Previously, I pondered about the strange N=N double bond in nitrosobenzene dimer[1] as a follow up to commenting on the curly arrow mechanism of the dimerisation.[2] By the same curly arrow method, one can produce the below, showing how the simpler nitric oxide radical could potentially dimerise to a species with a N≡N triple bond!† This involves a total of six electrons entering the N-N region, and hence raises the question of whether these all move in a single concerted/synchronous bond forming reaction, or whether they might go in (asynchronous) stages. Here are some calculations[3]) which might shed some light on this aspect.
References
- H. Rzepa, "The mysterious N=N double bond in nitrosobenzene dimer.", 2025. https://doi.org/10.59350/rzepa.29383
- H. Rzepa, "Mechanism of the dimerisation of Nitrosobenzene.", 2025. https://doi.org/10.59350/rzepa.28849
- H. Rzepa, "N2O2 as strong dimer TS as biradical cis, G = -259.785500", 2025. https://doi.org/10.14469/hpc/15483