Why is this not a geometric isomer?

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In summary, the conversation discusses the concept of geometric isomerism and its application to certain chemical compounds. The conversation includes a question about why one particular compound is not considered a geometric isomer, and a discussion about the differences between cis-trans isomers and mirror image isomers. The concept of identity is also mentioned as being essential to understanding isomerism.
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Declan McKeown
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ObccNpv.png


While I'm fairly sure this question is pretty straight forward, I can't remember why (ii) is not considered a geometric isomer. (The answer is (c)) http://imgur.com/ObccNpv

Looking at ii I would have thought it to be trans-pent-2-ene due to the ethyl and methyl group either side of the double bond, however it is not and I am not sure why. Would anyone happen to know why this is?

Thanks :)
 
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Are (i) and (ii) isomers at all?
 
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https://en.wikipedia.org/wiki/Cis–trans_isomerism

Well, (I) and (II) are not geometric isomers because they are the same compound just mirror images, besides both seem trans to me.
I II and III can not be geo. (cis-trans) isomers because that is three options.
III and IV don't make sense because IV is trans so III should be cis but it's weird because its not.

Sorry that's all I can help with my limited knowledge.
 
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IcyRealm said:
https://en.wikipedia.org/wiki/Cis–trans_isomerism

Well, (I) and (II) are not geometric isomers because they are the same compound just mirror images, besides both seem trans to me.
I II and III can not be geo. (cis-trans) isomers because that is three options.
III and IV don't make sense because IV is trans so III should be cis but it's weird because its not.

Sorry that's all I can help with my limited knowledge.

Being mirror images does not necessarily make them the same compound! You probably remember now. :oldsmile:

The essential is you can swivel it around a vertical axis and i coincides with ii - so it is the same thing. Any bodily movement leading one to coincide with another means it is the same thing. A reflection on the other hand is not a bodily movement.

I think that identity was the essential point of this excercise. Anything that has the same composition as another thing but is not the same thing is an isomer of it.
 
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1. Why can't this molecule be a geometric isomer?

Geometric isomers are molecules that have the same molecular formula, but differ in the arrangement of atoms in space. If the molecule has a double bond, it must have two different groups attached to each of the carbon atoms involved in the bond. If this is not the case, the molecule cannot exhibit geometric isomerism.

2. How can I tell if a molecule is a geometric isomer?

To determine if a molecule is a geometric isomer, you must first identify if it has a double bond. Then, check if the groups attached to each carbon atom involved in the bond are different. If they are not, the molecule is not a geometric isomer.

3. Can a molecule have more than one geometric isomer?

Yes, a molecule can have multiple geometric isomers if it has multiple double bonds with different groups attached to each carbon atom involved in the bond. However, if the molecule only has one double bond, it can only have one geometric isomer.

4. Are geometric isomers the same as structural isomers?

No, geometric isomers are a type of stereoisomerism where molecules have the same molecular formula but differ in the arrangement of atoms in space. Structural isomers, on the other hand, have the same molecular formula but differ in the bonding and connectivity of atoms.

5. Why is geometric isomerism important in chemistry?

Geometric isomerism is important in chemistry because it affects the physical and chemical properties of molecules. Different geometric isomers can have different melting points, boiling points, and reactivity, which can have significant impacts in various industries such as pharmaceuticals and materials science.

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