Organic 7: Stereochemistry Flashcards
Stereoisomers
isomers that have the same constitution but differ in the spatial arrangement of their atoms
Chiral
object not superimposable on its mirror image; a molecule is this if its 2 mirror-image forms are not superimposable in 3 dimensions
Achiral
a molecule that is superimposable on its mirror image
Enantiomers
stereoisomers that are related as an object and its nonsuperimposable mirror image; describes a particular relationship between 2 objects; a chiral molecule can have only one of these
Chirality center
an atom that has 4 nonequivalent atoms or groups attached to it; at various times, these have been called asymmetric centers or stereogenic centers
Plane of symmetry
bisects a molecule so that one half of the molecules is the mirror image of the other half
Center of symmetry
a point in the center of a molecule is this if any line drawn from it to some element of the structure will, when extended an equal distance in the opposite direction, encounter an identical element
Optical activity
ability of a chiral substance to rotate the plane of plane-polarized light
Polarimeter
instrument that measures optical activity
Racemic mixtures
mixtures containing equal quantities of enantiomers; optically inactive
Optically pure
at the limit, where all the molecules are of the same handedness
Enantiomeric excess
optical purity; percent of major enantiomer - percent of minor enantiomer
Specific rotation
effects of path length and concentration symbolized by alpha; a physical property; optical purity can be calculated [(___ of sample/___ of pure enantiomer) x 100]
Absolute configuration
the exact 3D spatial arrangement of substituents at a chirality center
Relative configurations
stereochemical configuration on a comparative, rather than an absolute, basis; terms such as D, L, erythro, threo, alpha, and beta describe relative configuration
Cahn-Ingold-Prelog System
AKA the sequence rules; system that deals with the problem of the absolute configuration at a chirality center
Fischer Projections
always generated the same way - the molecule is oriented so that the vertical bonds at the chirality center are directed away from you and the horizontal bonds point toward you; a projection onto the page is a cross; the chirality center lies at the center of the cross but is not explicitly shown
Prochiral
addition to either face converts an achiral reactant to a chiral product
Enantiotopic
product from reaction at 1 face is the enantiomer of the product from reaction at the other
Prochirality center
an atom of a molecule that becomes a chirality center when 1 of its attached atoms or groups is replaced by a different atom or group
Diastereomers
stereoisomers that are not mirror images; cis & trans isomers of a particular compound are ___ of each other
Erythro
when the carbon chain is vertical and like substituents are on the same side of the Fischer projection, the molecule is described as this type of diastereomer
Threo
when like substituents are on opposite sides of the Fischer projection, the molecules is described as this type of diastereomer
Meso forms
achiral molecules that have chirality centers
Conformational enantiomers
enantiomers interconvertible by a conformational change
Stereospecific reaction
reaction in which stereoisomeric starting materials yield products that are stereoisomers of each other
Diastereotopic
describing 2 atoms or groups in a molecule that are attached to the same atom but are in stereochemically different environments that are not mirror images of each other
Resolution
the separation of a racemic mixture into its enantiomeric components
Kinetic resolution
separation of enantiomers based on their unequal rates of reaction with a chiral reactant
Enzymatic resolution
resolution of a mixture of enantiomers based on the selective reaction of one of them under conditions of enzyme catalysis
