Chirality and stereochemistry Flashcards
What are isomers?
Compounds that have the same molecular formula but do not have identical structures
What are constitutional isomers?
Isomers that differ in the way their atoms are connected
e.g ethanol and dimethyl ether (C3H6O)
What are stereoisomers?
Isomers that have the same bonding order of atoms but differ in the way these atoms are arranged in space
What causes chirality in a molecule?
An asymmetric (stereogenic) centre, i.e a tetrahedral atom (carbon) with 4 different substituents
What are enantiomers?
Molecules that are non-superimposable mirror-images of each other
What are diastereomers?
Stereoisomers that are not mirror images
Enantiomers that rotate plane-polarised light clockwise are….
Dextrorotatory (+)
Enantiomers that rotate plane-polarised light anti-clockwise are…
Levorotatory (-)
+ and - enantiomers rotate plane-polarised light by the same _______ in different _________.
Angle (number of degrees is an achiral property)
directions (chiral property)
Is a racemic mixture optically active?
No, it is optically inactive: it does not produce a net rotation of polarised light
What are CIP rules used for?
To designate the absolute configuration of each chiral carbon in a molecule in terms of the arbitrary terms R (rectus) and S (sinister)
What are the true rules for assigning priority?
- Atoms directly attached to stereogenic centre are ranked by atomic number e.g.: Cl>O>C>H (Hint: if one atom is H, it necessarily has lowest priority)
- If decision cannot be reached under Rule 1, consider next the next atom in the chain
- Multiple bonds are treated as the equal number of single bonds (attach “dummy” atoms)
How is the absolute configuration determined after assigning priority?
- Look along axis from Carbon —> lowest priority substituent
- If MStar rotates clockwise: R
- If MStar rotates anticlokwise: S
