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E-Z isomerism

Can someone explain why this is z?
Isomer.jpg4.6KB
Original post by Super199
Can someone explain why this is z?


Both of the higher priority groups are on the 'zame side' (good way to remember it sadly...).

CH3CH2 and CH2OH have higher mass numbers than the H and the CH3 on the other side, so they have 'higher priority, and as they're on the same side, it's a Z-isomer.
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Super199
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Original post by Peppercrunch
Both of the higher priority groups are on the 'zame side' (good way to remember it sadly...).

CH3CH2 and CH2OH have higher mass numbers than the H and the CH3 on the other side, so they have 'higher priority, and as they're on the same side, it's a Z-isomer.

Ok what about this one why isn't it Z as well? Surely the two highest Mr values are on the right side?
x.jpg6.1KB
Original post by Super199
Ok what about this one why isn't it Z as well? Surely the two highest Mr values are on the right side?


Yes, they are on the RHS, but you only name the E/Z isomerism based on the groups above and below the carbons (A.K.A on either side of the carbon-carbon double bond).

Here's a better explanation of it, however it says you should base it on atomic number instead of mass (I was taught mass, so idk).

http://www.chemguide.co.uk/basicorg/isomerism/ez.html
Original post by Super199
Ok what about this one why isn't it Z as well? Surely the two highest Mr values are on the right side?


The priority group on the LHS is at the top.
The priority group on the RHS is at the bottom.

Check out this Cahn Ingold Prelog interactive
Reply 5
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cofio
6
Priority is based on atomic number first (only mass number for isotopes of the same element).

You look at the atoms directly bonded to each C of the C=C. In your examples these are often both Carbon. In this case you go to the next atoms bonded to these. When you have CH2CH2Cl and CH2Cl the next atoms in the second one include Cl which is higher atomic number than the C which is next in the first chain. This makes CH2Cl higher priority even though it is a smaller group.

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