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Cis-trans (E,Z) isomerism

Examples

Fumaric acid

It is a white solid that can be extracted from the fumitory (or earth smoke):

Maleic acid

It is a white solid that can be extracted from pumpkin:

The prefixes cis and trans

Cis (= on this side) and trans (= on the other side) come from the Romans who made a distinction between their fine world and the world of infamous barbarians who were "on the other side".

Chemistry makes the distinction by these prefixes between groups which are on the same side of the C = C axis and groups which are located on either side of it:

Example: Maleic acid = cis-butenedioic acid Fumaric acid = trans-butenedioic acid

The prefixes (Z) et (E)

Z (= Zusammen, together) and E (= Entgegen, opposite) come from the German.

Example: Maleic acid = (Z)-butenedioic acid Fumaric acid = (E)-butenedioic acid