Chapter 6 - Principles of Stereochemistry

Studying stereoisomers, which are compounds that have the same atomic connectivity but a different arrangement of atoms in space.

Absolute configuration

refers to the spatial arrangement of atoms in a chiral molecule, typically described using the Cahn-Ingold-Prelog priority rules to assign R or S configuration at each asymmetric carbon atom.

Chiral

molecules that have non-superimposable (aka different) mirror images, meaning they exist in two configurations that are mirror images of each other.

Chiral carbon atom

aka asymmetric carbon; a carbon atom that is bonded to four different groups.

Chiral center

the IUPAC term for an atom holding a set of ligands in a spatial arrangement that is not superimposable on its mirror image. asymmetric carbon atoms are the most common chirality centers.

Allene

compounds having two C=C double bonds that meet at a single carbon atom, C=C=C. the two outer carbon atoms are trigonal planar, with their planes perpendicular to each other. many substituted allenes are chiral!

Stereocenter

aka stereogenic atom; an atom that gives rise to stereoisomers when its groups are interchanged. asymmetric carbon atoms and double-bonded carbons in cis-trans alkenes are the most common stereocenters!!

Cis

on the same side of a ring or double bond.

Geometric isomers

aka cis-trans isomers; isomers that differ in their geometric arrangement on a ring or double bond; a subclass of diastereomers.

Stereoisomers

aka configurational isomers; isomers whose atoms are bonded together in the same order but differ in how the atoms are oriented in space.

Structural isomers

aka constitutional isomers; isomers that differ in the order in which their atoms are bonded together.

Conformational isomers

aka conformers; structures that differ only by rotations about single bonds. in most cases, conformers interconvert at room temperature; thus, they are not different compounds and not true isomers.

Diastereomers

stereoisomers that are not mirror images.

Enantiomers

a pair of nonsuperimposable mirror-image molecules: mirror-image isomers.

Isomers

different compounds with the same molecular formula.

Internal mirror plane (σ)

a plane of symmetry through the middle of a molecule, dividing the molecule into two mirror-image halves.

T/F: A molecule with an internal mirror plane of symmetry cannot be chiral.

TRUE

Dextrorotatory (+) or (d)

rotating the plane of polarized light clockwise.

Levorotatory (-) or (l)

rotating the plane of polarized light counterclockwise.

Mesocompound

an achiral (optically compound that contains chirality centers (usually asymmetric carbon atoms).