Hydrogen isocyanide

Names

IUPAC names

hydrogen isocyanide
azanylidyniummethanide

Other names

isohydrocyanic acid
hydroisocyanic acid
isoprussic acid

Identifiers

3D model (Jmol)

CHEBI:36856^Y

4937885^Y

InChI=1S/CHN/c1-2/h2H^Y

Key: QIUBLANJVAOHHY-UHFFFAOYSA-N^Y
InChI=1/CHN/c1-2/h2H

SMILES

[C-]#[NH+]

Properties

Chemical formula

HNC

Molar mass

27.03 g/mol

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

(what is ^YN ?)

Infobox references

Hydrogen isocyanide is a chemical with the molecular formula HNC. It is a minor tautomer of hydrogen cyanide (HCN). Its importance in the field of astrochemistry is linked to its ubiquity in the interstellar medium.

Both 'hydrogen isocyanide' and 'azanylidyniummethanide' are correct IUPAC names for HNC. Currently there is no preferred IUPAC name. The second one is according to the substitutive nomenclature rules, derived from the parent hydride azane (NH₃) and the anion methanide (C⁻).

Hydrogen isocyanide (HNC) is a linear triatomic molecule with C_∞vpoint group symmetry. It is a zwitterion and an isomer of hydrogen cyanide (HCN). Both HNC and HCN have large, similar dipole moments, with respectively μ_HNC = 3.05 Debye and μ_HCN = 2.98 Debye. These large dipole moments facilitate the easy observation of these species in the interstellar medium.

As HNC is higher in energy than HCN by 3920 cm⁻¹ (46.9 kJ/mol), one might assume that the two would have an equilibrium ratio at T < 100 K of ([HNC]/[HCN])_{eq,T < 100 K} < 10⁻²⁵. However, observations show a very different conclusion; ([HNC]/[HCN])_observed is much higher than 10⁻²⁵, and is in fact on the order of unity in cold environments. This is because of the potential energy path of the tautomerization reaction; there is an activation barrier on the order of roughly 12,000 cm⁻¹ for the tautomerization to occur, which corresponds to a temperature at which HNC would already have been destroyed by neutral-neutral reactions.

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