According to https://www.researchgate.net/publication/6642597_A_generally_applicable_method_for_assessing_the_electrophilicity_and_reactivity_of_diverse_nitrile-containing_compounds, cyanamides (compounds with a N-C≡N group) are more electrophilic than aliphatic nitriles (C-C≡N).
For reference, see the electrophilicity scale on Figure 3 on the link provided. In this scale, you can see a cyanamide marked with an 8, and an aliphatic nitrile as the first structure to the left.
Now, shouldn't the presence of an electron-donating N atom make the nitrile less electrophilic? Compare this to the amide x ketone example usually taught in organic chemistry. Also, notice on Figure 3 that the aromatic rings get progressively more electron-deficient as we move from left to right.
I have thought of two possible explanations:
- The presence of the N leads to delocalization, which in turn would make the cyanamide a "softer" electrophile (important: this scale on Figure 3 refers to a reaction with a thiol).
- A CN group has two pi bonds, so the nitrogen's +R resonance effect happens on one pi bond, while the nucleophilic attack happens on the other, effectively making the N a -I group. In other words, while a nitrile would have two degenerated LUMOs, the cyanamide has one with less energy (due to the +R effect from N) and one with more energy (due to the -I effect).
