Isomers: Cyanic Acid and Fulminic Acid
Low-temperature photolysis of solids containing HNCO has been shown to make H-O-C≡N, known as cyanic acid or hydrogen cyanate; it is a tautomer of isocyanic acid. Pure cyanic acid has not been isolated, and isocyanic acid is the predominant form in all solvents. Note that sometimes information presented for cyanic acid in reference books is actually for isocyanic acid.
Cyanic and isocyanic acids are isomers of fulminic acid (H-C=N-O), an unstable compound.
Read more about this topic: Isocyanic Acid