CH25 Isomerism Flashcards
What property must a C have to display optical isomerism
4 different substituents attached to 1 C atom
Similarities between 2 optical isomers
Same atoms and bonds
Differences between 2 optical isomers
Differ in the way they rotate plane polarised light
Word used to describe optically active molecules
Chiral
What is a pair of isomers called
Enantiomers
What is a chiral centre
The carbon that has 4 different substituents attached to it
How is the chiral centre denoted
C*
How is light polarised
Passing it through a polaroid filter, so oscillations are only in one plane
What effect does the racemic mixture have on plane polarised light
None, as the rotation by each enantiomer cancels out to nothing
What effect does the + isomer have on plane polarised light
Rotates plane of polarisation by x degrees clockwise
What effect does the - isomer have on plane polarised light
Rotates plane of polarisation by x degrees anti-clockwise
What is the structure of a polarimeter
Light source –> polarising filter –> polarised light
passes through compartment with sample–> Detector determines angle of rotation of the plane of polarised light
What are polarimeters used for
To identify which enantiomer is present, the purity of the sample, the conc of the sample
First stage of synthesis of lactic acid
CH3CHO + HCN –> CH3CH(OH)CN
Why is CH3CH(OH)CN molecule chiral
Has H, CH3, OH and CN groups attached to it
