Separation of diasteromers by ir

2. Analysis of
Diastereomers by
IR Spectroscopy
Analysis of
Diastereomers
by IR Spectroscopy

3. Submitted to: Dr. Abida Ashraf
Submitted By:
Sidra MP-CHM-04
Maria Arshad MP-CHM-03
1st Semester
Stereochemistry CHM-533
Session 2020-2022
The Women University Multan

4. Diastereomers:
O Type of stereoisomers that are not mirror images
of each other and non identical isomers.
O They have plan of symmetry.
O Theses molecules have 2 or more stereo center.
O They are non superimposable.

5. Analysis/Separation of
diasteromers:
Recrystallization.
Diastereomers have
different
solubilities.
Column Chromatography.
Diastereomers have
different degrees of
attraction to a stationary
phase. ...
HPLC (High
Performance
Liquid
Chromatograph
y) ...
SCF
(Supercrit
ical Fluid
Chromato
graphy).
NMR
and IR
techniq
ues.

6. Analysis of
Diasteromers by IR-
Spectroscopy…
O Enantiomers are not differentiate by IR because they are
identical mirror image of others.
But,
O Diasteromers are easily analyzed by IR Spectroscopy or
NMR techniques due to difference in isomer structures.

7. IR-Spectra
IR spectra spectra
may be categorized
as :
“Well behaved”
group
frequencies,
“Shifty” bands
These two factors
are Useful for
determining the
presence of
functional group.
In general the
group frequency
comes from
stretching ,
bending
vibrational modes.
Most of IR bands
above 1600/cm
are well behaved.
The fingerprint
region below
1600/cm is a
mixture of well
behaved and shifty
bands.

8. In case of diastereomers:
O Diastereomers are isomers with two or more chiral
centers, differing only in configuration of one, but not
all, chiral centers.
O Theses are non identical mirror images compounds and
easily separated by IR Spectroscopy. Due to non
identical structure the arrangement of functional groups
or atoms each carbon show different peak at different
frequencies but some groups show similar frequency
peaks, that give us a clear image to separate the
different isomers.

9. Spectral differences show
up in some of the “shifty”
bands, and these
differences provide different
spectral fingerprint, which
are useful as standard to
differentiate the isomers.

10. Example:

11. Ephedrine and
Pseudo-ephedrine
O These are diastereomers, differing only in
the R/S configuration at the carbon holding
OH group.
Ephedrine
Pseudo ephedrine

14. O The blue arrows shown in previous slide
shows that these peaks are same in both
ephedrine and pseudo ephedrine spectrum.
O In fingerprint region three bands shown in
1100/cm region

15. • The O-H, N-H, and C-H stretch region of the
spectrum centered on 3000/cm .

16. Cocaine hydro chloride diastereomers:

18. O The only difference in peaks of these above
spectrum is due to arrangement of carbo-
methoxy group which is at axial position
cocaine hydro chloride and at equatorial
position of pseudo cocaine hydro chloride.
O The carbonyl peak shown in region 1700-
1900/cm.

19. Any Question?