Res. Chem. Intermed.
, Vol. 28, No. 1, pp. 25 –28 (2002)
The absolute orientation of a molecule in space:
Extension of the ‘CIP’ system
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
Received 23 July 2001; accepted 29 October 2001
Abstract—A scheme for denoting the absolute spatial orientation of molecules and molecular
fragments is presented; this is based on three angular deviations — one for each spatial dimension
— with respect to a reference orientation, which is itself de ned with the help of certain features of
the Cahn – Ingold–Prelog stereochemical notation. The new scheme helps in reconstructing the three-
dimensional characteristicsof molecules from purely verbal descriptors, and may thus nd application
in various information storage and retrieval processes (e.g. encrypting holograms, etc.).
: Absolute; orientation; space; ‘CIP’; Cahn – Ingold– Prelog.
The verbal representation of the stereochemical features and relationships of mole-
cules has been an important preoccupation during the evolution of stereochemistry.
Such representations reduce and simplify the complex two- and three-dimensional
characteristics of whole molecules and their fragments into verbally stated descrip-
tions — invaluable for the purposes of verbal discussion and argument, not to men-
tion the abstracting of information in a concise format. Classical organic stere-
ochemistry employed the ‘L’ and ‘D’ nomenclature with reference to the enan-
tiomeric glyceraldehydes, which had to give way to the rigorous, elegant and versa-
tile Cahn – Ingold– Prelog (‘CIP’) system currently in use for denoting enantiomeric
relationships . (Diastereomeric relationships are ususally denoted by the ‘
or ‘threo-erythro’ nomenclatures.)
All the above systems, however, are concerned with denoting the geometry around
chiral atomic centres — whether absolute or relative. Interestingly, there exists no
system for representing the orientation of a molecule per se in space with respect to
an observer. In fact, one may envisage several uses for such a system, e.g. denoting
the mutual orientation either of two interacting molecules (say, a transition state or a