3. Introduction
• ORD refers to the change in optical rotation with
the change in wavelength of light source. i.e.
applied only in optically active compounds.
• Optical rotation caused by compound changed with
wavelength of light was first noted by Biot in
1817.
• ORD curves in recent years are made use in
structural determination by comparing the curve
obtain from compound believed to have related
structures particularly applied to carbonyl
compounds.
4. Natural Light
o Natural light is having two components electric
component and magnetic component, and both are
perpendicular to each other in different planes.
o Both these electric component and magnetic
components are also perpendicular to the direction
of propagation of light.
6. Optical activity
Ability to rotate plane of polarized light
Optically active compound :-
• The compounds which are having the
ability to
rotate the plane of polarised light are
called optically active compounds.
• This property of compound is called
optical Activity.
7. •It is measured by Polarimeter.
• Compound which rotates plane of polarised light
to right (clock wise) is called DEXTROROTATORY
& is denoted by (+) sign.
•If the compound rotates plane of polarised light
towards left side (anti clock wise) is called
LEVOROTATORY & is denoted by (-) sign.
8. • Optical activity is not seen in symmetrical molecules
due to equal rotation in opposite directions getting
cancelled. The isomer that rotates the plane of
polarization to the left is called levo isomer (-) and
to the right is called dextro isomer (+).
• To be optically active , a molecule must not
possessed any one of following symmetry elements:
1) Centre of symmetry
2) Plane of symmetry
3) An Proper axis
9. Optical Rotatory Dispersion
The specific rotation [α] changes
with wavelength is called optical
rotatory dispersion (ORD) .
Or
The rate of change of specific rotation
with wavelengt
10. Drude has shown that the specific rotation
may be expressed as a function of wavelength
by an equation,
[α] =
where
λ- Wavelength of measurement
k1,k2 ,k3 – constants that can be identified with the
wavelength of maximum absorption of optically active
absorption bands
13. From graph,
A-Represents the plain positive ORD curve :
The specific Rotation increases with decreasing
wavelength.
B – Represents the plain negative ORD curve :
Plain – implies that there exist no maximum or
minima in the curve
14. • Chetwal GR & Anand SK, Instrumental method of chemical
analysis, 5TH edition page no:- 2.468- 2.481.
• Kalsi PS, Spectroscopy Of Organic Compounds, New age
international limited, sixth edition:611- 627.
• Jag Mohan, Organic Spectroscopy Principles And
Applications, Narosa publishing hose:482- 496.
• Sharma BK, Instrumental method of chemical analysis,
26TH edition:-M-286 to M-307.
References
