Catalytic Hydrogentation of aldehydes/ketones Watch

chem revision
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whats the mechanism for this reaction.

My best guess is Nucleophilic additon or electrophilic addition

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Gerry-Atricks
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Adding hydrogen across the carbonyl bond-i would guess its similar to formation of a hydroxynitrile with KCN so id guess nucleophilic addition but im not sure
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_NMcC_
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(Original post by chem revision)
whats the mechanism for this reaction.

My best guess is Nucleophilic additon or electrophilic addition

cheers
It would be Nucleophilic addition as the carbon is made extremely Delta +ve due to the presence of the more electronegative oxygen.

So the Carbon itself is made very electrophilic, for that reason, electrophiles wouldn't react with carbonyls. They are repelled. So electrophilic addition would never occur with carbonyls.

Also after the pi-bond breaks and the negative charge is placed on the Oxygen. You would also do a Workup Step at the end.

What does that mean? The negatively charged oxygen requires protonation to form your alcohol. So you would need to add either an Acid or H20 to obtain a source of (H+).

The reducing agent (or reagent that would carry out the 'hydrogenation') would likely be NaBH4 or the more powerful LiAlH4.
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Kozmo
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(Original post by _NMcC_)
It would be Nucleophilic addition as the carbon is made extremely Delta +ve due to the presence of the more electronegative oxygen.

So the Carbon itself is made very electrophilic, for that reason, electrophiles wouldn't react with carbonyls. They are repelled. So electrophilic addition would never occur with carbonyls.

Also after the pi-bond breaks and the negative charge is placed on the Oxygen. You would also do a Workup Step at the end.

What does that mean? The negatively charged oxygen requires protonation to form your alcohol. So you would need to add either an Acid or H20 to obtain a source of (H+).

The reducing agent (or reagent that would carry out the 'hydrogenation' would likely be NaBH4 or the more powerful LiAlH4.
This.

You can also think of it as follows:

Hydrogenation = addition of hydrogen. From a very simplistic perspective, addition of hydrogen is the same as reduction (gain of electrons).

Hence, when hydrogenating an aldehyde or ketone we are reducing them back to their corresponding alcohol (primary alcohol or secondary, respectively). Thus, the reaction must be nucleophilic addition.
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chem revision
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(Original post by _NMcC_)
It would be Nucleophilic addition as the carbon is made extremely Delta +ve due to the presence of the more electronegative oxygen.

So the Carbon itself is made very electrophilic, for that reason, electrophiles wouldn't react with carbonyls. They are repelled. So electrophilic addition would never occur with carbonyls.

Also after the pi-bond breaks and the negative charge is placed on the Oxygen. You would also do a Workup Step at the end.

What does that mean? The negatively charged oxygen requires protonation to form your alcohol. So you would need to add either an Acid or H20 to obtain a source of (H+).

The reducing agent (or reagent that would carry out the 'hydrogenation' would likely be NaBH4 or the more powerful LiAlH4.
very helpful answer, thanks!
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_NMcC_
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(Original post by chem revision)
very helpful answer, thanks!
No probs, practice practice practice.

Chemistry is best learned by treating it like Maths. Learn the rules and the reasons why you use them, then apply them to lots of unseen situations i.e Past Paper Questions!
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