with a conjugated diene in a Diels-Alder reaction. It typically contains a double bond, or a functional group that can form a double bond, and is electron-deficient, making it highly reactive towards the electron-rich conjugated diene.

What are the driving forces of a Diels-Alder reaction?

The driving forces of a Diels-Alder reaction are the formation of a new carbon-carbon bond and the formation of a more stable product. This reaction is also thermally favorable, as the newly formed six-membered ring is more stable than the starting materials.

What is the mechanism of a Diels-Alder reaction?

The mechanism of a Diels-Alder reaction involves a concerted cycloaddition of the conjugated diene and the dienophile. The reaction proceeds through a transition state in which the diene and dienophile overlap to form a new six-membered ring. This transition state then collapses to form the final product.

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