[orgo] allyl stability

[ippie]

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question is attached.

#1. which is the right decreasing order of allyl stability?
=> answer is B, but I think the answer is E.
the stability of allyl is... substituted ally > tertiary > allyl > secondary > primary > vinyl.
right? do you guys agree that?

#2. two isomers of the same molecular formula are closest in physical and chemical properties when jointly exhibiting
a. conformational isomer
b. enantiomeric isomer
=> the answer is a. why not b? because enantiomers have the same (not closest) physical and chemical properties?

#3. the explanation of the question #2 was as follows...
"isomers of the same molecular fomula can be arranged with increasing order of differences in physical and chemical properties outlined as follows...
conformational isomers > enantiomers > diastereomers and geometric isomers > constitutional isomers"
do you agree this? I think enantiomers have exactly the same physical and chemical properties, but conformational isomers have a slightly different physical and chemical properties.

 

[userah]

conformational are the closest alike because they only move about around one bond. Conformational is where you have the anti, gauche,eclipsed forms. If you have a kaplan book,take a look at...i think it's chapter 2. it goes through all the isomers and their properties

 

[doc3232]

So resonance is the most important thing in ochem.
So when you have conjugation then it 99.99% of the time the most stable structure.
The double bond in the allylic position makes the radical much more stable.
Take 1 electron from then double bond and make a new bond with the radical on the left.
That would make a new double bond 1 carbon left of the original and the radical would now be on the left side.
Answer: Resonance always dominates.

 

[userah]

a tertiary allylic radical would be the mooost stable of all

 

[doc3232]

a tertiary allylic radical would be the mooost stable of all

Unless there is resonance. Resonance from a double bond would have a much more substantial effect on stability.

 

[userah]

an allylic radical is stabilized by resonance...

 

[doc3232]

an allylic radical is stabilized by resonance...

woooops, sorry.

 

[Hugh Mannity]

Conformation also includes like boat and chair cyclohexane. Even if the molecule is in boat/chair, it is still named the same and is essentially the same molecule because it is not connected differently, just rotated bonds.

 

[ippie]

tertiary allyl is the most stable, but primary allyl is less stable than tertiary carbocation. It's from McMurry Orgo book. Does anybody agree?

 

[Ghettob1aster]

The book said a tertiary is more stable than an allylic?

I would think resonance would be more dominating than inductive effects or hyperconjugation if you just think about it, right?

 

[doc3232]

The book said a tertiary is more stable than an allylic?

I would think resonance would be more dominating than inductive effects or hyperconjugation if you just think about it, right?

Ya, your right.