Acids Hydrogen Bonds
In the tautomerism of barbituric acid why does only one Hydrogen atom migrates?
If all the three Hydrogen atom migrate in the ring it will obtain an aromatic character and will be more stable. But in the tautomeric structure it shows only one Hydrogen bond migrating and only one double bond formation.
chemical name of Barbituric acid or malonylurea or 4-hydroxyuracyl is Pyrimidine-2,4,6(1H,3H,5H)-trione.
As it has two NH group and three =O attached to the ring, when one Hydrogen is migrated to any of the adjutant =O – it is converted into -OH, and electronic distribution of the ring is changed, and a double bond is formed in the ring. This do not allow to migrate second hydrogen of second -NH group. There is no question of migration of third hydrogen – attached to carbon as it is attached to carbon more strongly then hydrogen on Nitrogen in -NH group.
Barbituric acid is also known as
2,4,6(1H,3H,5H)-Pyrimidinetrione,
2,4,6-Trioxohexahydropyrimidine,
2,4,6-Trihydroxypyrimidine,
2,4,6-Trioxypyrimidine,
2,4,6-Pyrimidinetriol,
2,4,6-Pyrimidinetrione,
Pyrimidinetriol,
2,4,6-Trihydroxy-1,3-diazine, N,N’-Malonylurea,
Malonylurea, 6-Hydroxyuracil, 6-Hydroxy-Hydrouracil,
N,N’-(1,3-dioxo-1,3-propanediyl)urea
Acid Bonding: The Strong & the Weak