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groups with carbon vapor and hence can terminate the polyyne chains into
dicyanopolyynes: N
N. It is fascinating to think that similar
synthetic processes leading to these or similar molecules are known to occur
in the outflow of certain carbon-rich giant stars in the space [6,7].
By continuing arcing in liquid nitrogen with graphite electrodes, it is
possible to accumulate the reaction products into the octane trap. This is
C-(C
C)
n
-C
illustrated in
Figure 15.5(C)
where the bands become more intense and
better defined as function of the arcing time. In particular, in Figure 15.5(C)
the concentration of the polyynes can be estimated at about 2.5
10
6
M.
Arcing was stopped when all liquid nitrogen in the reaction flask was
consumed, i.e. disappeared by vaporization. The final spectrum of the prod-
ucts collected in is shown in Figure 15.5(D) with a final total concentration
of polyynes estimated at about 8
10
6
M.
The crude n-octane solution, after filtration, was chromatographed in
the HPLC apparatus (see The complex polyynes mixture
formed by arcing graphite directly into liquid nitrogen was resolved into
six main components whose electronic absorption spectra are shown all
together in Figure 15.6. The three main components are easily and defi-
nitively identified from their electronic absorption spectra and are respec-
tively C
6
N
2,
C
8
N
2
, and C
10
N
2
(see below for further details). The former are
Section 15.2
).
FIGURE 15.6
Electronic absorption spectra of the polyynes formed from graphite
arcing in liquid nitrogen. The liquid chromatographic analysis (HPLC) was able to
separate the mixture into its components. The electronic spectrum of each com-
ponent eluted was recorded by the diode-array detector (DAD). The three main
components are easily and definitively identified from their electronic absorption
spectra and are respectively C
6
N
2
,C
8
N
2
, and C
10
N
2
. The spectra of these three
dicyanopolyynes in the figure are easily identifiable from the longest wavelength
absorption band lying at 233, 260 and 283 nm respectively. There are also other
two minor components in the figure: the hydrogen-terminated polyynes C
8
H
2
,
C
10
H
2
. Furthermore, also C
12
H
2
has been identified although at very low
concentration (not shown in the figure).
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