5. stereoisomerism Flashcards
carbon atoms in a C=C bond are what shape?
what is the bond angle
triganol planar
120
why cant atoms rotate around a C=C bond
due to the way the p orbitals overlap to form a pi bond
what causes alkenes to form stereoisomers
the restricted rotation around the C=C bond
what are stereoisomers
molecules with same structural formula but a different arrangement in space
types of stereoisomerism
e/z isomerism
Z isomer has
both groups attached above or below double bond
E isomers have
same groups positioned across double bond
E-but-2-ene
CH3…CH3
C=C
H…H
Z-but-2-ene
CH3…H
C=C
H…CH3
Chan-Inglod-Prelog (CIP rules) allow you to
work out E/Z isomerism when all groups are different
how CIP rules work
the atom with the higher atomic number one each C is given the higher priority (1)
if the priority groups (1) are positioned across from eachother it is a E isomer
if priority groups are postitioned both above or below the double bond it is a Z isomer
when working out priorities of groups attached to CS
take into account what the groups are attached to aswell
e.g. CH3 vs CH2CH3. CH2CH3 is priority (1) group
E/Z isomers can sometimes be called
Cis/Trans isomers
Cis isomers
groups are on the same side of the double bond
trans isomers
groups are on opposite sides of double bond
