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are introduced, e.g. by impurities. Stabilization of sp-carbon chain was also
considered inside a carbon nanotube [29,30] or in siliceous molecular sieve
MCM41 [31]. Baughman et al. [32] have calculated the heat of formation
of polyyne[-(C
C)
n
-]/2n to be 106 kJ/at. Such an energetically demanding
process may, perhaps, well proceed electrochemically. Let us assume that
''electrochemical carbyne'' is produced from a molecular precursor CX
y
(X is a general substituent(s)). Depending on the nature of X, the reaction is
either oxidative (4.11a) or reductive (4.11b):
y e
!
yX
þ
,
CX
y
1
=
2n
ð
C
C
Þ
n
þ
ð
4
:
11a
Þ
y e
!
yX
:
CX
y
þ
1
=
2n
ð
C
C
Þ
n
þ
ð
4
:
11b
Þ
The assessment of the driving force follows from the reaction standard
Gibbs free energies
G
0
, calculated by using the corresponding energies of
formation of the reactant CX
y
(
G
R
) and the products (
G
P
) in reactions
(4.11a,b).
G
0
¼
y
G
P
G
R
:
ð
4
:
12
Þ
The
G
0
values can be transformed into the corresponding standard electro-
chemical potentials, E
0
(Eq. 4.1). For instance, the conversion of PTFE
(
365 kJ/mol CF
2
) into polyyne and HF (reaction (4.11b) in a
hypothetical cell with standard hydrogen electrode) would have
G
R
¼
G
0
¼
71 kJ/mol. The corresponding standard redox potential PTFE/polyyne
is E
0
¼
0.74 V, which is just 0.36 V smaller than the standard potential of
PTFE/graphite (E
0
¼
1 V) [3]. Apparently, in terms of the reaction thermo-
dynamics, the ''electrochemical carbyne'' should be easily accessible via
cathodic reduction of PTFE. Analogously, the oxidation of acetylene (
G
R
¼
209.9 kJ/mol) to polyyne (Eq. 4.11a) corresponds to
G
0
¼
2.1 kJ/mol,
E
0
¼
0.02 V.
Unfortunately, reactions (4.11a and 4.11b) do not stop at the stage of
pure polyyne, -(C
C)
n
-, but there are two other pathways of product trans-
formation. Polyyne is unstable against interchain crosslinking, which leads
to sp
2
carbon structures [33]:
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
(4.13)
It occurs at sites where the chains get into the close distance, promoting
covalent interactions. A second mechanism of polyyne transformation
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