Optical Isomerism Flashcards
What do all optical isomers contain ?
chiral carbon atom
What type of isomerism are optical isomers ?
Stereoisomerism
What is a chiral carbon ?
carbon atom with four different atoms or groups bonded to it
Is the chiral carbon unsymmetrical ?
yes
What is the definition of Optical isomers ?
occur due to the presence of a chiral carbon, exist as a pair of non-superimposable mirror images and different in their effect on plane of polarised light
What is a racemic mixture ?
Contains equal amounts of each optical isomer
Explain how to draw optical isomers
identify the chiral centre and the four groups bonded to it
draw a tetrahedral shape around the chiral centre and fill in the four grouos
use a dotted line to represent the mirror, and draw the second isomer as the mirror image
Can CH3CH=CHCH3 exist as optical isomers. Why ?
no, there is no chiral carbon centre; can exist as E/Z isomers
What do optical isomers do in the presence of polarised light ?
rotate
What is plane polarised light ?
How is it achieved ?
light in which all waves vibrate in the same plane
using a polarising filter
If plane polarised light is shone on separate solutions of each enantiomer what will happen ?
one enantiomer will rotate the plane of polarised light to the left (prefix L)
The other enantiomer will rotate the plane of polarised light to the right (prefix D)
Explain why a racemic mixture will not caused the plane of polarised light to rotate
It rotates the light to the left and right equally
The sample is said to be optically inactive
Explain how you could distinguish between a racemate of lactic acid and one of enantiomers of lactic acid
plane polarised light will be rotated by the single enantiomer
but not by the racemate
because one enantiomer will rotate the light to the left and the other to the right by the same amount
