Cyclooctatetraene hybridzation

[SaintJude]

1 .What's hybridization of carbons in Cycloblahah?

2. And can I assume that any compound with 8 or more atoms is non-planar due to its attempt to alleviate bond strain?

edit....Darn it no. The compound on the right w/ methyl groups IS planar....

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[SaintJude]

Hmm, browsed around:

the number of π electrons in the system is crucial: when they have 4 or 8 π electrons both cyclooctatetraene and benzene adopt non-planar geometries; when they have 6 or 10 π electrons a conjugated planar geometry is preferred.

So the right-hand compound has 10pi electrons and is therefore planar? Do we need to know this 4/8 vs. 6/10 rule?

 

[chiddler]

1 .What's hybridization of carbons in Cycloblahah?

2. And can I assume that any compound with 8 or more atoms is non-planar due to its attempt to alleviate bond strain?

edit....Darn it no. The compound on the right w/ methyl groups IS planar....

no regardless of how stable or unstable it is, SP2's are planar! therefore this molecule is planar.

I think we do need to know huckel's rule. if not, know it anyway just in case because it's so easy to remember. but that doesn't really answer the question anyway.

 

[Jarudy]

1. sp2
2. No. Substituents can force certain conformations and prevent conformational changes.

1 .What's hybridization of carbons in Cycloblahah?

2. And can I assume that any compound with 8 or more atoms is non-planar due to its attempt to alleviate bond strain?

edit....Darn it no. The compound on the right w/ methyl groups IS planar....

 

[SaintJude]

Just to clarify, cyclooctatetraene Is non-planar (Kaplan & Wiki) although its carbons are sp2 hybridized.

So the previous replies are confusing me.

 

[chiddler]

Just to clarify, cyclooctatetraene Is non-planar (Kaplan & Wiki) although its carbons are sp2 hybridized.

So the previous replies are confusing me.

no idea, would love an explanation why the molecule is not planar, please!

 

[syoung]

http://forums.studentdoctor.net/showthread.php?t=643195

 

[SaintJude]

Yeah, so I saw this thread...but they didn't really come to a conclusion. To be honest, it looks like they all kind of gave up.

I mean, maybe it's just something I'll remember: 4/6 pi electrons are planar (like benzene) but 8/10 pi electron compound are not.

 

[shamwowzer]

Yeah, so I saw this thread...but they didn't really come to a conclusion. To be honest, it looks like they all kind of gave up.

I mean, maybe it's just something I'll remember: 4/6 pi electrons are planar (like benzene) but 8/10 pi electron compound are not.

Just because something is sp2 does not make it planar. Two sp2 molecules can be connected but oriented in space differently leading to a non planar molecule.

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[SaintJude]

Just because something is sp2 does not make it planar. Two sp2 molecules can be connected but oriented in space differently leading to a non planar molecule.

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👍

 

[chiddler]

Just because something is sp2 does not make it planar. Two sp2 molecules can be connected but oriented in space differently leading to a non planar molecule.

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i did not know that. why/how?

and can i please have some examples?

 

[syoung]

i think it depends if the planar form will cause it to be "unstable" if so, then it will adopt chair or tub formation, like the cyclooctblahblah
but like benzene, it is SUPER stable flat, so there it lies. flat. but both have sp2 carbons.

 

[chiddler]

i think it depends if the planar form will cause it to be "unstable" if so, then it will adopt chair or tub formation, like the cyclooctblahblah
but like benzene, it is SUPER stable flat, so there it lies. flat. but both have sp2 carbons.

But I don't understand how it works given the geometry.

can you imagine making anything other than a planar structure out of these? besides lining them up like a plus sign, anyway.

 

[syoung]

think I meant the ones that are conjugated and in a ring form. of some sort.

 

[milski]

There can be some rotation around the double bond between the two carbons. The π orbitals do not align perfectly but it's still more stable than the planar version which would have increased angles between the C-C bonds.

The planar form is supposedly less stable (due to the bond angle strain?) and the lack of stabilizing conjugation.

"Experimental studies and theoretical calculations indicate that the structure of cyclooctatetraene showing in figure 11.12 is about 75kJ/mol more stable than the planar delocalized alternative." (Carey, Guiliano, 8E)

 

[Doktor Sahar]

Well, first off, cyclooctatetraene is actually non-planar and we know that its hybridization is sp2. This is a bit controversial though.

A friend of mine did his thesis on cyclooctatetraene, and I'm pretty sure what that guy said about it being sp, is totally wrong.

And, honestly, I never imagined cyclooct... being on the MCAT...are you serious?! 😱


Shamwowzer......most of the time that actually IS the case. Get at me if you need proof.

 

[pm1]

1 .What's hybridization of carbons in Cycloblahah?

2. And can I assume that any compound with 8 or more atoms is non-planar due to its attempt to alleviate bond strain?

edit....Darn it no. The compound on the right w/ methyl groups IS planar....

I thought it is not planar because it does not meet Huckel's law, hence it is not a, aromatic compound, nor planar.
4 or 8 electrons do not fulfill the rule that in order to be aromatic the compound must have 4npi+2 electrons, while 6 and 10 do.