Stereochemistry

Stereochemistry, a subdiscipline of

Stereochemistry spans the entire spectrum of organic, inorganic, biological, physical and especially supramolecular chemistry. Stereochemistry includes methods for determining and describing these relationships; the effect on the physical or biological properties these relationships impart upon the molecules in question, and the manner in which these relationships influence the reactivity of the molecules in question (dynamic stereochemistry).

History

It was not until after the observations of certain molecular phenomena that stereochemical principles were developed. In 1815,

Cahn–Ingold–Prelog priority rules are part of a system for describing a molecule's stereochemistry. They rank the atoms around a stereocenter in a standard way, allowing the relative position of these atoms in the molecule to be described unambiguously. A Fischer projection is a simplified way to depict the stereochemistry around a stereocenter.

Thalidomide example

Stereochemistry has important applications in the field of medicine, particularly pharmaceuticals. An often cited example of the importance of stereochemistry relates to the thalidomide disaster.

Many definitions that describe a specific conformer (

• a
  torsion angle of ±60° is called gauche^[11]
• a torsion angle between 0° and ±90° is called syn (s)
• a torsion angle between ±90° and 180° is called anti (a)
• a torsion angle between 30° and 150° or between –30° and –150° is called clinal
• a torsion angle between 0° and 30° or 150° and 180° is called periplanar (p)
• a torsion angle between 0° to 30° is called synperiplanar or syn- or cis-conformation (sp)
• a torsion angle between 30° to 90° and –30° to –90° is called synclinal or gauche or skew (sc)[12]
• a torsion angle between 90° to 150°, and –90° to –150° is called anticlinal (ac)
• a torsion angle between ±150° to 180° is called antiperiplanar or anti or trans (ap).

Torsional strain results from resistance to twisting about a bond.

Types

• Atropisomerism
  An energetic form of axial chirality. This form of chirality derives from differential substitution about a bond, commonly between two sp²-hybridized atoms.^[13]
• Cis–trans isomerism
  Also referred to as geometric isomers, these compounds have different configurations due to the inflexible structure of the molecule. Two requirements must be met for a molecule to present cis-trans isomerism:^[14]
  1. Rotation within the molecule must be restricted.
  2. Two nonidentical groups must be on each doubly bonded carbon atom.
• Conformational isomerism
  This form of isomerism is also referred to as conformers, rotational isomers, and rotamers. Conformational isomerism is produced by rotation about the Single bond.
• Diastereomers
  These stereoisomers are non-image, non-identical. Diastereomers occur when the stereoisomers of a compound have differing configurations at corresponding stereocenters.^[15]
• Enantiomers
  Stereoisomers which are nonsuperimposable, mirror images.^[16]

Wikiquote has quotations related to Stereochemistry.

• Alkane stereochemistry
• Chiral resolution, which often involves crystallization
• Chirality (chemistry) (R/S, d/l)
• Chiral switch
• Skeletal formula#Stereochemistry which describes how stereochemistry is denoted in skeletal formulae.
• Solid-state chemistry
• VSEPR theory
• Nuclear Overhauser effect Describes a method in nuclear magnetic resonance spectroscopy (NMR) employed to elucidate the stereochemistry of organic molecules

References