Stereochemical
absolute
Nomenclature
stereochemistry:
• R / S
denotes absolute stereochemistry for stereogenic atoms
H
Cl
Cl
OH
H
OH
(1S,2R)-2-chloro-1-cyclohexanol
• + / -
refers to optical rotation. Does not correlate to absolute configuration.
(+)
refers to those molecules that rotate plane polarized light in a clockwise
direction
( - )
refers to those molecules that rotate plane polarized light in a counterclockwise
direction
H
N
H CH 3
HO 2 C
CH 3
N
H H
CO 2 H
(R)-(+)-methylsuccinic acid
relative
(R)-(-)-2-methylpiperidine
stereochemistry:
• R* / S*
denotes relative stereochemistry for stereogenic atoms in racemic systems with more
than one stereocenter (less frequently used)
Cl
Cl
OH
OH
or
(1S*,2R*)-2-chloro-1-cyclohexanol
• cis / trans
describes relationship between two substituents in cyclic systems and in simple alkenes
OH
OH
CH 3
CH 3
CH 3
CH 3
H
cis
trans
H
cis
H
CH 3
CH 3
H
trans
• E / Z
describes stereochemistry of alkenes (simple and more complex)
CH 3
H
CH 3
H
CH 3
H
Z
• syn / anti
Cl
CH 3
CH 3
CH 3
H
H
Cl
H
Z
E
CH 3
OCH 3
E
describes relationship between two substituents in an acyclic system (longest chain on
zig zag)
CH 3
CH 3
OH
OH
OH
OH
syn
anti
• erythro/ threo
CH 3 CH 3
CO 2 M e
OH
2,3-anti; 3,4-syn; 2,4-anti
traditional terminology used to describe relationship between two substituents on
an acyclic molecule. Originally designed for glycols. With other systems gets
confusing (= do not use except for glycols).
HO
OH
HO
H
H
H
R
R
erythro
OH
R
R
H
threo