Organic Chemistry 1 · Resonance and electron distribution
Cyanomethyl anion: carbanion and ketenimine forms
Conditions: No reagent: draw the next resonance contributor of the same species.
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Drag from the electrons that move to where they go, or tap one and then the other. Every arrow is checked; Hint helps when you're stuck. No account needed.
The mechanism, step by step
Next plays each step's curved arrows and explains them. The written steps are below.
Read all 2 written steps
Carbanion lone pair forms C=C
The lone pair on the CH2 carbon becomes a C=C π bond to the nitrile carbon. One of the two C≡N π pairs then moves onto nitrogen so the central carbon still has four bonds.
The curved arrows
- The lone pair on C3 moves into the C2–C3 bond, making a new C=C π bond.
- One π pair of the C≡N triple bond moves onto nitrogen, leaving a C=N double bond and N⁻.
Ketenimine (N⁻) contributor
The second contributor is a ketenimine anion with the charge on nitrogen, which is more electronegative than carbon, so it is an important contributor. This delocalization makes acetonitrile far more acidic (pKa about 31 in DMSO) than ethane and lets nitrile anions act as carbon nucleophiles.
What you'll practice
Use two curved arrows to move the negative charge of the cyanomethyl anion from carbon onto the nitrile nitrogen.
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