[monarchus]

may i ask what is the condition for a molecule to exhibit geometric isomerisme?

I took the a) and b) below from two different exercise books,
a)the molecule has 2 same groups bonded at 2 different double bonded carbon atoms
b)each carbon atom in C=C must be bonded to 2 different atoms or groups


but in one of the exercise books shows that a geometric isomer is not necessary to have 2 same groups bonded at 2 different double bonded carbon atoms, in fact, the both the C=C carbon bonded to 4 different atom, and it says it is a geometric isomer.

so i am confuse, please help.

thank you.

[azmanam]

Start here:

http://www.cem.msu.edu/~reusch/VirtTxtJml/sterisom.htm#isom1
http://www.usm.maine.edu/~newton/Chy251_253/Lectures/Geometric%20Isomers/GeometricIsomers.html

Your first definition describes the relationship between two molecules (as opposed to within the same molecule), and the second definition describes the relationship within the same molecule, I think.  Although, I don't think those are very good one-sentence descriptions of geometric isomerism.

[monarchus]

Start here:

http://www.cem.msu.edu/~reusch/VirtTxtJml/sterisom.htm#isom1
http://www.usm.maine.edu/~newton/Chy251_253/Lectures/Geometric%20Isomers/GeometricIsomers.html

Your first definition describes the relationship between two molecules (as opposed to within the same molecule), and the second definition describes the relationship within the same molecule, I think.  Although, I don't think those are very good one-sentence descriptions of geometric isomerism.

Firstly, thank you for your help.

But, i do not understand the explanations in the given websites, it is "too deep into the topic" for me now, nor do i understand the explanation you had given me. I am sorry...

So, is there is simpler way to explain it?

Thank you.

[azmanam]

To strictly answer the question you asked, the conditions for geometric isomerism are as follows:


1) restricted rotation about a bond (either a double bond or a bond in a cyclic ring system)
2) The groups on one carbon atom of the bond with restricted rotation need to be differentiable from each other, that is not the same. 
3) The groups on the other carbon atom of the bond with restricted rotation need to also be differentiable from each other - however they can be the same as the groups on the first carbon atom

That is all that is strictly needed to satisfy the conditions for a geometric isomer.

[monarchus]

To strictly answer the question you asked, the conditions for geometric isomerism are as follows:


1) restricted rotation about a bond (either a double bond or a bond in a cyclic ring system)
2) The groups on one carbon atom of the bond with restricted rotation need to be differentiable from each other, that is not the same. 
3) The groups on the other carbon atom of the bond with restricted rotation need to also be differentiable from each other - however they can be the same as the groups on the first carbon atom

That is all that is strictly needed to satisfy the conditions for a geometric isomer.

Thank you.