A combined theoretical and experimental approach is used to recognize
the sterochemical patterns which emerge when X(2) (X=H, halogen, etc.)
is added to C-60 to form C(60)X(n), and the patterns formed by rings
which incorporate carbon atoms of the fullerene, C-60(ring)(n). Additi
on to form C(60)X(2) occurs either at an edge linking two hexagonal fa
ces on C-60, or across the para-positions of one of the hexagonal face
s. Further addition occurs to produce potentially a very great number
of isomers, but in some cases at least the pattern emerging is relativ
ely simple. An important feature is the tendency of hexagonal faces wi
th low degrees of addition, for example C6H2 or C6Br, to add further g
roups to form C6H4 or C6Br2 for example. This feature results in the p
roduction of chains, formed by the edge sharing of these hexagonal fac
es, which progressively increase in length as the extent of addition i
ncreases. Particularly stable structures are formed if these chains el
iminate the chain ends to form cyclic structures. Examples include the
skew pentagonal pyramids in C(60)X(6), C(60)X(12) and C(60)X(18), the
crowns in C(60)X(18) and C(60)X(36), and the rhombicuboctahedral patt
ern in C(60)X(24). The ring compounds C-60(ring)(1-6), formed by addit
ions to hex-hex edges, have rings occupying octahedral sites about the
C-60.