Cyclic Polyynes: Generation, Characterization, and Reactions - Polyynes: Synthesis, Properties, and Applications - page 110

formation, however, some three-dimensional polycyclic polyynes were pur-
posely generated from their respective organic precursors in the gas phase
and were found to isomerize to the corresponding fullerenes with the same
carbon numbers.
6.3.2 B ICYCLIC AND T RICYCLIC P OLYYNES
Before discussing the structures of ''bicyclic'' and ''tricyclic'' polyynes, one
trivial issue regarding the technical terms should be made clear in order not
to mislead, because the usage of the terms in the literatures discussing these
structures is different from the common organic nomenclature. For exam-
ple, all of the structures 9-13 for C 24 isomers shown in Figure 6.9 are named
''bicyclic'' in the literatures since they possess two macrocyclic rings [18].
However, 9 and 10 should be called ''tricyclic'' and 12 should be a ''tetra-
cyclic'' structure by counting the number of the all rings present in the
structures. Similarly, the ''tricyclic'' structures 14 and 15 (Figure 6.9)
proposed for C 36 isomers [19] should be regarded as ''tetracyclic'' and
''pentacyclic'', respectively, according to the organic names. To avoid the
confusion, however, this review adopts the literature definition: compounds
9-13 are all classified as ''bicyclic'' and 14 and 15 as ''tricyclic''.
Bowers reported on the basis of the average arrival times of the mass-
selected C 20 þ in the ion chromatography that the structure of the most
abundant C 20 þ is monocyclic [18]. However, they observed a small amount
of C 20 þ whose mobility matched those calculated for bicyclic structures such
as 16 and 17 (Figure 6.9) incorporating both sp and sp 2 carbons. It should
be pointed out that 16 possesses two ten-membered polyyne rings in accord
FIGURE 6.9 Bicyclic forms of C 20 and C 24 and tricyclic forms of C 36 .