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Single electron reduction of ketone by Na or Zn
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Al Grayson
Single electron reduction of ketone by Na or Zn
Let the carbonyl compound under consideration be acetone.
Case I: Hydrogen Abstraction
The species formed are NaH and an allyl-type radical. The resonating system includes an electronegative oxygen atom, which also has an incomplete octet in one of the canonical forms.
In essence, products are not really stable.
Case II: Attack on Carbonyl
The species formed is a radical anion, which are relatively stable as the filled orbital of the oxygen relieves some electron deficiency of the radical. This effect is stronger than the one offered the pi-bond in Case I.
Let the carbonyl compound under consideration be acetone.
Case I: Hydrogen Abstraction
The species formed are NaH and an allyl-type radical. The resonating system includes an electronegative oxygen atom, which also has an incomplete octet in one of the canonical forms.
In essence, products are not really stable.
Case II: Attack on Carbonyl
The species formed is a radical anion, which are relatively stable as the filled orbital of the oxygen relieves some electron deficiency of the radical. This effect is stronger than the one offered the pi-bond in Case I.
I would suspect that this is kinetically controlled. So Im not entirely convinced by an argument based on relative product stability. If I had to take a guess Id say that it is simply because the electron adds into the LUMO of the carbonyl compound, which is the C=O π* (and not the C–H σ*). But Im not confident enough to post it as an answer.More
Let the carbonyl compound under consideration be acetone.
Case I: Hydrogen Abstraction
The species formed are NaH and an allyl-type radical. The resonating system includes an electronegative oxygen atom, which also has an incomplete octet in one of the canonical forms.
In essence, products are not really stable.
Case II: Attack on Carbonyl
The species formed is a radical anion, which are relatively stable as the filled orbital of the oxygen relieves some electron deficiency of the radical. This effect is stronger than the one offered the pi-bond in Case I.
Let the carbonyl compound under consideration be acetone.
Case I: Hydrogen Abstraction
The species formed are NaH and an allyl-type radical. The resonating system includes an electronegative oxygen atom, which also has an incomplete octet in one of the canonical forms.
In essence, products are not really stable.
Case II: Attack on Carbonyl
The species formed is a radical anion, which are relatively stable as the filled orbital of the oxygen relieves some electron deficiency of the radical. This effect is stronger than the one offered the pi-bond in Case I.
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