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Author Topic: Why there is no 'quadra' bond?  (Read 12252 times)

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lsc04361

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Why there is no 'quadra' bond?
« on: November 14, 2009, 11:09:28 PM »

There is single, double and triple bond.
but how about quadra bond?
why there is no quadra bond?

p.s. certainly there is a lot of element forming compound and obtain more than 8 electrons in outermost shell
e.g. XeF4, SF6 .etc
so the octet structure isn't a explanation for not having quadra bond.

does it relates to the placement of the unhybridized orbitals?

thx
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cth

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Re: Why there is no 'quadra' bond?
« Reply #1 on: November 15, 2009, 12:36:07 AM »

You're right when you say there exists no quadruple bond for most compounds, and particularly organic ones. But, there are a few exceptions, as some transition metals do form quadruple bonds, like molybdenum and rhenium http://en.wikipedia.org/wiki/Quadruple_bond.

Even more!  :) Quintuple bonds have been reported, again between some transition metals http://en.wikipedia.org/wiki/Quintuple_bond.


But, why doesn't carbon form quadruple bonds? That would imply that all the atomic orbitals 2s and 2p from C are involved in the bonding interaction. First with the 2p orbitals, you form one sigma bond  and two pi bonds. And now, due to the geometry of the remaining 2s orbital, it can only form sigma bond as well. But, you can't have two sigma bonds to form one quadruple bond, because both are lying in the axis (as opposed to pi bonds that are on the side). The two sigma bounds would get into one another and interact too strongly for the compound to be stable.

Quadruple and quintuple bonds are possible with transition metals due to their 3d orbitals, which give more space for more interactions.
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Ranadeep

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Re: Why there is no 'quadra' bond?
« Reply #2 on: November 15, 2009, 03:23:19 AM »

Nice info bro cth ..never knew that quadraple bonds exist ! ..
Last year when i was taught about Hybridization concept i got a similar doubt and and i formed a Never existing compound called C2 !
                         
                         
C=+= C .. lol i want 4 lines there hehe

ie; the 2 carbons atoms with SP2 hybridization .

i mean there will be a P-P Sigma Bond and 3 SP2-SP2 pi Bonds !
i think its complicated lol but its just one of creative ideas ive got but i think its highly unstable due to formation of only 1 sigma and 3pi bonds : )


   
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I am 15 from India and i like doing chemistry

cth

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Re: Why there is no 'quadra' bond?
« Reply #3 on: November 15, 2009, 05:19:58 AM »

You're welcome. Nice imagination  ;)

For the hypothetical C2 molecule with a quadruple bond, you would need either:
* σ4π4. Impossible because the two σ bonds would get into one another.
* σ2π6. Impossible because there can be only two π bonds from the 2p orbitals.
* σ2π4δ2. In theory possible to put electrons into the carbon 3d orbitals, but no way it is going to be stable. 3d orbitals are too high in energy compared to 2s and 2p.

Carbon chemistry is already rich enough. No need of quadruple bonds to make it even more complicated!  ;D
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lsc04361

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Re: Why there is no 'quadra' bond?
« Reply #4 on: November 15, 2009, 10:51:09 PM »

really thx to cth.
i never know there is quadruple bond.
thank you very much.
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