We understand that species with weird electron counts such together nitrogen dioxide (having odd electrons) dimerise come acheive better stability. The structue that $\ceHNC$ is $\ceH-N#C$. Therefore why it does no dimerise?
The usual rule is one concern per short article unless strong related; while your questions are not really connected I’ll still answer both of them since it’s only two.
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Why is $\ceHCN$ no a base?
Well — the is a base. Girlfriend seem to be thinking that gift an acid and being a base is a dichotomy for part reason; rest assured that aside indigenous the very basic Arrhenius concept no acid-base concept predicts the bases can not be acids and also vice-versa.
You correctly allude out the there is a lone pair ~ above nitrogen, and also that lone pair can indeed act as a (Brønsted-Lowry) base. The just ‘difficulty’ is the the carbon side of the $\ce^-C#N$ reality is more basic than the nitrogen side; thus protonation will occur on carbon first.
$$\ceH-C#N^+-H H-C#N + H+ ^-C#N + 2 H+\tag1$$
Equation $(1)$ shows the complete acid-base equilibrium.Why is $\ceNCH$ not an odd-electron compound?
I take it the liberty that rephrasing your 2nd question. If you count electrons as is done in equation $(2)$, you will certainly realise the $\ceCNH$ comes in at ten electrons — an also number — as with $\ceHCN$.
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$$\sum n_\cee- = n_\cee-(\ceC) + n_\cee-(\ceN) + n_\cee-(\ceH)= 4 + 5 + 1 = 10\tag2$$
When writing the Lewis structure, you have to remember official charges. Indeed, your description of $\ceCNH$ is bad; instead you should write the Lewis framework as $\ce^-C#N^+-H$. All valences space satisfied, over there is no reason for the link to dimerise. Assuming 5 electrons to it is in on nitrogen (and thus four to it is in on carbon) would certainly generate a an extremely unstable diradical which would violate the octet rule in a bad way (nine electron on nitrogen). Reduced electron counting violations that the octet preeminence are fine however going over the electron counting for a key group element does not happen.
However, over there is a great tendency for the compound to de- and reprotonate as composed in equation $(3)$: