[PHA6113 lab] Activity 5: Optical Activity Flashcards
Property of substances to rotate the plane of polarization to the polarized light
Optical Activity
What USP number is Optical Activity?
<781>
[Characteristics]
T or F: Molecules should be superimposable
False, should not be superimposable (disymmetric)
[Characteristics]
T or F: There should be a presence of a chiral carbon
True
A carbon that has 4 different molecules attached to it
Chiral carbon
What do you call the rotation for liquids?
Optical rotation
What do you call the rotation for solids or substances in a solution?
Specific rotation
What instrument is used for taking optical activity?
Polarimeter
Different types of Polarimeter
Visual and Photoelectric
General parts of a Polarimeter
Light source, Polarizer, Analyzer
This holds the sample inside a polarimeter
Sample tube or Polarimeter tube
<781A>
Determination of Angular Rotation
Symbol used for Angular Rotation
a (alpha)
The optical rotation of the neat liquid is measured in a ___________
1.0-dm tube at 589nm at 25 degrees (unless otherwise stated)
Laboratory Procedure for Determination of Angular Rotation
> Turn on light source
Rotate analyzer until tripartite field becomes equal in intensity
Rinse the polarimeter tube with distilled water then fill to the top (overflow)
Tighten the screw caps carefully - not too tight and not too loose to prevent double refraction under pressure
Place the tube in the polarimeter and rotate the analyzer until the field is equally illuminated – Make 1 reading of this blank
[Interpretation]
Dextrorotatory
(+) - clockwise
[Interpretation]
Levorotatory
(-) - counterclockwise
When there is an equal portion of both levo and dextro, what is it called?
Racemic Mixture
REMEMBER
Do readings clockwise
Do readings counterclockwise
Compare and the lesser one will be used
HOW TO READ A POLARIMETER
PRACTICE READINGS FROM THE PPT
[Determination of Angular Rotation]
What is the general equation?
a solute = a solution - a solvent
[Determination of Angular Rotation]
When there are different signs, what is the rule?
Add then take the sign of the larger value
[Determination of Angular Rotation]
When there are same signs, what is the rule?
Subtract and copy the sign
Angle through which the plane of polarization of light is rotated when polarized light passes through a 1dm layer of the liquid at a specified temperature
Specific Rotation
<781S>
Specific Rotation
Symbol for Specific Rotation
[a]^t_y
T or F: Measurements for Specific rotation is the same with optical rotation
True –> 1.0-dm tube at 589nm at 25 degrees
Formula for Specific or Optical Rotation
[a]^t_y = a/lc
where; a - angular rotation
l - length of the tube
c - concentration (solids or solutions); density (liquids)
Rotation of plane polarized light occurs at a ____________, so the extent of the rotation is ___________ to the amount of optically active material
Molecular level, proportional
[Determination of Molar Rotation]
Formula of Molar Rotation
[o] = ([a]^t_y x MW) / 100
PRACTICE PROBLEMS
PRACTICE USING PPT
