It was not until after the observations of certain molecular phenomena that stereochemical principles were developed. In 1815, Jean-Baptiste Biot’s observation of optical activity marked the beginning of organic stereochemistry history. He observed that organic molecules were able to rotate the plane of polarized light in a solution or in the gaseous phase.[1] Despite Biot's discoveries, Louis Pasteur is commonly described as the first stereochemist
^Nasipuri, D (2021). Stereochemistry of Organic Compounds Principles and Applications (4th ed.). New Delhi: New Age International. p. 1. ISBN978-93-89802-47-4.
The application of stereochemistry to biological macromolecules has allowed for the study of the structure and properties of polymers of biological origin. In regards to the degradation of starch and cellulose, D-glucose is produced by different intermediates which are stereoisomers of each other.[1]
Fischer projectionAn important branch of stereochemistry is the study of chiral molecules, which are molecules that lack a plane of symmetry and are, therefore, not superimposable on their mirror images. The term chiral stems from the Greek word "cheir," meaning handedness and describes objects that have a "left-handed" and "right-handed" form. Molecules are considered to be chiral if they contain an asymmetric carbon atom, which is attached to four different substituents that form a tetrahedron.[1] The idea of chirality is essential for explaining the concept of stereoisomerism. Compounds that have the same molecular formula, but differ in the spatial arrangement of their atoms are stereoisomers. Based on arrangement, these compounds can be categorized as either enantiomers or diasteriomers. Enantiomers are pairs of stereoisomers that are non superimposable mirror images of each other. Comparably, diasteriomers are stereoisomers that are superimposable on each other and are not mirror images. Stereoisomers that do not involve chirality are geometrical isomers, also known as cis-trans isomers, which exist as a result of restricted rotation around a double bond within a molecule. When two of the same atoms are attached to the same side of the molecule, a cis isomer is present. Conversely, when two of the same atoms are attached to opposing sides of the molecule, a trans isomer is present. Another type of stereoisomerism is conformational stereoisomerism. These isomers exist as a result of rotation around the central carbon-carbon bond within a molecule and are constantly being interconverted into its different isomers at room temperature. The possible conformational isomers are gauche (60°), anti (180°), and eclipsed (0°).[2]
^Morris, David. Stereochemistry (vol. 1 ed.). Royal Society of Chemistry. pp. 19–24. ISBN978-0471224778.
^Brown, William (2022). Organic Chemistry (9th ed.). Cengage. ISBN978-0357451861.
add section on representation of stereochemical structures
Wedge and dash diagrams are used to represent 3-dimensional molecules on paper and are often used to depict the stereochemistry of chiral molecules. Dashed wedges are used to show bonds that project behind the plane of the paper and dark, shaded wedges are used to show bonds that project out of the plan of the paper. The ordinary lines are used to show bonds that are in the plane of the paper. [1]
Fischer projections are a simplified way to represent 3-dimensional stereochemical molecules in 2-dimensional layout. All of the bonds are drawn as ordinary lines that intersect at 90°.[1] The top and bottom lines represent the front and back of the molecule, respectively. One side line represents a dashed wedge and the other represents a dark wedge.
Sawhorse projections are used to view molecules from an angled perspective instead of a side view. The parallel bonds represent eclipsed conformations and all anti parallel bonds can represent either gauche or anti conformations.[2]
Newman projections are used to visualize molecules from front to back along a carbon-carbon bond.[2] The carbon closest to the viewer is the front carbon and the one furthest away is the back carbon. The three atoms attached to the front carbon are depicted as being attached to the center of a circle and the atoms attached to the back carbon are shown as coming from behind the circle. Newman projections are often used as a simplified version of sawhorse projections.
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