If a research paper appeared reporting the structure of a new molecule with formula C2H8, most chemists would be highly skeptical. Why?

Answer: The formula does not correlate with the general molecular formula of any known homologous series of hydrocarbon compounds

Explanation:

Hydrocarbons are arranged in families of compounds known as homologous series, each having its unique molecular formula.

Alkanes CnH2n+2

Alkenes CnH2n

Alkynes CnHn

C2H8 does not fit into any of these homologous series. The compound cannot be cyclic because it has only two carbon atoms. Considering all these, the existence of this hypothetical compound is simply an impossibility.