# How are alkenes named?

Jul 23, 2018

Well, what is standard operating procedure....

#### Explanation:

For a given olefin, as normal we identify the LONGEST carbon chain:

${H}_{3} \stackrel{1}{C} - C H = C H - \stackrel{4}{C} {H}_{3}$

...the numbering is unambiguous here, and so we gots $\text{2-butylene}$...but for …

${H}_{3} \stackrel{1}{C} - C H = C H - \stackrel{4}{C} {H}_{2} C {H}_{3}$...we choose to number such that the functional group has the LEAST number...and so the former is $\text{2-pentylene}$.

But of course both rings and olefinic bonds, sites of unsaturation, introduce another level of complexity...I could have...

...or....

Because the geometry is different while the carbon-carbon connectivity is the same, these are geometric isomers, that have different chemical and physical properties...