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How do projection formulas represent three-dimensional molecules on paper?

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representations of molecular structure — molecule Several methods of representing a molecule's structure. In Lewis structures, element symbols represent atoms, and dots represent electrons surrounding them. A pair of shared electrons (covalent bond) may also be shown as a single dash. The ball-and-stick model better illustrates the spatial arrangement of the atoms. For aromatic compounds, the Kekulé structure is common, in which each bond is represented by a dash, carbon atoms are implied where two or more lines meet, and hydrogen atoms are usually omitted. Bond-line formulas, similar to the Kekulé structure, are often used for complex nonaromatic organic compounds. Sugars are often drawn as Fischer projections, in which the carbon “backbone” is drawn as a straight vertical line, with carbon atoms implied where horizontal lines intersect the vertical one.

Projection formulas are two-dimensional representations used to depict the three-dimensional structure of molecules on a flat surface. These formulas utilize symbols for atoms connected by dashes or curves that represent chemical bonds.1

A common type is the Fischer projection, which employs specific conventions to convey spatial orientation:
* Horizontal lines represent bonds that project out of the plane of the paper toward the viewer.2
* Vertical lines represent bonds that project away from the viewer.2

These formulas are particularly valuable in the study of stereoisomers—compounds that share the same composition but differ in the spatial arrangement of their atoms. By following standardized drawing conventions, chemists can effectively distinguish between different isomers, such as pairs of enantiomers, and they are frequently used to represent sugars.12