Tautomerism is a phenomenon where a single chemical compound tends to exist in either two or more structures of interconvertible type, which are different considering the relative position of one atomic nucleus i.e. hydrogen, in general. The two structures are known as tautomers. These types of isomer compounds only differ usually in the number of electrons and protons. They also exist in the dynamic equilibrium.
In nitroethane, alpha hydrogen is labile and it forms nitrolic acid and can be explained through below diagram: