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Conformation of six-membered ring constituting a bridged compound
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Ng?c Anh Thái
Conformation of six-membered ring constituting a bridged compound
Norbornane, as mentioned by the other answers forces the cyclohexane ring into a prototypical "boat" conformation. The bridging carbon creates two five-membered rings in the low-energy envelope or "pucker" conformation:
Put simply, the 1-carbon bridging system creates a very rigid system. While there are many eclipsed C-H interactions, changing conformation would require stretching bonds or angles - distortions that are much higher in energy.
In larger bicycloalkanes, like bicyclo[2.2.2]octane, there is now more conformational flexibility to adopt a twist-boat conformation:
Notice that from the bridgehead carbons, there are many eclipsing interactions. In Avogadro, I can watch this all-boat conformation twist into the twist-boat:
While it's important to do conformational analysis for every molecule (small interactions can change the low-energy conformer), I would guess most of the larger bicycloalkanes to adopt twist-boat configurations.
Norbornane, as mentioned by the other answers forces the cyclohexane ring into a prototypical "boat" conformation. The bridging carbon creates two five-membered rings in the low-energy envelope or "pucker" conformation:
Put simply, the 1-carbon bridging system creates a very rigid system. While there are many eclipsed C-H interactions, changing conformation would require stretching bonds or angles - distortions that are much higher in energy.
In larger bicycloalkanes, like bicyclo[2.2.2]octane, there is now more conformational flexibility to adopt a twist-boat conformation:
Notice that from the bridgehead carbons, there are many eclipsing interactions. In Avogadro, I can watch this all-boat conformation twist into the twist-boat:
While it's important to do conformational analysis for every molecule (small interactions can change the low-energy conformer), I would guess most of the larger bicycloalkanes to adopt twist-boat configurations.
Relative energy of hydrocarbon conformers is reasonably tricky question, involving among others long range weak interactions, dynamic effects and symmetry. Thats why I (as computational chemist) tried to avoid answer based on calculations. BTW, how large is the energy difference of those?More
Norbornane and its derivatives are often used for studying effect of equatorial and axial substitution of cyclohexane and is considered rigid.
Therefore, I don't expect significant population of the second conformer you sketched.
Edit:
For the [2.2.2]bicyclooctane (not the lactone mentioned in question), both conformers are known in crystalographic database.
Bear in mind, that bicyclooctane constist of three hypothetical cyclohexanes, possibly equivalent by symmetry.
For any compound of interest, you should find enough data in crystallographic database, but I'd expect all reasonable conformations to exist.
Norbornane and its derivatives are often used for studying effect of equatorial and axial substitution of cyclohexane and is considered rigid. Therefore, I don't expect significant population of the second conformer you sketched.
Edit:For the [2.2.2]bicyclooctane (not the lactone mentioned in question), both conformers are known in crystalographic database.
Bear in mind, that bicyclooctane constist of three hypothetical cyclohexanes, possibly equivalent by symmetry.
For any compound of interest, you should find enough data in crystallographic database, but I'd expect all reasonable conformations to exist.
I need for one of these answers so I can accept it. Geoff said that the most stable conformation for bicyclo[2.2.2]octane is twist-boat, XuMuk said that it is boat and you didnt give a definite answer on that matter.More
Norbornane, as mentioned by the other answers forces the cyclohexane ring into a prototypical "boat" conformation. The bridging carbon creates two five-membered rings in the low-energy envelope or "pucker" conformation:
Put simply, the 1-carbon bridging system creates a very rigid system. While there are many eclipsed C-H interactions, changing conformation would require stretching bonds or angles - distortions that are much higher in energy.
In larger bicycloalkanes, like bicyclo[2.2.2]octane, there is now more conformational flexibility to adopt a twist-boat conformation:
Notice that from the bridgehead carbons, there are many eclipsing interactions. In Avogadro, I can watch this all-boat conformation twist into the twist-boat:
While it's important to do conformational analysis for every molecule (small interactions can change the low-energy conformer), I would guess most of the larger bicycloalkanes to adopt twist-boat configurations.
Norbornane, as mentioned by the other answers forces the cyclohexane ring into a prototypical "boat" conformation. The bridging carbon creates two five-membered rings in the low-energy envelope or "pucker" conformation:
Put simply, the 1-carbon bridging system creates a very rigid system. While there are many eclipsed C-H interactions, changing conformation would require stretching bonds or angles - distortions that are much higher in energy.
In larger bicycloalkanes, like bicyclo[2.2.2]octane, there is now more conformational flexibility to adopt a twist-boat conformation:
Notice that from the bridgehead carbons, there are many eclipsing interactions. In Avogadro, I can watch this all-boat conformation twist into the twist-boat:
While it's important to do conformational analysis for every molecule (small interactions can change the low-energy conformer), I would guess most of the larger bicycloalkanes to adopt twist-boat configurations.
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According to structure determined by electron diffraction, norbornane is present in bridged boat conformation. http://pubs.acs.org/doi/abs/10.1021/ja01014a032, see Figure.
Norbornane and its derivatives are often used for studying effect of equatorial and axial substitution of cyclohexane and is considered rigid. Therefore, I don't expect significant population of the second conformer you sketched.
Edit: For the [2.2.2]bicyclooctane (not the lactone mentioned in question), both conformers are known in crystalographic database.
Bear in mind, that bicyclooctane constist of three hypothetical cyclohexanes, possibly equivalent by symmetry.
For any compound of interest, you should find enough data in crystallographic database, but I'd expect all reasonable conformations to exist.
According to structure determined by electron diffraction, norbornane is present in bridged boat conformation. http://pubs.acs.org/doi/abs/10.1021/ja01014a032, see Figure.
Norbornane and its derivatives are often used for studying effect of equatorial and axial substitution of cyclohexane and is considered rigid. Therefore, I don't expect significant population of the second conformer you sketched.
Edit:For the [2.2.2]bicyclooctane (not the lactone mentioned in question), both conformers are known in crystalographic database.
Bear in mind, that bicyclooctane constist of three hypothetical cyclohexanes, possibly equivalent by symmetry.
For any compound of interest, you should find enough data in crystallographic database, but I'd expect all reasonable conformations to exist.
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