# Isocyanides undergo addition reactions, but cyanides do not. Why?

My book mentions addition reactions of isocyanides with halogens, ozone, sulphur, etc. but it doesn't mention any such reaction for cyanides. Instead, it bluntly states: "Cyanides do not undergo addition reactions". My question is: why is this so? I understand the structures of the ions, but am unable to relate the exact correct logic in this situation.

Here are the addition reactions of isocyanides I am talking about:

\begin{align} \ce{R-NC + O3 &->RNCO + O2}\text{(methyl isocyanate)}\\ \ce{R-NC + 2HgO &-> RNCO + Hg2O}\text{ (methyl isocyanate)}\\ \ce{R-NC + S &-> RNCS} \text{ (methyl isothiocyante)}\\ \ce{R-NC + Cl2 &-> RNC\cdot Cl2} \text{ (methyl imino carbonyl chloride)}\\ \end{align}

• I would think that the nitrogen in cyanide is much less nucleophilic than the carbon in isocyanide, from the look at their resonance structures and how much they might contribute to the real structure. Maybe some reason along those lines? – ralk912 Mar 15 '18 at 3:41
• @ralk912 Well I wish I knew the reason myself :P if you think you're in the right direction, please consider posting an answer. Thanks! – Gaurang Tandon Mar 15 '18 at 3:56
• Well, with ozone is likely to be through a 1,3-dipolarcycloaddition, but I can't figure out how the ozonolide would collapse. I can't really find many references either, so I'm not confident on the answer. Interesting question for sure. – ralk912 Mar 15 '18 at 3:58