192
6 Construction of the Names of Complex Compounds
reochemistry, obtain each for both enantiomers of the racemic pair (one
of two) under scrutiny.
C02H
HO-4-H
H+OH
Et
or
C02H
H+OH
HOT H
Et
(2R*,3S*)-2,3-Dihydroxypentanoic acid
threo-2,3-Dihydroxypentanoic acid
The following two dicarboxylic acids represent achiral diastereomeric
meso forms with a pseudostereogenic (formerly: pseudoasymmetric) Catom, C-5, which is given the descriptor r or s, respectively.
~H
~H
02N~C02H
02N·)~~Ac02H
(lR,3S,Sr)5-Nitrocyclohexane-1,3-dicarboxylic acid
Although for polycyclic systems too all stereogenic centers can be unambiguously characterized as shown above, for bicyclo[x.y.zlalkanes with
x ;::;: y> z > 0 a specific endol exo, synl anti formalism is generally preferred.
Thus, to a group pointing towards the bridge with the highest locants is
assigned the descriptor exo, if pointing away the descriptor endo; at the
same time a group located at that same bridge and pointing toward the
bridge with the lowest locants is characterized by the prefix syn, if pointing away by anti.
an~i syn
H 7 F
(CH2lz-1
~
1-(~H2)X-1
Br 5 4
C02H
(CH 2 );11 exo
1
2
endo
H
5-endo-Bromo-7 -syn-fluorobicyclo [2.2.1 1 heptane-2-exo-carboxylic acid
or: (lS,2R,4R,5S,7R)-5-Bromo-7- ...