Controlling stereochemistry Flashcards
addition to completely symmetric molecule
homomeric products
C2 axis and mirror plane
addition to prochiral molecule
enantiomeric products
no C2 axis but mirror plane
addition to chiral molecule
diastereomeric products
no C2 axis or mirror plane
differentiating between homotopic compounds
can’t be differentiated
differentiating between enantiomeric compounds
use of enantiopure reagents/catalysts
produce enantioenriched product
differentiating between diastereotopic compounds
either by chiral or achiral reagents/catalysts
pros of chiral pool
cheap
good availability
sustainable
cons of chiral pool
structural restrictions
single enantiomer availability
strategies to separate enantiomers
- classical resolution - separation via selective crystallization
- chiral chromatography
- kinetic/dynamic kinetic resolution
chiral HPLC analysis
[high performance liquid chromatography]
stationary phase contains chiral selector that interacts differently with each enantiomer (silica)
then detected with UV/fluorescence/MS
chiral HPLC analysis - pros
cheap
common equipment
can be fully automated
chiral HPLC analysis - cons
uses sig. amount of solvent
can mask impurities
chiral columns = costly
3 agents used in NMR
chiral solvating agents (CSA)
chiral derivatizing agents (CDA)
chiral shift reagents (CSR)
anisotropic shielding
e- around nucleus generate local magnetic field which interacts with external magnetic field (B0)
opposes = shielding
addition = deshielding
