Coming from ALKENES
=Alkenes and Geometric Isomers= We have briefly covered what geometric isomers are in the Isomers node. However, for NCEA level 2 you must be able to explain why geometric isomers exist for some alkenes but not for others. ===Generally you must explain these rules:=== 1. The most important requirement is a double C=C bond. This restricts rotation so that groups attached the these carbons cannot change position. 2. The same group must be found on each carbon of the double bond. It could be a simple H atom, a Cl, OH, or a ethyl group (-CH2CH3) - anything! 3. The same group must NOT be found twice on a carbon that is part of the double bond. This would defeat the purpose of cis/trans positions. Take a look at the videos under the tab above for examples. Cis-but-2-ene fulfills all 3 requirements. In this case, there are two separate groups, H and -CH3. These groups are found on each carbon in the double bond, but no group is found twice on the same carbon! [image:]
Credit: Megan Fowler