Isomerism and Stereochemistry Flashcards
Stereochemistry: chemistry of molecules in 3D
Organic molecules
> structural isomers + stereoisomers
> conformational + configurational
> optical + geometrical
Structural isomers
same molecular formula
atoms bonded in different orders
Different properties
Conformational
rotation around σ bonds and 3D shape of sp3 centre
Stereoisomers
same molecular formula
atoms bonded in same order
different 3D arrangement
Configurational
No conversion by rotation of single bond
Geometrical
cis/trans
E/Z
stereoisomers that arise due to restricted rotation
within a molecule
Optical
D/L
S/R
how many structural isomers?
7
Montelukast:
Symptomatic relief of seasonal allergic rhinitis in patients with asthma and prophylaxis of asthma in children (note: oral formulation)
conformational isomers (CI)
configurational isomers: optical isomers (OI)
configurational isomers: geometrical isomers (GI)
tetrahedral angle, degree?
109.5 degree
All single bonds are ____to rotate
Although might be restricted by nearby ______ groups
free
bulky
cis
same side
trans
opposite side
highest priority?
biggest atomic number
geometric can happen only when…
two different groups at each end of double bond
use E/Z for when…
you have multiple functional groups and there are different priorities dependent on the Ar
carbon has _____ priority than hygrogen
higher
e.g. 1-bromo-1-chloro-2-methylbut-1-ene:
search diagram
Bromine is higher priority than chlorine
1. Carbon is same priority as carbon
2. Carbon is higher priority than hydrogen
For linear carbon chains, the longest one is always highest priority
double bond - rotation?
cannot rotate
when c attached to 4 diff groups;
When a carbon is attached to 4 different groups/ arms present, none of which are the same
Configurational Isomers: chirality
think of left and right hand…
cannot be superimposed
What is the Achiral carbon?
At least 2 same groups/atoms present
Yes plan of symmetry
compound and its mirror image are the same, can be superimposed
Define Enantiomers:
Same physical/chemical properties
Differ in activities with plan polarised light that gives rise to optical isomerism, and also in their pharmacological actions
non-superimposable
Chiral centre
the C in the middle functional groups attaches to it
Chiral molecules ______ plane-polarised light: this is called ______ activity
rotate
optical
Racemic Mixture
A mixture that contains more of one enantiomer than the other is optically active
rotation - naming:
clockwise / anti-clockwise
Rotation clockwise direction: dextrorotatory, (+)
Anticlockwise rotation: levorotatory, (−)
Examples of drugs that are racemic mixtures
atenolol
warfarin
Configurational Isomers: D and L system are…
Fisher: (+)-glyceraldehyde enantiomer=D-glyceraldehyde,
(-)-glyceraldehyde enantiomer=L-glyceraldehyde
How to assign R & S system?
1) Priority: from 1 to 4 = assigned on basis of atomic number.
Higher atomic number gets higher priority
2) Substituents: if no priority, the next set of atoms in the unassigned groups is examined
3) Double or triple bonds: assigned priorities as if both atoms were duplicated or triplicated
4) Arrange (rotate) the molecule: group 4 is pointing away from the viewer
learn the different lines
thick black - pointing towards you
faint lines - pointing away from you
Lowest-priority group always pointing ____ from us
away
Each additional chiral centre generates ________ isomers
additional
Labetalol
a member of the beta-blocker family (drugs that bind to beta-adrenergic receptors). It is used to treat hypertension, especially hypertension in pregnancy
