Diels Alder Help!

[BiomajorPreDent]

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Okay, I might be a bit anal here..but on destroyer 76 (2009 ed) I just noticed that the molecule is locked in S-Trans form.

I have this exact structure in my ochem textbook and it says that this will not react when its locked in S-Trans..it only works if its S-Cis

But destroyer shows a 1,2 addition and makes no mention of its S-Trans form

Can someone shed some light on this? 😕

 

[UCB05]

I dont have the 2009 edition of destroyer. The point about the Diels-Alder reaction is that the diene has to be able to react in the cis conformation because the transition state and product is a cyclohexene ring. The cis/trans geometry of the dienophile does not inhibit the reaction though. That just determines the conformation of the substituents in the product.

I don't know where a 1,2 addition that you mention comes in. Are you talking about a different reaction mechanism, maybe?

 

[Shinpe]

Hmm I have the jan 2009 version. Are you talking about the one that says "predict the product at -40 for..."? This is not a Diels-alder reaction. This is just a electrophilic addition of HCl to a conjugated diene. Since it's at -40, it's gonna be under kinetic control and give 1,2-addition while at higher temperatures, it would give 1,4-addition under thermodynamic control.

 

[BiomajorPreDent]

I dont have the 2009 edition of destroyer. The point about the Diels-Alder reaction is that the diene has to be able to react in the cis conformation because the transition state and product is a cyclohexene ring. The cis/trans geometry of the dienophile does not inhibit the reaction though. That just determines the conformation of the substituents in the product.

I don't know where a 1,2 addition that you mention comes in. Are you talking about a different reaction mechanism, maybe?

Yes, I got this confused with the Diels-Alder

Hmm I have the jan 2009 version. Are you talking about the one that says "predict the product at -40 for..."? This is not a Diels-alder reaction. This is just a electrophilic addition of HCl to a conjugated diene. Since it's at -40, it's gonna be under kinetic control and give 1,2-addition while at higher temperatures, it would give 1,4-addition under thermodynamic control.

Holy crap! You are right I am so dumb..and I got this correct when I did it, but I was just browsing through really fast and was like wait a minute....s-trans?

Thanks!!

 

[Sublimation]

Just know that under kinetic control you want the intermediate with the lower activation energy the secondary carbocation, giving rise to the 1,2 addition. while on the other hand with thermodynamic control you will get the more subst. product and more stable produc the 1,4 addition.