School of Engineering and Science - Jacobs University

5. Restricted rotation giving rise to perpendicular dissymmetric planes. Some
compound what do not have asymmetric atoms are nevertheless chiral because
their structure could be represented as two perpendicular planes neither of
which can be bisected by a plane of symmetry (Fig. 1-5). There are few
examples for illustration below. Biphenyls containing four large groups can not
freely rotate about the central bond because of steric hindrance (Fig. 1-6). In
such compound the two rings are in perpendicular planes, that fits to the
structure in Fig. 1-5.
Fig. 1-5. Two perpendicular planes [3].
There are few examples for illustration below.
Cl
O 2 N
COOH
HOOC
NO 2
Cl
O 2 N
COOH
HOOC
NO 2
A
P(Ph) 2
P(Ph) 2
(Ph) 2 P
(Ph) 2 P
Mirror
Fig. 1-6. Chiral 3'-chloro-2',6'-dinitrobiphenyl-2,6-dicarboxylic acid (A) and binap (B)
[3].
6. Chirality due to a helical shape. Some molecules existing in helical shape with
left- or right-handed orientation (Fig. 1-7). The entire molecule is usually less
that one full turn of the helix, but this does not alter the possibility of left- and
right-handedness.
B
3