15m0808
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Hi! I was looking at the mechanism of carbonyl with HCN and these questions popped into my mind.

1. Why is aldehyde planar and ketone isn't?
2. How can you tell whether a molecule is planar or not?

Thank you to you all for your help in advance.
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seals2001
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(Original post by 15m0808)
Hi! I was looking at the mechanism of carbonyl with HCN and these questions popped into my mind.

1. Why is aldehyde planar and ketone isn't?
2. How can you tell whether a molecule is planar or not?

Thank you to you all for your help in advance.
Look into molecular geometry
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Pigster
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(Original post by 15m0808)
Hi! I was looking at the mechanism of carbonyl with HCN and these questions popped into my mind.

1. Why is aldehyde planar and ketone isn't?
2. How can you tell whether a molecule is planar or not?

Thank you to you all for your help in advance.
1. Ketones are planar from the point of view of the carbon atom with the double bond to O.
2. Which spec are you studying? Different exam boards have different ways of making things planar.
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15m0808
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(Original post by Pigster)
1. Ketones are planar from the point of view of the carbon atom with the double bond to O.
2. Which spec are you studying? Different exam boards have different ways of making things planar.
I'm doing edexcel!
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qwert7890
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(Original post by 15m0808)
Hi! I was looking at the mechanism of carbonyl with HCN and these questions popped into my mind.

1. Why is aldehyde planar and ketone isn't?
2. How can you tell whether a molecule is planar or not?

Thank you to you all for your help in advance.
1. From what I know, aldehyde and ketone are both planar. Have you read otherwise?

2. The best way to tell the molecular geometry is by the hybridisation around the central atom. If you're familiar with the concept of hybridisation,then you'll realise that in general :

a ) sp = linear = 180 degrees
b ) sp2 = trigonal planar = 120 degrees
c ) sp3 = tetrahedral = 109.5 degrees
d ) sp3d = trigonal bipyramidal = 120 degrees within the trigonal planar, and 90 degrees above and below the plane
e ) sp3d2 = octahedral = 90 degrees

So sp2 is planar, and the 3 trigonal planar atoms within the sp3d are planar.
sp3d2, sp3 --> non-planar

If you've already gone through this topic, the above list should ring a bell. Otherwise, I've just been rambling for no reason
Last edited by qwert7890; 4 weeks ago
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Crunch_chemistry
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The geometry is around a named central atom. With respect to the C, both aldehydes and ketones are planar because there are three areas of electron density surrounding the C atom - whether an area contains 2 or 4 electrons, as in is a single or double bond, is irrelevant
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