stereochemistry Flashcards
what is stereochemistry?
subdiscipline of chemistry that looks at the spacial arrangement of atom
what is important in drug action?
3D structure is important in drug action
what are isomers?
compounds have the same molecular formula
types of isomers?
constitutional or structural isomers
stereoisomers
what are stereoisomers?
compounds that are the same but have a different arrangement of space
what are conformation isomers?
different conformations of the same molecule
interconvert easily through rotation around single bond
what are configuration stereoisomers?
same groups are different in how they’re arranged around central carbon atoms
don’t interconvert easily so bond needs to be broken to interconvert
what is strain?
when stable molecule have weaker bonds than acyclic c-c bond and more unstable than propane
what are constitutional or structural isomers?
compounds with same molecular formula but different arrangement of atoms
what are the two types of newman projections?
eclipsed conformer high energy
staggered conformer low energy
what is the bond angle in angle strain?
60
what is the structure of torsional strain?
‘planar molecule
can’t do bond rotation
hydrogens are eclipsed’
structure of cyclobutane?
‘90 degrees angle
high ring strain
non-planar conformer minimizing eclipsing’
structure of cyclopentane?
‘angle 180 degrees
non-planar minimizing eclipsing
little ring strain’
structure of cyclohexane chair conformation?
angle 109.5 degrees if non-planar
no ring strain
no eclipsing in chair conformation
what are the hydrogens in cyclohexane arranged like?
either axial or equitorial
how are axial and equatorial relationship changed?
via ring flip of conformer
the conformers energy stays the same
how do you assign priority groups?
by looking at atomic number
(higher atomic mass for isotopes)
structure of cyclohexane boats?
no ring strain
eclipsed in boat conformation
in twist-boat the flagpole and eclipsed interactions reduced
both boat and twist-boat are higher energy than chair
what is tetrahedral carbon that can always be arranged in two ways called?
‘spatial sequence about a stereogenic centre’
what are enantiomers?
‘two molecules with opposite configurations at all centres’
what are R and S configurations?
R- clockwise rotation
S- anticlockwise
what are diasterioisomer?
‘stereoisomers that aren’t an enantiomer’
so don’t have opposite configurations at all centres
what are meso compounds?
groups around stereogenic centres that are symmetrical
when is a meso compound optically inactive?
when there’s a plane of symmetry
conformation vs configuration?
changing conformation doesn’t affect configuration
what is the (+)- or dextrorotatory enantomer?
plane rotates clockwise
and isomer is active
what is (–)- or laevorotatory enantiomer?
plane rotates anticlockwise
and isomer is inactive
what is the equimolar mixture?
racemate or racemic mixture
where the enantiomer is optically inactive (±)-
what are the physical properties of enantiomers and racemates?
between enantiomers the melting points are the same
racemates have different melting points
optical rotation is different in both
Pharmacological properties are different as well
what is the equation for specific rotation?
observed rotation/concentration (g/ml)* path length (dm)
example of a stereoisomer?
thalidomide:
one is an antidepressant and the other causes birth defects
