jacksonmeg
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Hi, I need help to determine which compound is most susceptible to reduction by NaBH4, I thought it would be (a) because the others have carbonyl carbons connected to more electronegative atoms which would strengthen the C=O bond?
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charco
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(Original post by jacksonmeg)
Hi, I need help to determine which compound is most susceptible to reduction by NaBH4, I thought it would be (a) because the others have carbonyl carbons connected to more electronegative atoms which would strengthen the C=O bond?
I would go for (a) as alll of the others are capable of developing a molecular orbital covering the carbonyl carbon and the adjacent atom.
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jacksonmeg
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(Original post by charco)
I would go for (a) as alll of the others are capable of developing a molecular orbital covering the carbonyl carbon and the adjacent atom.
is this like a resonance structure where the double bond can move between oxygen atoms?
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charco
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(Original post by jacksonmeg)
is this like a resonance structure where the double bond can move between oxygen atoms?
A delocalised orbital involving the pi system of the carbonyl interacting with the lone pair of the alpha nitrogen or oxygen.

I don't say this for a fact in these cases, but it does happen in peptides (amides) where the carbonyl is adjacent to the nitrogen which then adopts a planar sp2 hybridisation to allow suitable overlap of the lone pair.
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username913907
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(Original post by jacksonmeg)
Hi, I need help to determine which compound is most susceptible to reduction by NaBH4, I thought it would be (a) because the others have carbonyl carbons connected to more electronegative atoms which would strengthen the C=O bond?
The bond will be strongest in the ketone! It's the fact that the other groups reduce the electrophilicity of the Carbonyl carbon which makes NaBH4 unsuitable for some of them
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jacksonmeg
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(Original post by JMaydom)
The bond will be strongest in the ketone! It's the fact that the other groups reduce the electrophilicity of the Carbonyl carbon which makes NaBH4 unsuitable for some of them
why is the ketone the strongest bond? I was told a carbonyl carbon next to an more electronegative element would make the bond stronger...
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username913907
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(Original post by jacksonmeg)
why is the ketone the strongest bond? I was told a carbonyl carbon next to an more electronegative element would make the bond stronger...
True for only inductive withdrawing groups but these have lone pairs that donate into the pi* and weaken the bond, i.e. amide carbonyl is weaker than ketone. We can see this in the differences between the IR stretching frequencies for these groups.
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