Question

Why are alkenes, alkanes, and alkynes with 5 carbon atoms each not considered isomers?

Answer 1

See below...

Explanation:

For the compounds to be isomers they must have identical condensed formula.

Alkane with `n` `C` atoms : `C_nH_(2n+2)`

Alkene with `n` `C` atoms : `C_nH_(2n)`

Alkyne with `n` `C` atoms : `C_nH_(2n-2)`

The compounds clearly differs in the number of `H` atoms per molecule and hence cannot be considered as isomers.