Inorganic Chemistry

1. CD & ORD SPECTROSCOPY
BOBBY SOLANKI
M.Sc. Chemistry
Sharda University
Greater Noida

2. OPTICAL ROTATORY DISPERSION
▪ It can be define as the rate of change of
specific rotation with change in wavelength.
▪ Measuring optical rotation as a function of
wavelength is termed optical rotatory dispersion
(ORD) spectroscopy.
▪ It can be measured by polarimeter.

3. FUNDAMENTALS OF ORD
▪ Plane polarized light.
▪ Optical activity.
▪ Specific rotation.
▪ Circular Birefringence.
▪ Optical Rotation.

4. PLANE POLARISED LIGHT
▪ Light from ordinary lamp consists of waves
vibrating in many different planes.
▪ When it is passed through polaroid's lens, it is
found to vibrate in one plane and is said to be
plane polarized light.

5. OPTICAL ACTIVITY
▪ The compounds which are having the ability to
rotate the plane of polarized light are called
optical active compounds.
▪ This property of compound is called optical
activity.
▪ It is measured by polarimeter.
▪ Compound which rotates of polarized light to
right (clock wise) is called DEXTROROTATORY &
is denoted by (+) sign.

6. ▪ If the compound rotates plane of polarized
light towards left side (anti clock wise) is called
LEVOROTATORY & is denoted by (-) sign.
▪ Enantiomers are optically active compounds.

7. For a compound to be optically active it must be
devoid of the following properties
1. Plane of symmetry
2. Center of symmetry
3. Alternating – axis of symmetry

8. SPECIFIC ROTATION
▪ It is defined as the rotation produced by a
solution of length 10cm and unit concentration
for given wavelength of light at the given
temperature.
▪ It is denoted by (a).

9. CIRCULAR BIREFRINGENCE
▪ If two equal & opposite beams of CPL & PPL
passes through an optically active compound it
result in characteristic phenomenon called
circular birefringence.

10. OPTICAL ROTATION
▪ When a plane polarized light (PPL) is passed
through optically active compound due to its
circular birefringence results in unequal rate of
propagation of left & right circularly polarized
rays.
▪ This unequal rate of propagation of both left &
right circularly polarized light deviates the PPL
from its original direction & it is called as
OPTICAL ROTATION.

11. CIRCULAR DICHROISM
• Some materials posses special properties of
absorption of the left circular polarized light to
different extent than the right circularly
polarized light.

12. • When the component emerges out there is an
imbalance in their strength & the resultant
two will not be linearly polarized but
elliptically polarized & this phenomenon is
called as CIRCULAR DICHROISM.

13. Cotton curves
▪ The combination of these two effects in the
region in which the optically active absorption
bands are observed gives rise to the
phenomenon called cotton effect and the curve
arises.

14. There are two types of cotton curves.
• 1. plane curve
• 2. anomalous curve
1.Plane curve:-
The curves obtained do not contain any peak
and curve do not cross the zero rotation line.
Such waves are obtained for compounds which
do not have absorption in the wavelength region
where optical activity is being examined.
Ex. hydrocarbons

15. 2. Anomalous curve:
These curve on the other hand shows a number of
extreme peaks and troughs depending on the
number of absorbing groups and therefore known
as anomalous dispersion of optical rotation.

16. ▪ This type of curve is obtained for compounds,
which contain an asymmetric carbon atom and
also contains chromophore.
▪ These are anomalous dispersion curves which
shows maximum and minimum both of them
occurring in the region of maximum absorption.
▪ approaching the region of cotton effect from
the long wavelength, one passes first trough
maximum(peak) and then a minimum (trough),
the cotton effect said to be positive. Positive
cotton effect is where the peak is at a

17. Higher wavelength than the trough.
▪ The opposite is called the negative cotton
effect.