How many straight-chain isomers are there of hexene, C_6H_12?

Apr 29, 2015

Five isomers

The double bond may be between carbon 1 and 2, or 2 and 3, or 3 and 4. If the double bond is between carbon 2 and 3 or 3 and 4 there are 2 geometric isomers for each case (cis- and trans)

May 2, 2015

There are 5

Explanation:

Of course, there are no straight chain answers, because most bonds rotate around the $\text{C}$-atoms, except for the double bonds, and even those are not straight.

These bonds can be between $\text{C}$1=$\text{C}$2, $\text{C}$2=$\text{C}$3 and $\text{C}$3=$\text{C}$4.
(The others are mirror-images if you count from the other side of the chain.)

Now, with every double bond, there are two possibilities: cis or trans

If the rest of the molecule is on the same side it's called cis: if not then it's called trans: For the double bond between $\text{C}$1=$\text{C}$2 this doesn't make a difference, but for the other two, there are two possibilities, bringing the total to five.

Another way of showing if a molecule is cis or trans is using *E-Z notation*.

(Pictures from Wiki of the two possibilities of but-2-ene)