How many isomers exist for #C_5H_10#?

1 Answer
anor277
Feb 6, 2016

Not counting geometric isomers, I can count at least 9 isomers. There may be more.

Explanation:

A formula of #C_5H_10# has #1^@# of unsaturation. What does this mean? It means that in comparison to the saturated formula, #C_5H_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 #C1# or #C2#.

Given a ring junction, there are 5 alicyclic structures possible: a five-membered ring; a four-membered ring; and 3 three-membered rings. One of the three-membered rings can have geometric isomers.

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