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
cis trans naming system doesnts work when
carbon atoms have totally different groups attached
naming cis trans isomers
prefix cis- or trans-
