How do we decide that cyclic structures are planar or not?
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When you look at the structure of a six-membered ring, if all the molecular geometriesaround each atom in the ring are sp2-hybridized, then the whole molecule is planar.
It's not always the case for rings of other sizes, but for six-membered rings, it usually is true.
...But if all bonds have 100% restricted rotationAND are restricted to be in one plane, then it's even more likely that it IS planar (even if one atom appears to not be sp2-hybridized...). Pyrrole, furan, and thiophene are interesting five-membered ring examples of this.
With five-membered rings, having one heteroatom in addition to four sp2-hybridized atoms helps, especially if that heteroatom has a smaller valency than carbon, but it doesn't guarantee anything.
It's not always the case for rings of other sizes, but for six-membered rings, it usually is true.
...But if all bonds have 100% restricted rotationAND are restricted to be in one plane, then it's even more likely that it IS planar (even if one atom appears to not be sp2-hybridized...). Pyrrole, furan, and thiophene are interesting five-membered ring examples of this.
With five-membered rings, having one heteroatom in addition to four sp2-hybridized atoms helps, especially if that heteroatom has a smaller valency than carbon, but it doesn't guarantee anything.
Answered by
1
When you look at the structure of a six-membered ring, if all the molecular geometriesaround each atom in the ring are sp2-hybridized, then the whole molecule is planar.
It's not always the case for rings of other sizes, but for six-membered rings, it usually is true.
...But if all bonds have 100% restricted rotationAND are restricted to be in one plane, then it's even more likely that it IS planar (even if one atom appears to not be sp2-hybridized...). Pyrrole, furan, and thiophene are interesting five-membered ring examples of this.
With five-membered rings, having one heteroatom in addition to four sp2-hybridized atoms helps, especially if that heteroatom has a smaller valency than carbon, but it doesn't guarantee anything.
Here are a few examples of planar and non-planar six-membered rings.
cyclohexane, cyclohexene, 1,3-cyclohexadiene, and benzene
Notice how the ring gets more planar with an increasing number of sp2 carbons. That usually is how it goes, but not always.
For five-membered rings, it's harder to find examples, but here are some examples that may contain heteroatoms:
pyrrole, imidazole, furan, and 1,3-cyclopentadiene
For rings with more than six members, it becomes less likely that all sp2-hybridized ring atoms is the only requirement for planarity. Here's an example of a non-planar molecule with all seemingly-sp2-hybridized carbons in its flat structure:
1,3,5,7-cyclooctatetraene
Its actual structure is:
So how would you actually know for sure? Do some X-ray crystallography or X-ray diffraction and determine the structure
It's not always the case for rings of other sizes, but for six-membered rings, it usually is true.
...But if all bonds have 100% restricted rotationAND are restricted to be in one plane, then it's even more likely that it IS planar (even if one atom appears to not be sp2-hybridized...). Pyrrole, furan, and thiophene are interesting five-membered ring examples of this.
With five-membered rings, having one heteroatom in addition to four sp2-hybridized atoms helps, especially if that heteroatom has a smaller valency than carbon, but it doesn't guarantee anything.
Here are a few examples of planar and non-planar six-membered rings.
cyclohexane, cyclohexene, 1,3-cyclohexadiene, and benzene
Notice how the ring gets more planar with an increasing number of sp2 carbons. That usually is how it goes, but not always.
For five-membered rings, it's harder to find examples, but here are some examples that may contain heteroatoms:
pyrrole, imidazole, furan, and 1,3-cyclopentadiene
For rings with more than six members, it becomes less likely that all sp2-hybridized ring atoms is the only requirement for planarity. Here's an example of a non-planar molecule with all seemingly-sp2-hybridized carbons in its flat structure:
1,3,5,7-cyclooctatetraene
Its actual structure is:
So how would you actually know for sure? Do some X-ray crystallography or X-ray diffraction and determine the structure
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