Destroyer Orgo #76

[dentrilla]

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anyone care to explain? not sure about the explanation

 

[Orgolover]

dude/chick; you gotta post the question, or description of it; there are different editions...

 

[americanpierg]

anyone care to explain? not sure about the explanation

and H2O molecule is taken out and an ester is formed. simple.

 

[dentrilla]

oops ya.. its from 2009 ed. has nothing to do with forming an ether..

the question is about using HCl on a conjugated diene at -40degree's C.. I just havent come across these reactions and I'm wondering if there are any rules i should be aware of. It looks like something else happens if it happens round +50degrees?!

 

[wantVCUdental]

The answer is explained in the back...
the point here is that if it's under low temperature, then the most stable carbocation forms and there's no resonance, so the carbocation forms on the tertiary carbon.
hope that helps

 

[dentrilla]

Yah I know it is but I didnt wanna just memorize the reaction.. does this only work with conjugated diene's or can it be done if you have a conjugated triene?

And just to confirm the molecule doesnt have to be cyclic correct? And we name the carbon that gains the H, C-1?

Also, if anyone knows why heating something can cause a secondary carbocation to be more stable than a tertiary it would be nice to know 🙂

THanks!

 

[wantVCUdental]

heating inputs kinetic energy in to the molecule, so you get all kinds of stuff that wouldn't happen under normal conditions (i.e. the formation of a 2ndary carbocation even though the tertiary is more stable)

 

[americanpierg]

I don't have destroyer with me right now but I think i kind of remember this question. Review reactions with conjugated dienes

when two double bonds are one carbon apart, the reaction can lead to 1,2 addtion or 1,4 addition, depending on whether its through kenetic or thermodynamic control.

if its at low temperatures, it occurs through kenetic control, if it occurs at high temperatures, its through thermodynamic control.

kenetic control is 1,2 adition because that occurs the fastest and the carbocation intermediate is more stable, thermodynamic control is 1,4 addition because the product is more stable. H and Cl adds to the outside two carbons, and then the two double bonds disappear and a single double bond appears inbetween. its more stabalized than 1,2 addition. in conjugated dienes

 

[americanpierg]

Also, if anyone knows why heating something can cause a secondary carbocation to be more stable than a tertiary it would be nice to know 🙂

THanks!

Heating won't cause a secondary carbocation to be more stable than a tertiary carbocation. The 1,4 product is more stable than the 1,2 product, but the 1,2 intermediate is more stable than the 1,4 intermediate.

At low temperatures, the fastest reaction, not the most stable, will be the major product. The fastest would be the 1,2 addition. because the tertiary carbocation is more stable.

 

[ugination87]

Around -80C is the kinetic reaction. This is when the a double bond attacks HCl and the H goes on C1. This leaves a carbocation on C2, which the Cl:- attacks.

The other reaction your talking about is the 1,4 reaction. This takes place in warmer temp around 40C. The double bond attacks HCl and H goes on C1. Then, through resonance, the carbocation is on C4, which the Cl:- attacks. Thus, the 1,4 reaction. This is a thermodynamic reaction.

 

[dentrilla]

Got it, thanks guys.

Now what about a triene.. lol... whenever destroyer explains this type of question it always makes a point to say diene, I'm guessing thats the only way these reactions work. Someone correct me if I'm wrong.

Thnx again