1975 Nobel Prize in Chemistry(2)
Reason for Award
for his research into the stereochemistry of organic molecules and reactions
Laureates
Switzerland
Explanation
A right hand and its mirror image left hand cannot be perfectly overlapped; some molecules behave the same way. Dr. Prelog created a “name tag” system to tell which hand-like shape a molecule has. With this tag, scientists can avoid using the wrong shape when making medicines and other products. As a result, products have become safer and more effective.
Related Keywords
CIP system
The Cahn–Ingold–Prelog rules are the international standard for describing stereochemistry of chiral centers and double bonds with R/S and E/Z symbols. Substituents are ranked by atomic number and the spatial arrangement is then assigned. The system removes ambiguity in stereochemical descriptions, greatly reducing misunderstandings in papers and patents. Chemical software and databases include automatic CIP algorithms. Prelog was a key co-author of the rules.
absolute configuration
Absolute configuration denotes the precise spatial arrangement of substituents around a stereocenter. The R and S enantiomers are mirror images and often have different biological activities. It can be determined experimentally by X-ray crystallography or circular dichroism, but can also be assigned on paper using CIP rules. Accurate specification is essential for quality control and patent protection. Prelog’s systematization organized this field.
stereoisomer
Stereoisomers are compounds with the same molecular formula and bonding order but different spatial arrangements of atoms. They include enantiomers and diastereomers. Melting point, optical rotation and biological activity can differ greatly among stereoisomers. Stereoselective synthesis is the means to control these properties. Prelog’s theories systematized the classification and nomenclature of stereoisomers.
asymmetric synthesis
Asymmetric synthesis introduces chiral elements into a reaction system to preferentially produce one enantiomer or diastereomer. Chiral catalysts, auxiliaries and enzymes are commonly used. It is crucial in industrial production of drugs and fragrances. Prelog’s “prochiral face” concept became a common language for reaction design. Asymmetric synthesis is also a key technology in green chemistry.
conformational analysis
Conformational analysis studies the rotational isomers that a molecule can adopt and the energy differences among them. Steric and stereoelectronic effects influence reactivity. Prelog showed correlations between conformation and reaction rate in norbornane and cyclohexane derivatives. Conformational analysis is important in molecular recognition and material design. Today it is complemented by quantum-chemical calculations.
chiral center
A chiral center is an atomic position, such as an sp3 carbon with four different substituents, that gives rise to mirror-image molecules. Whether the center is R or S alters overall molecular properties. Prelog’s prioritization method lets chemists assign R/S easily on paper. Molecules with chiral centers are selectively recognized in living systems, making them crucial in drug design. In multi-chiral-center systems, interactions create complex stereochemical effects.