# How many isomers exist for C_5H_10?

A formula of ${C}_{5} {H}_{10}$ has ${1}^{\circ}$ of unsaturation. What does this mean? It means that in comparison to the saturated formula, ${C}_{5} {H}_{12}$, this formula has $2$ hydrogens fewer. A degree of unsaturation specifies an unsaturated bond OR a ring.
So I can make at least 4 olefins with this formula (one of which has a geometric isomer); given the formula, the double bond can be either at $C 1$ or $C 2$.