geometric isomers

[deappri]

What are geometric isomers?

iv'e been having trouble understanding what they are and what they are for.

[chenbeier]

There are 2 types of geometric isomers, 'cis' and 'trans'. -cis isomers: when similar groups are present on the same side of the double bonds, then they are termed as cis. - trans isomers: when similar groups are present on the opposite sides of the double bonds then they are called trans isomers. Cis and trans 2- Butene are examples.

[OldChemE]

Geometric isomers are situations where the order of the atom bonds are the same, but where there are more ways than one from a geometry standpoint.  Try this on a piece of paper:  Draw a picture of 1,2,dichloroethane. 

1.  start in the middle with two carbon atoms in a double bond:        C=C

2.  Add chlorine and hydrogen to both sides:  they have to connect either above the C=C or below    ^Cl\_C=C^/Cl           or       ^Cl\_C=C^/H

Notice that I can put either both chlorine atoms above the C=C pair or one chlorine and one hydrogen (the bottom would then be either two hydrogen atoms or a hydrogen and a chlorine).  Thus, we can build the molecule two geometrically different ways.

Does it matter?  Well, for example, natural unsaturated fats are mostly one type of geometric isomer (cis).  When manufacturers hydrogenate fats like vegetable oil to make things like margarine, the process tends to create trans isomers instead of cis isomers-- and there are health risks associated with trans fatty acids.

Edited June 11, 2022 by OldChemE
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