How Many Stereoisomers Do Hexadecanoic Acid and Oleic Acid Have?

[GreatEscapist]

Homework Statement

[/B]
How many distinct stereoisomers exist for the hexadecanoic acid and oleic acid, respectively?
Please choose from one of the following options.

• 1, 1
• 1, 2
• 2, 2
• 2, 4

Homework Equations

None

The Attempt at a Solution

If you look at the following images of hexadecanoic (palmitic) acid, and oleic acid, respectively, I cannot find how they arrive at their answer.
https://upload.wikimedia.org/wikipedia/commons/b/ba/Palmitic_acid.svg

The correct answer is B.

In palmitic acid...where is the stereoisomer? I would be looking for something that is either cis/trans or R/S...and none of the sp3 carbons have a stereocenter (they all have at least two H's), and the only double bond is on the carboxylic oxygen. Even if you assume that it is resonant with the hydroxyl group, the CH2 group will freely rotate and not cause any fixation. So I do not see where the stereocenter is..

In oleic acid, I can see that there is one cis/trans site, but otherwise I have the same issue.

Why is the carboxylic acid counting as a stereocenter...?

 

[Borek]

Must be some error, no stereoisomers here.

 

[GreatEscapist]

Must be some error, no stereoisomers here.

Thanks, that's what I wanted to confirm. Thanks Khan Academy...

 

[Ygggdrasil]

Cis/trans isomerism is a form of steroisomerism: https://en.wikipedia.org/wiki/Stereoisomerism#Cis.E2.80.93trans_and_E-Z_isomerism

So, B is correct. Palmitic acid contains no stereocenters, so there is only 1 isomer. Oleic acid has a double bond about which you can have two different arrangements, cis and trans, so there two stereoisomers.

 

[Borek]

Strange, I was always under impression stereoisomerism is other name for chirality. Seems I was wrong.