To assign the relative stereochemistry as l or u, the
first step is to assign the absolute configuration at each stereocentre
as R or S. For compounds 4.1-4.4, these are given
in Table 4.1. For compound 4.1, both stereocentres have the
same absolute configuration (S), so this the l-diastereomer.
Similarly, for compound 4.2, both stereocentres have the same absolute
configuration (R), so this the l-diastereomer. For compound
4.3, the two stereocentres have different absolute configurations
(one R and one S), so this is the u-diastereomer.
Similarly, for compound 4.4, the two stereocentres have different
absolute configurations (one R and one S), so
this is the u-diastereomer.
To assign the relative stereochemistry using the syn / anti
nomenclature, the compounds must be drawn in flying wedge projections which
requires rotation around the C2-C3 bond as shown below. For compound 4.1,
the two non-hydrogen substituents (the amino and hydroxyl groups shown
in red below) are on opposite sides of the carbon chain, so this is the
anti-diastereomer. Similarly, for compound 4.2, the two non-hydrogen
substituents are on opposite sides of the carbon chain, so this is the
anti-diastereomer. For compound 4.3, the two non-hydrogen
substituents are on the same side of the carbon chain, so this is the syn-diastereomer.
Similarly, for compound 4.4, the two non-hydrogen substituents are
on the same side of the carbon chain, so this is the syn-diastereomer.
To assign the relative stereochemistry as l or u, the first step is to assign the absolute configuration at each stereocentre as R or S. For compounds 4.5-4.7, these are given in Table 4.2. For compound 4.5, both stereocentres have the same absolute configuration (R), so this the l-diastereomer. Similarly, for compound 4.6, both stereocentres have the same absolute configuration (S), so this the l-diastereomer. For compound 4.7, the two stereocentres have different absolute configurations (one R and one S), so this is the u-diastereomer.
To assign the relative stereochemistry using the syn / anti nomenclature, the compounds must be drawn in flying wedge projections which requires rotation around the C2-C3 bond as shown below. For compound 4.5, the two non-hydrogen substituents (the two bromine atoms shown in red below) are on the same side of the carbon chain, so this is the syn-diastereomer. Similarly, for compound 4.6, the two non-hydrogen substituents are on the same side of the carbon chain, so this is the syn-diastereomer. For compound 4.7, the two non-hydrogen substituents are on opposite sides of the carbon chain, so this is the anti-diastereomer. Note that comparison of the answers to parts 4.1-4.4 with those to 4.5-4.7 shows that there is no correlation between the l / u and syn / anti nomenclatures.
To assign the relative stereochemistry as l or u, the
first step is to assign the absolute configuration at each stereocentre
as R or S. For compounds 4.10 and 4.12-4.14,
these are given in Table 4.3. For compound 4.10, the stereocentres
at C2 and C3 have the same absolute configuration (R and r),
whilst the stereocentres at C3 and C4 have opposite absolute configurations
(r and S). Hence, this is the lu-diastereomer. Note,
that the first stereochemical descriptor corresponds to the relative stereochemistry
of the two lowest numbered stereocentres. For compound 4.12, there
are only two stereocentres (C2 and C4) and these both have the same absolute
configuration (R), so this the l-diastereomer. Similarly,
for compound 4.13, there are only two stereocentres (C2 and C4)
and these both have the same absolute configuration (S), so this
the l-diastereomer. For compound 4.14, the stereocentres
at C2 and C3 have opposite absolute configurations (R and s),
whilst the stereocentres at C3 and C4 have the same absolute configuration
(s and S). Hence, this is the ul-diastereomer.
To assign the relative stereochemistry using the syn / anti
nomenclature, the compounds must be drawn in flying wedge projections
as shown below. The non-hydrogen substituent attached to the lowest numbered
stereocentre (C2) is then used as a reference to determine the relative
stereochemistry. The reference substituent is shown in red in the diagrams
below. For compound 4.10, the non-hydrogen substituent attached
to C3 is on the opposite face of the molecule as the reference substituent
on C2, whilst the non-hydrogen substituent on C4 is on the same face as
the reference substituent on C2. Hence, this is the anti-syn diastereomer.
For compound 4.12, the non-hydrogen substituent attached to C3 is
on the opposite face of the molecule as the reference substituent on C2,
as is the non-hydrogen substituent on C4. Hence, this is the anti-anti
diastereomer. Similarly, for compound 4.13, the non-hydrogen substituent
attached to C3 is on the opposite face of the molecule as the reference
substituent on C2, as is the non-hydrogen substituent on C4. Hence, this
is the anti-anti diastereomer. For compound 4.14, the non-hydrogen
substituent attached to C3 is on the same face of the molecule as the reference
substituent on C2, as is the non-hydrogen substituent on C4. Hence, this
is the syn-syn diastereomer.
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