Chemistry Reference
In-Depth Information
NH
2
OH
CH
2
OH
CO
2
H
H
H
CO
2
H
CH
2
CO
2
H
(
−
)-serine
(+)-malic acid
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priorities
NH
2
CO
2
H
2
OH
H
priorities
OH
CO
2
H
2
CO
2
H
H
O
C
O
C
H
C
H
C
highest
atomic
number
lowest atomic
number
highest
atomic
number
lowest atomic
number
O
O
O
C
O
O
H
H
same atomic number;
next atom then considered,
both have oxygen;
carbonyl double bond
considered to be duplicated;
three oxygens > one oxygen
same atomic number;
next atom then considerd O > C;
carbonyl double bond considered
to be duplicated
view from this
side
view from
this side
priority 1
priority 1
priority 1
priority 1
NH
2
NH
2
OH
OH
priority 2
CH
2
OH
CO
2
H
H
H
priority 3
CO
2
H
CH
2
OH
CH
2
CO
2
H
HO
2
C
HO
2
CH
2
C
CO
2
H
priority 4
priority 4
priority 3
priority 2
priority 2
priority 3
priority 2
priority 3
anticlockwise:
S
clockwise:
R
nomenclature showing
optical activity and
configuration:
(
−
)-(
S
)-serine
(+)-(
R
)-malic acid
It is now possible to incorporate the configuration
of the compound into its nomenclature to give more
detail. (
−
)-Serine becomes (
−
)-(
S
)-serine, whilst (
+
)-
malic acid becomes (
+
)-(
R
)-malic acid. Because there
is no relationship between (
+
)/(
−
) and configuration
(
R
)/(
S
), it is necessary to quote both optical activity
and configuration to convey maximum information. The
descriptor (
RS
) is used to indicate a (
±
) racemic mixture
(see Section 3.4.1).
Note also that the configuration (
R
)or(
S
)isdefined
by the priority rules, and configuration (
R
) could easily
become (
S
) merely by altering one substituent. For
instance, all the amino acids found in proteins can be
represented by the formula
R
CO
2
H
α
-amino acids in proteins
H
NH
2
(−)-(
S
)-serine
priority 3
priority 2
CO
2
H
R = CH
2
OH
HO
R
CO
2
H
H
NH
2
(+)-(
S
)-alanine
CO
2
H
R = CH
3
NH
2
priority 1
H
NH
2
(+)-(
S
)-lysine
anticlockwise:
S
H
2
N
CO
2
H
R = (CH
2
)
4
NH
2
H
NH
2
priorities:
NH
2
> CO
2
H > alkyl > H
(−)-(
S
)-phenylalanine
CO
2
H
R = CH
2
Ph
H
NH
2
