= Solution
An intense band near $2088\,\mathrm{cm^{-1}}$ is consistent with the high-frequency coupled C–N–N stretching motion of a <diazo group>, with substantial N–N multiple-bond character. It lies above a typical isolated C=N double-bond stretch, and supports contributions with a strong N–N connection. It does not establish that the molecule is a literal localized C–N single bond plus an unperturbed N≡N triple bond: a <normal mode> moves the coupled framework, and the <resonance contributors> describe one electronic structure.
Protonation at the nucleophilic <carbon> gives \b[<methyldiazonium>, $\mathrm{CH_3-N^+\equiv N}$]. The carbon-rich <highest occupied molecular orbital> and the carbon-negative <resonance contributor> rationalize this site. Subsequent displacement of <molecular nitrogen> can be strongly favourable; the initial protonation product still contains both nitrogens.
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