The two isomers are shown in the diagram above, and can be classified
using either the cis / trans or the E / Z nomenclature
system. The cis-isomer is the isomer in which the two hydrogen atoms
are on the same side of the alkene, whilst the trans-isomer is the
isomer in which the two hydrogen atoms are on opposite sides of the alkene.
To classify the two isomers using the E / Z nomenclature,
the atoms directly attached to each end of the alkene are compared. There
is a hydrogen atom and a carbon atom attached to the left carbon of the
alkene bond, these are shown in red in the diagram above. Using rule 1
of the CIP rules, the atom of higher atomic number has the higher precedence,
so C > H. Similarly, there is also a hydrogen atom and a carbon atom
attached to the right carbon of the alkene bond, these are shown in
blue in the diagram above. Using rule 1 of the CIP rules, the atom of higher
atomic number has the higher precedence, so again C > H. In the cis-isomer
of the alkene, the groups on the left and right side of the alkene which
have the highest precedence (the red and blue carbon atoms) are on the
same side of the alkene, so this is the Z-isomer, whilst for the
trans isomer of the alkene, the two groups which have highest precedence
are on opposite sides of the alkene so this is the E-isomer.
The two isomers (A and B) are shown in the diagram above, and can be
classified using the E / Z nomenclature system. Note that
the cis / trans nomenclature can only be used for disubstituted
alkenes and so is not appropriate in this case. To classify the two isomers
using the E / Z nomenclature, the atoms directly attached
to each end of the alkene are compared. For the substituents attached to
the carbon atom at the right end of the alkene, the situation is exactly
as in part a), so the carbon of the methyl group has precedence. The two
substituents attached to the left carbon of the alkene bond both start
with a carbon atom shown in red in the diagram above. Hence, the precedence
of the groups cannot be determined from rule 1 of the CIP rules. Therefore,
rule 2 is invoked and the next atoms along each substituent are examined.
For the ethyl group these are a carbon and two hydrogen atoms (shown in
blue), whilst for the methyl group only three hydrogen atoms (also shown
in blue) are present. The blue atoms in each chain are then compared, starting
with the atoms of highest atomic number. These are C and H, and using rule
1 C > H so the ethyl group has a higher priority than the methyl group.
Hence, in isomer A the groups on the left and right side of the alkene
which have the highest precedence are on the same side of the alkene, so
this is the Z-isomer. For isomer B, the two groups which have
highest precedence are on opposite sides of the alkene so this is the
E-isomer.
The two isomers (A and B) are shown in the diagram above, and can be
classified using the E / Z nomenclature system. To classify
the two isomers using the E / Z nomenclature, the atoms directly attached
to each end of the alkene are compared. In both cases, the atoms of an
ethyl and methyl group are to be compared, and the procedure is exactly
as described in part b). Hence, in isomer A the groups on the left and
right side of the alkene which have the highest precedence are on the same
side of the alkene, so this is the Z-isomer. For isomer B, the two
groups which have highest precedence are on opposite sides of the alkene
so this is the E-isomer.
The two isomers are shown in the diagram above, and can be classified
using either the cis / trans or the E / Z nomenclature
system. The cis-isomer is the compound in which the two non-hydrogen
atoms attached to the C=N are on the same face of the imine bond, whilst
the trans-isomer is the compound in which the two non-hydrogen atoms
are on opposite faces of the double bond. To classify the two isomers using
the E / Z nomenclature, the atoms directly attached to each
end of the C=N are compared. In the case of the carbon end of the double
bond, these are a carbon and a hydrogen atom, and the carbon atom has precedence
(rule 1). In the case of the substituents attached to the nitrogen atom,
the oxygen atom is compared with the lone pair of
electrons. Rule 4 states that a lone pair always has the lowest precedence,
so the oxygen atom has the higher precedence. Hence, in the cis-isomer
the groups on the left and right end of the imine which have the highest
precedence are on the same side of the alkene, so this is the Z-isomer.
For the trans-isomer, the two groups which have highest precedence are
on opposite sides of the imine so this is the E-isomer.
The two isomers (A and B) are shown in the diagram above, and can be
classified using the E / Z nomenclature system. To classify
the two isomers using the E / Z nomenclature, the atoms directly
attached to each end of the C=N are compared. In the case of the carbon
end of the double bond, these are both carbon atoms (shown in red), so
rule 2 is invoked and the next atoms along the chains are compared. In
both case, these are a carbon and two hydrogen atoms (shown in blue), so
it is necessary to examine the next atoms along the chain. Once again,
in both cases the atoms are a carbon atom and two hydrogen atoms (shown
in magenta) so it is necessary to look still further along the chain. At
the next level however, a difference is found since in the propyl substituent
the next three atoms are all hydrogens (shown in green), whilst in the
butyl substituent the atoms are a carbon and two hydrogens (shown in green).
Comparing the green atoms of highest atomic number gives C > H, so the
butyl substituent has a higher priority than the propyl group. In the case
of the substituents attached to the nitrogen atom, the carbon atom is compared
with the lone pair of electrons. Rule 4 states that a lone pair always
has the lowest precedence, so the carbon atom has the higher precedence.
Hence, in isomer A the groups on the left and right end of the imine which
have the highest precedence are on the same side of the alkene, so this
is the Z-isomer. For isomer B, the two groups which have highest
precedence are on opposite sides of the imine so this is the E-isomer.
The two isomers are shown in the diagram above, and can be classified
using either the cis / trans or the E / Z nomenclature
system. The cis-isomer is the compound in which the two chlorine
atoms are on the same face of the N=N double bond, whilst the trans-isomer
is the isomer in which the chlorine atoms are on opposite faces of the
N-=N bond. To classify the two isomers using the E / Z nomenclature,
the atoms directly attached to each end of the N=N are compared, and in
both cases these are a chlorine atom and a lone pair of electrons. Rule
4 states that a lone pair always has the lowest precedence, so the chlorine
atom has the higher precedence. Hence, in the cis-isomer the groups
on the left and right end of N=N which have the highest precedence are
on the same side of the alkene, so this is the Z-isomer. For the
trans-isomer, the two groups which have highest precedence are on
opposite sides of the N=N so this is the E-isomer.
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