The acetonitrile anion (CH₂CN–) can be represented with various resonance structures, which illustrate the distribution of the negative charge. Here’s one way to depict it:
Resonance Structure:
H H
\
C ⇌ H
/ \ /
H C C
| ||
H----C N-
In this representation, we have shown the negative charge on the nitrogen atom, which is more electronegative than carbon. This allows for greater stability when the negative charge is delocalized. The first structure shows the negative charge localized on the carbon atom, while the second structure delocalizes the charge onto the nitrogen. The ability to distribute the charge across multiple atoms enhances the stability of the anion through resonance.
Acidity of Nitriles: Nitriles, like acetonitrile, exhibit acidity mainly due to the presence of the strong C≡N bond. When nitriles lose a proton (H+), they can form a corresponding anion, in this case, the acetonitrile anion, which benefits from resonance stabilization. The negative charge is adequately supported by the electronegative nitrogen, making the loss of hydrogen easier, thereby increasing the acidity of nitriles compared to other organic compounds. Additionally, the resonance structures help to delocalize the negative charge, further stabilizing the anionic species and allowing nitriles to act as relatively weak acids.