Naming Carboxylic Acids, E and Z

[Freddy Cadmium]

Can anyone help out with my problem? I've attached an image. The image is meant to be the Z isomer of 2-Chloro-2-butenoic acid. My trouble is that I think it's the E isomer. Am I right or wrong?

[Freddy Cadmium]

I'll explain my thoughts. Z means together and E means opposite for the highest molecular mass groups. Here the COOH and the Cl are the heaviest groups and they are on opposite sides of the C=C bond.

[Paul Robbins]

You need to consider the carbon atoms on each side of the double bond separately.

Start with Carbon 2, the one that has the Cl group and the COOH group attached to it. Apply the priority rules (based on atomic number, not mass) to it. Cl has the highest priority.

Now look at Carbon 3, the one with the methyl group and hydrogen attached to it. Apply the priority rules to it. The methyl group has highest priority.

Now, looking at the double bond as a whole, the highest priority groups are both on the same side of the bond. Therefore, this is a Z isomer.

[Freddy Cadmium]

Thank you so much Paul. At last I understand this! I didn't realize you had to deal with the carbons one at a time, which this was making all my reasoning go haywire.

[Paul Robbins]

You're welcome Freddy.