Introduction To Stereochemistry Flashcards
Conformation=
Different arrangements caused by rotations alone
Conformers
Different conformations which are energy minima
Karplus equation
Determines size of coupling constant between 2 protons
-varies with dihedral angle
Constitutional/structural isomers
Different connectivity between atoms
Configurational isomers (stereoisomers)
All have same constitution but structures have different shape and can’t be inter-converted by rotating single bonds
If stereoisomers are non-superimposable mirror images=
Enantiomers
If stereoisomers aren’t enantiomers=
Diastereomers
Properties of enantiomers
Same chemical and physical properties
Properties of diastereomers
Properties aren’t the same
Non-optically active diastereomer=
Meso form
If there are 2 stereogenic centres
Have two sets of enantiomers
The sets are diastereomers of each other
Chiral if:
- no symmetry
- only rotational symmetry
Achiral if:
- plane of symmetry
- centre of inversion
- improper rotation axis (rotate then reflect)
Achiral molecules
Can be superimposed onto their mirror image
How to resolve enantiomers
1) Add enantiomerically pure amine
- > diastereomeric salts (different properties)
2) dissolve in ethanol (one dissolves, the other does not)
3) filter
- >seperate
Diastereotopic protons
If compare molecule where Ha is replaced with D with one where Hb is replaced with D, they are diastereomers
- never in exactly the same environment
- are strongly coupled to each other
Energy of alkenes
More substituted= lower in energy
Elimination tends to be
Antiperiplanar
A-value
A group’s preference for an equatorial position
Trans decalin
Locks ring conformation
3J (ax-ax)
9-13Hz
3J (eq-eq)
1.5-6.5Hz
3J (ax-eq)
1.5-6.5Hz
2J (geminal)
11-14Hz
