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Tools of the trade: 3-dimensional structures

Organic compounds are 3‐dimensional and their shape depends on the preferred spatial arrangement of the covalent bonds. The shape of organic compounds are best viewed with the aid of molecular models.

To represent the 3‐dimensional shape on paper, we use hashed and wedged lines. A hashed line points behind the plane of the paper, the wedged line points in front, as shown here for methane.

Methane has a tetrahedral shape, with carbon in the centre and the four hydrogen atoms pointing to the corners of a triangularly‐based pyramid. All the bond angles are around 109°.

tetrahedral

The structure gets more complicated for larger molecules. For butanal, like for methane, we see that three carbon atoms have a tetrahedral shape, but the one in the aldehyde functional group (the purple carbon) is different. It has a trigonal planar, or flat, shape – with the aldehyde carbon in the centre, and oxygen, hydrogen and another carbon pointing to the corners of an equilateral triangle. The bond angles are 120°.

trigonalplanar

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This article is from the free online course:

Exploring Everyday Chemistry

University of York

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