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Topic: Cyanide as a Lewis Base  (Read 498 times)

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Offline Varlam

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Cyanide as a Lewis Base
« on: June 26, 2019, 01:07:13 AM »
From which orbital of cyanide (CN-) an electron pair is donated to a lewis acid?

Hybridization of carbon in cyanide is sp. The two pi bonds are formed by 2Px + 2Px, and 2Py + 2Py.

So is the donated electron pair from 2s orbital of nitrogen? or from sp orbital of carbon?

Offline Borek

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Re: Cyanide as a Lewis Base
« Reply #1 on: June 26, 2019, 03:03:47 AM »
So is the donated electron pair from 2s orbital of nitrogen? or from sp orbital of carbon?

I would say neither. Atomic orbitals (especially those from valence shells) combine creating molecular orbitals, so it doesn't make much sense to assign electrons to specific atoms.
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Offline Corribus

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Re: Cyanide as a Lewis Base
« Reply #2 on: June 26, 2019, 09:04:21 AM »
Totally. In the MO point of view, about the best you can say is that the valence electrons come from an orbital that has a majority fraction of carbon character, meaning the orbital contains more carbon atomic orbital character than nitrogen character.

https://chemistry.stackexchange.com/questions/18449/cyanide-ion-non-bonding-lone-pair
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Offline Babcock_Hall

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Re: Cyanide as a Lewis Base
« Reply #3 on: June 26, 2019, 10:15:22 AM »
Suppose one wished to use a model based on hybridized orbitals.  I would suppose that the unshared pair on the carbon atom are in its sp orbital.  Likewise the unshared pair on nitrogen is in its sp orbital, not an s orbital.

Offline Varlam

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Re: Cyanide as a Lewis Base
« Reply #4 on: June 26, 2019, 03:27:58 PM »
So is the donated electron pair from 2s orbital of nitrogen? or from sp orbital of carbon?

I would say neither. Atomic orbitals (especially those from valence shells) combine creating molecular orbitals, so it doesn't make much sense to assign electrons to specific atoms.

I think not all orbitals of valence shell combine in the case of cyanide. Nitrogen has a lone pair which does not involve in covalent bonding. Carbon has a pair of electrons too which don't get shared.

Offline Varlam

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Re: Cyanide as a Lewis Base
« Reply #5 on: June 26, 2019, 03:39:38 PM »
Suppose one wished to use a model based on hybridized orbitals.  I would suppose that the unshared pair on the carbon atom are in its sp orbital.  Likewise the unshared pair on nitrogen is in its sp orbital, not an s orbital.

The electronic configuration of nitrogen is:1s2 2s2 2p3
so I think the unshared pair is two electrons on 2s orbital. Correct me If I am mistaken.

Offline Borek

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Re: Cyanide as a Lewis Base
« Reply #6 on: June 26, 2019, 04:28:55 PM »
I think not all orbitals of valence shell combine in the case of cyanide. Nitrogen has a lone pair which does not involve in covalent bonding. Carbon has a pair of electrons too which don't get shared.

That's an oversimplification. All atomic orbitals take - to some extent - part when the molecule is created. For some (especially those from lower shells) the effect (change in the original electron density) is negligible, but all valence electrons are affected. In most cases we can approximate the final effect reasonably well treating orbitals the way you do, but that's only an approximation.
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Offline Varlam

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Re: Cyanide as a Lewis Base
« Reply #7 on: June 26, 2019, 04:35:50 PM »
I think not all orbitals of valence shell combine in the case of cyanide. Nitrogen has a lone pair which does not involve in covalent bonding. Carbon has a pair of electrons too which don't get shared.

That's an oversimplification. All atomic orbitals take - to some extent - part when the molecule is created. For some (especially those from lower shells) the effect (change in the original electron density) is negligible, but all valence electrons are affected. In most cases we can approximate the final effect reasonably well treating orbitals the way you do, but that's only an approximation.
The lewis structure of cyanide is as shown in the link below.In the diagram, there are two lone pairs, one for each atom. My question is: when reacting with a lewis acid, which lone pair is donated? the pair on carbon or nitrogen?
https://d2jmvrsizmvf4x.cloudfront.net/R1n78jFTigdpVxG2kcQU_picturecn.png

Offline Babcock_Hall

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Re: Cyanide as a Lewis Base
« Reply #8 on: June 26, 2019, 09:00:03 PM »
Suppose one wished to use a model based on hybridized orbitals.  I would suppose that the unshared pair on the carbon atom are in its sp orbital.  Likewise the unshared pair on nitrogen is in its sp orbital, not an s orbital.

The electronic configuration of nitrogen is:1s2 2s2 2p3
so I think the unshared pair is two electrons on 2s orbital. Correct me If I am mistaken.

The triple bond between carbon and nitrogen has two kinds of bonding.   One bond is formed from the overlap of one sp orbital on carbon with an sp orbital on nitrogen.  This bond has greatest electron density along the internuclear axis.  Each of the two other bonds results from side-by-side overlap of a p orbital on carbon with a p orbital on nitrogen.  That leaves one more sp orbital so far unaccounted for on each atom.  One sp orbital is where the lone pair on nitrogen is, and one sp orbital is for carbon's lone pair.

Offline Varlam

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Re: Cyanide as a Lewis Base
« Reply #9 on: June 26, 2019, 09:36:48 PM »
Suppose one wished to use a model based on hybridized orbitals.  I would suppose that the unshared pair on the carbon atom are in its sp orbital.  Likewise the unshared pair on nitrogen is in its sp orbital, not an s orbital.

The electronic configuration of nitrogen is:1s2 2s2 2p3
so I think the unshared pair is two electrons on 2s orbital. Correct me If I am mistaken.

The triple bond between carbon and nitrogen has two kinds of bonding.   One bond is formed from the overlap of one sp orbital on carbon with an sp orbital on nitrogen.  This bond has greatest electron density along the internuclear axis.  Each of the two other bonds results from side-by-side overlap of a p orbital on carbon with a p orbital on nitrogen.  That leaves one more sp orbital so far unaccounted for on each atom.  One sp orbital is where the lone pair on nitrogen is, and one sp orbital is for carbon's lone pair.

I assumed that nitrogen does not undergo sp hybridization or any hybridization at all, because its electron configuration of valence shell is:
2s2 2px1 2py1 2pz1
so how will it form sp hybridization regarding its electron configuration? So you mean 2s and 2px hybridize?
 

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