[IShouldBeRevising_]

CH3CHCHCH2COOH

This above alkene has two stereo isomers but in the ocr chemistry text book it says to have a stero isomer (e.z) the two highest priority groups must be on the same size. In the above alkene the Z isomer has the Hydrogen's on the same side but hydrogen has atomic number 1 which is the lowest atomic number from all the groups, does any one know why it is a z isomer then?

[dongonaeatu]

Because the alkyl groups are on the same side

[IShouldBeRevising_]

(Original post by dongonaeatu)
Because the alkyl groups are on the same side

It's only got one alkly group, the other is a carboxylic acid?

[dongonaeatu]

(Original post by IShouldBeRevising_)
It's only got one alkly group, the other is a carboxylic acid?

its z isomer because the groups off the carbon chain are both either at the top or at the bottom which contain a C

[illusionz]

The highest priority (in this case biggest) groups are on the same side.

[IShouldBeRevising_]

(Original post by illusionz)
The highest priority (in this case biggest) groups are on the same side.

So when it says highest priority it means either the biggest groups or the groups with the highest atomic number?

[illusionz]

(Original post by IShouldBeRevising_)
So when it says highest priority it means either the biggest groups or the groups with the highest atomic number?

It's not quite that simple

[charco]

(Original post by IShouldBeRevising_)
So when it says highest priority it means either the biggest groups or the groups with the highest atomic number?

Cahn, Ingold, Prelog
Here's a little animated thingy to help explain the priority rules