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Transcript of Isomerism
Stereoisomers are subdivided into two classes—conformational isomers, which
interconvert by rotation about a σ bond and configurational isomers that
interconvert only by breaking and reforming a bond.
To know the types of isomerism that exist
To be able to demonstrate this in practical form
Cis-trans isomers can occur in alkenes or cycloalkanes (or heteroanalogues) and differ in the positions of atoms (or groups) relative to a reference plane. According to IUPAC, E/Z isomers refer to alkenes of the form R1R2C=CR3R4 (R1 ≠ R2, R3 ≠ R4) where neither R1 nor R2 need be different from R3 or R4. •
A chiral carbon is a carbon joined to four different atoms or groups. • An optically active compound can rotate the plane of polarized light as it passes through a solution of the compound.
Optical isomers are enantiomers. Enantiomers are non-superimposeable mirror images of each other.
Diastereomers are not mirror images of each other.
A racemic mixture (or racemate) is a mixture of two enantiomers in equal amounts and is optically inactive.
There are two forms of eniantomer, D and L depending on whether the rotate the plane of polarised light right (D) or left (L) when it passes through it. This test is called POLARIMETRY and a 50:50 mixture of D and L forms will not affect the light.
Configurational isomers are further subdivided into cis-trans and E/Z isomers and optical isomers.
Rules for determining priorities
These are known as Cahn-Ingold-Prelog (CIP) rules after the people who developed the system.
What are they?
Physical and chemical properties of Cis/Trans & E/Z Isomers
No chemical differences
Physical differences because of different intermolecular and intramolecular interactions
Cis/trans ethene dicarboxylic acid
Polarimeters measure the optical actvity of eniantomers.
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