[Eternal_Fire]

Hi all,
I have an assignment in which such a question was asked. This is the only organic chemistry question I have been stuck at. I have been staring at this problem and writing all the possible structures but still can't get all the possible isomers. Any guidance to derive all the possible isomers will be appreciated.

Thanks

Structural isomerism and stereoisomerism should be considered when attempting this question.
How many isomeric compounds with molecular formula C5H6O4 contain two -CO2H groups and one C=C double bond?
A)   5
B)   6
C)   7
D)   8
 

[Borek]

Show structures you got and we will start from there.

You can use SMILES or just draw and attach the image (note: file can't be too large, typical picture taken with mobile is too large, so you will need to edit it and make it smaller).

[Eternal_Fire]

https://imgur.com/a/qPxTv3B

Here you go. I can't seem to think of any others.

[mjc123]

Well, for a start, those aren't -CO2H groups. Conventionally, -CO2H means a carboxylic acid, not a formate ester.

Have you considered branched chain molecules?

[Eternal_Fire]

I fixed that and found a branched one. But I am not sure how it's considered as an isomer

[Borek]

So as far as I can tell you mean these two?





You marked these as having two stereoisomers, can you mark which carbon is the chiral one in both cases?

I am not sure how it's considered as an isomer

What is the isomer definition?

[Babcock_Hall]

Have you thought about the degree of substitution of the vinyl group?

[Eternal_Fire]

I meant cis/trans isomerism firstly. What's degree of substitution?

[Borek]

I meant cis/trans isomerism firstly.

Is it possible for ?

[Babcock_Hall]

The degree of substitution is the number of carbon atoms bonded to the two carbon atoms of the vinyl group.

[Eternal_Fire]

Replying to Mr/Dr Borek: Nope. I overlooked the same h group. I often have trouble seeing patterns in skeletal formula and it's persistent.

Replying to Mr/Dr Babcock Hall: I have not been taught specifically about vinyl group or degree of substitution but rather relative stability of carbocations.

[Babcock_Hall]

All of the structures that you have shown so far are di-substituted with respect to the C=C bond.  What about mono-substituted or tri-substituted molecules?

[Eternal_Fire]

Are these all the possibilities, summing up to 7 in total? Have I drawn any duplicates, and how do I recognize any duplicates in the future?

[Babcock_Hall]

If you name two compounds by IUPAC rules and they have the same name, then they are the same thing.  If they have two different names, then they are different.  The prefixes cis and trans are useful for disubstituted molecules, but they become ambiguous for trisubstituted molecules.  If I am interpreting your drawings correctly, 5 duplicates 2.  I think that one isomer is missing: try putting the two carboxylic acids on the same carbon of the vinyl group. 

[Eternal_Fire]

How do you name this using IUPAC Naming system? Are these all right? 7 isomers as per this