Page 298 - Academic Press Encyclopedia of Physical Science and Technology 3rd Organic Chemistry

P1: GRB Final Pages Qu: 00, 00, 00, 00
Encyclopedia of Physical Science and Technology EN016B-738 July 31, 2001 14:0

Stereochemistry

Ernest L. Eliel
University of North Carolina

I. Introduction VIII. Structure, Configuration, Notation
II. History. Optical Activity IX. Determination of Configuration
III. Stereoisomerism X. Chirality in Absence of Chiral Centers
IV. Stereoisomerism of Alkenes and Cyclanes XI. Conformation
V. Properties of Stereoisomers XII. Cycloalkanes and their Conformations
VI. Significance XIII. Chiroptical Properties. Enantiomeric Purity
VII. Separation (Resolution) and Racemization of XIV. Prochirality
Enantiomers

GLOSSARY be called chiral if the constituent molecules are chiral,
even if the substance is racemic.
Angle strain Excess potential energy of a molecule Configuration The spatial arrangement of atoms by
caused by deformation of an angle from the normal, which stereoisomers are distinct, but disregarding
e.g., of a C–C–C angle from the tetrahedral. Also called facile rotation about single bonds.
“Baeyer strain.” Conformation The (differing) spatial array of atoms in
Anti or antiperiplanar Conformation of a segment molecules of given constitution and configuration pro-
X–C–C–Y in which the torsion angle (which see) is duced by facile rotation about single bonds.
◦
180 or near 180 . X and Y are said to be anti or an- Conformers Stable conformations (located at energy
◦
tiperiplanar (to each other). minima). Isomers which differ by virtue of facile ro-
Cahn–Ingold–Prelog (C-I-P) Descriptors Descriptors tation about single bonds, usually readily intercon-
R and S (and others) used to describe the spatial ar- vertible.
rangement (configuration) of ligands at a chiral center Constitution(ofamolecule) Thenatureofitsconstituent
or other chiral element (chiral axis, chiral plane). atoms and their connectivity.
Chiral center An atom to which a C-I-P descriptor can Diastereomers (diastereoisomers) Stereoisomers that
be attached, usually a group IV (tetrahedral) or group V are not mirror images of each other.
(pyramidal) atom. Reflection of the molecule must re- Eclipsed conformation Conformation of a nonlinear ar-
verse the descriptor. ray of four atoms X–C–C–Y in which the torsion angle
Chirality Handedness; the property of molecules or (which see) is zero or near zero (also “synperiplanar”).
macroscopic objects (such as crystals) of not being su- X and Y are said to be eclipsed.
perposable with their mirror images. Substances may Enantiomer(ic) excess In a partially or completely

79