Van't Hoff's Models

From WikidChem

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Slide 15

Van't Hoff developed a set of cardboard models, which he used to explain the tetravalence implications of the tetrahedral orientation of the four valences of carbon. The different colored corners represented different substituents. One set of touching vertices represented a single bond. Two shapes comparable to Ladenburg's Benzene are circled. These models also helped determine what molecules were superimposable. He distributed such model sets freely to those interested in understanding his novel ideas, and in the German version of his brochure he supplied patterns to enable readers to make their own.

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Slide 16

With the cardboard models, two touching vertices (which is equivalent to one touching side) signafies a double bond. Fumaric acid is shown on the left, and maleic on the right. Both have a double bond in the middle between two carbons, which cannot rotate. Fumaric acid has a trans set-up, meaning the COOH groups are on opposite sides, while maleic has a cis set-up, which means the COOH groups are on the same side of their respective carbons. The substances are achiral because of the double bond.