Chemistry Reference
In-Depth Information
FIGURE 18.1
Polyynes in methanol produced by graphite arcing. Top: Chroma-
togram of the mixture. Bottom: Overlapped absorption spectra of the polyynes
series. The peak at 223 nm is due to C
8
H
2
. The concentration is approximately
3.9
10
6
M.
the relative electronic absorption spectra (overlapped) of all the detected
polyynes. It can be observed that the most abundant polyyne, C
8
H
2
, reaches
an A value of 75mAU. Using the Lambert-Beer law and knowing that the
molar extinction coefficient of this molecule is 190,546 L mol
1
cm
1
, it can
be calculated a concentration of 3.9
10
6
M. If 100ml of this solution are
concentrated by evaporation under reduced pressure to about 9ml, then
a concentration of 4.5
10
5
M for the same molecular species can be easily
achieved as shown in
Figure 18.2
.
18.2.2 P
OLYYNES
:I
SOLATION AS
A
CETYLIDES
Polyynes prepared in decalin solution by arcing offer the advantage to
start from relatively highly concentrated solutions, which can be further
concentrated by low pressure distillation. However, the drawback of decalin
is that it is a relatively viscous and high boiling liquid which is filtered with
more difficulty in comparison to methanol or ethanol and requires higher
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