13.2 Stereoisomers

define stereoisomers

compounds that have the same structural formula but a different arrangement of the atoms in space

in what compounds does E/Z isomerism occur

compounds with a c=c double bond

in which compounds does optical isomerism occur

alkanes without functional groups

chiral molecules

why does stereoisomerism occur around double bonds

rotation around the double bond is restricted

so the groups attached to each carbon are fixed relative to each other

because of the position of the pi bonds electron density above and below the plane of the sigma bond

conditions for a compound to have E/Z isomerism

1) has c=c double bond 2) has different groups attached to each carbon atom of the double bond

define cis-trans isomerism

example of E/Z isomerism where one of the attached groups on each carbon atom of the double bond must be hydrogen

cis

hydrogen atoms on each carbon in the double bond on the same side of the molecule

trans

the hydrogen atoms on each carbon atom in the double bond are diagonally opposite each other

describe Cahn-Ingold-Prelog rules

1) higher the atomic number = higher the priority

2) if the groups of higher priority are in the same side of the double bond the compound is the Z isomer

3) if the groups of higher priority are diagonally placed across the double bond the compound is the E isomer