Cahn-Ingold-Prelog Descriptors of Absolute Configuration for Carbon Cages

Abstract

A simplified procedure is described for assigning Cahn-Ingold-Prelog descriptors to stereocentres in spheroalkanes (the CnHn molecules, with n even, based on trivalent, polyhedral carbon frameworks, a class which subsumes the fulleranes). By extension, similar descriptors can be found for the atoms of fullerenes and related carbon-only molecules. Assignment maps are given for chiral fullerenes C28 C76, C78, C84 and C140, and for a number of spheroalkanes. Cases of breakdown of the simple procedure for triangle-rich spheroalkane molecular graphs are discussed.

Applications and properties of the Bijvoet intensity ratio

“…For these latter cases, it may be that Ex is too large and has to be reduced to take account of the presence of a centrosymmetric substructure. We have not pursued this analysis further in view of the known difficulties of establishing any valid quantitative measure of pseudo-symmetry (see for example Collins et al, 2006;Rassat & Fowler, 2004;Spek, 2003). For the other structures, there is no indication of a centrosymmetric substructure by checkCIF/PLATON.…”

23 Fullerenes

“…21 A procedure for assigning Cahn-Ingold-Prelog descriptors to stereocentres in spheroalkanes, the fully hydrogenated form of a trivalent, polyhedral carbon framework, a class of molecules which includes the fullerenes, has been developed. 22 The predicted nucleus-independent chemical shifts (NICS) of BN-doped fullerenes show that these species are more aromatic than [60]fullerene. 23 Semiempirical AM1 and MNDO methods have been used to examine the relative stabilities of several isomers of BN substituted fullerenes of the general formula C 60 Ϫ 2x (BN) x .…”

Topological Rotational Strengths as Chirality Descriptors for Fullerenes

“…However, it is precisely related through a well defined flattening process to a two‐dimensional object, the Schlegel diagram. A practical way1a,1b,1d, 3 of obtaining this diagram is to place a ball‐and‐stick molecular model on a plane and to flatten the whole object into the plane so that the bottom face expands to contain the rest. This flattening procedure corresponds to one of several definitions for Schlegel diagrams,20 and the choice of top and bottom faces is in principle arbitrary although standard conventions are available for fullerenes 1a,1b…”

“…For 6, 7 and 9 the standard IUPAC numbering scheme1a,1b is used to label the Schlegel diagram, and for 1 – 5 and 10 the labelling is taken from ref. 3. For 10 , only a small central portion of the Schlegel diagram is shown (for the full version of the diagram of the opposite enantiomer, see ref.…”

“…Different systems for the assignment of absolute configuration to fullerenes have been proposed, each requiring a standard numbering scheme 1. Extension of the Cahn–Ingold–Prelog rules2 to bare carbon cages3 allows assignment of an R or S descriptor to each carbon, and if a convention for labelling a specific carbon were added, could give a molecular descriptor by taking the descriptor of this carbon for the fullerene as a whole. However, it seems desirable to have a simpler procedure that is easy, automatic to apply and is based on purely graph‐theoretical considerations.…”