Organic Question (TopScore)

[Darknight260]

Advertisement - Members don't see this ad

[answer: E]

Ok, so I know that the carbocation could go under rearrangement in the Markovnikov addition, but why on earth would go from a secondary carbocation to a primary??? Was this question just simply asking for all of the "possible" products? Because to my understanding the amount of product C produced would be negligible to none, right?

 

[needzmoar]

This reaction is under kinetic/thermo control. Although they didn't specify the temperature, at higher temperatures, the more stable product dominates (choice C) because the di-substituted alkene has more hyper-conjugation.

 

[FROGGBUSTER]

An allylic carbocation forms, and it's very stable.

For conjugated dienes, the 1,2-addition product preferentially forms at low temperatures (kinetic product) while the 1,4-addition thermo product preferentially form at high temps.

http://www.cliffsnotes.com/study_gu...ons.topicArticleId-22667,articleId-22655.html

 

[Darknight260]

Ahhh okay, I was completely overlooking the fact that the carbocation was resonance stabilized (dur!). But I did not know about that thermodynamic control. Thanks for clearing that up!

 

[Barking Lamb]

Try to remember that Butadiene goes into allylic resonance.

C=C--C=C is the structure. The hydrogen will add to the least substituted as you predicted in order to avoid a primary carbo-cation.

[ H-C--C(+)--C=C] Is the form you predicted!

BUT... It has a resonance form. [H-C--C=C--C(+)]