Stereoisomer: 2-methyl-2-pentene

[casualdehyde]

Homework Statement

The compound 2-methyl-2-pentene:

Select one:
a. has no structural or geometric isomers
b. has 2 structural alkene isomers, each of which has an E isomer and a Z isomer form.
c. has 5 structural isomers
d. has 3 structural isomers
e. exists as E and Z isomers

The Attempt at a Solution

So the wording of this question confuses me a bit, I took that when it said the compound 2-methyl-2-pentene it was just talking about c6h12 - if this is not the case and I've understood it horribly wrong please inform me :)

So straight away I cross out A just because it's obvious that at least 1 structural isomer exists. I then eliminate C and D because there are more than 5 structural isomers. I then cross out B because there are more than 2 alkene isomers 1/2/3-hexene eg. So I guess I would go with E as my answer. I know it's an easy question but I always overthink them and end up getting them wrong so this is more to help me understand the question and clear up any misconceptions I may have. Thanks

 

[Borek]

E is definitely not a correct answer, draw the molecule - does it have E, Z isomers?

 

[casualdehyde]

E is definitely not a correct answer, draw the molecule - does it have E, Z isomers?

Damn you're 100% right! I had that originally but then I started to think of the question as talking about all C6H12 molecules. I'm a but confused as what constitutes an isomer in relation to this question - I assume it's not talking about all C6H12 isomers so does that mean it's only taking about the location of the double bond and methyl group? Is it C then? It seems to have a large number of structural isomers to me.

 

[Borek]

TBH, I am not sure what the correct answer is - I don't have time to investigate, and just intuition is not enough. To me it looks like it talks about all C₆H₁₂ molecules.

 

[DeeNos]

!

Your approach is correct. The compound 2-methyl-2-pentene, with the chemical formula C6H12, has three structural isomers: 2-methyl-2-pentene, 3-methyl-1-pentene, and 2-methyl-3-pentene. However, these three isomers can also exist as E and Z isomers, making a total of six stereoisomers. Therefore, the correct answer is E. Well done!