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Chemistry · Glossary

What is Representations?

Also known as: Cram representation · Newman projection · Fischer projection

Definition 16.2 University Chemistry — Year 1 · Chapter 16 — Stereochemistry in Depth

In the Cram representation two bonds are drawn in the plane of the page, a solid wedge points towards the reader and a hashed wedge away. A Newman projection views a molecule along one C–C bond: the front carbon is a point where its three other bonds meet, the rear carbon a circle from whose rim its bonds emerge. In a Fischer projection the carbon chain is vertical, horizontal bonds point towards the reader and vertical bonds away; each crossing is a stereogenic carbon.

Left: Newman projections of ethane along its C–C bond, staggered (rear bonds between the front ones) and eclipsed (rear bonds hidden behind the front ones, drawn slightly offset). Right: the same molecule, (R)-lactic acid, as a Fischer projection and in Cram representation (the vertical bonds of the Fischer cross point away from the reader, the horizontal ones towards the reader).
Left: Newman projections of ethane along its C–C bond, staggered (rear bonds between the front ones) and eclipsed (rear bonds hidden behind the front ones, drawn slightly offset). Right: the same molecule, (R)-lactic acid, as a Fischer projection and in Cram representation (the vertical bonds of the Fischer cross point away from the reader, the horizontal ones towards the reader).
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