PL - Optical isomers Flashcards
What are optical isomers/enantiomers?
Mirror images of each other and no matter which way you turn them, they can’t be superimposed.
What is a chiral (or asymmetric) carbon atom/centre?
One which has four different groups attached to it.
What are optical isomers also known as?
Enantioners.
If a molecule can be superimposed on its mirror image what is it?
Achiral - and it doesn’t have a chiral carbon.
What does it mean that optical isomers are optically active?
They rotate plane-polarised light.
One enantiomer rotates it in a clockwise direction, the other rotates it the same amount but in an anticlockwise direction.
What is the difference between the vibrations of normal light and plane-polarised light?
Normal light vibrates in all directions, but plane-polarised light only vibrates in one direction.
What do enantiomers do to plane-polarised light?
One enantiomer rotates it in a clockwise direction, the other rotates it the same amount but in an anticlockwise direction.
What are the enantiomers sometimes identified as?
The D isomer or the L isomer.
Are all naturally occuring amino acids D or L enantiomers?
L-amino acids.
Except glycine which isn’t chiral.
Are most sugars D or L enantiomers?
D-isomers.
How do you locate the chiral centre?
Look for the carbon atom with four different groups attached.
How do you draw optical isomers?
First locate the chiral centre by looking for the carbon atom with four different groups attached.
Then draw the isomers - draw one enantiomer in a tetrahedral shape (don’t try to draw the full structure of each group), then draw a mirror image.
What might a chiral centre be called instead?
A chiral carbon.
If a molecule has more than one chiral centre, what will be significant about its optical isomers?
It will have more than two optical isomers.
Why can there be a chiral centre on a ring?
Because although the carbon is attached to the same ring twice, the order of the atoms in the ring is different depending on which way round you go so they count as two different groups.
