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Voltammetry of Immobilised Microdroplets Containing p-Chloranil on
Basal Plane Pyrolytic Graphite Electrodes
Debora Giovanelli1, Trevor J. Davies1, Li Jiang2, Timothy G. J. Jones2 and
Richard G. Compton1*
Supporting Information
1
Physical and Theoretical Chemistry Laboratory, University of Oxford,
South Parks Road, Oxford, OX1 3QZ, United Kingdom.
*To whom correspondence should be addressed:
Email: richard.compton@chemistry.oxford.ac.uk
Tel: +44 (0) 1865 275 413
Fax: +44 (0) 1865 275 410
2
Schlumberger Cambridge Research, High Cross, Madingley Road,
Cambridge, CB3 0EL, United Kingdom.
1
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Supporting Information
In the following section we discuss the electrochemical reduction of
TCBQ at a GC electrode in different aprotic solvents, namely DMF, DMSO
and PrCN, in the presence of 0.1 M TBuAP as supporting electrolyte and
compare the results to those obtained using BN as solvent.
Comparison of the electrochemical reduction of TCBQ at GC in BN with
other aprotic solvents (DMF, DMSO and PrCN)
The reduction of TCBQ was also carried out in other aprotic solvents,
namely DMF, DMSO and PrCN in the presence of 0.1 M TBuAP as
supporting electrolyte. The corresponding voltammograms (0.1 V s-1) for
the reduction of 0.5 mM TCBQ at a GC electrode in each different solvent
are overlaid in Figure S1. The potential data are summarised and compared
to those obtained in BN in Table S1 along with the Gutmann donor number,
DN, and the viscosity, , of each solvent.
In all the solvents, two peaks were observed corresponding to the
reduction of TCBQ to the radical anion, followed by reduction to the
dianion. However, variation in the peak potential for the reduction were
seen and a comparison of the reduction peak potential observed for the first
process reveals that Epr is less negative for DMF and DMFO as compared to
BN and PrCN. Solvent effects in the electrochemical reduction of several
p-quinones in aprotic solvents have been reported before [1] and can be
2
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interpreted in terms of increasing stabilisation of the electrode products
(radical anion and di-anion) with increasing donor number of the solvent.
The relative order of donor number DN is [2,3]:
BN < PrCN < DMF ~DMSO
Indeed, a shift towards more positive potentials was found going from the
higher electron donating solvents DMF and DMSO (DN=26.6, and 29.8,
respectively [2]) to BN and PrCN (DN=11.9 and 16.6, respectively [2,3]).
The less magnitude of both signals obtained in DMSO, as compared to
that obtained in the other aprotic solvents, might be accounted for the lower
diffusion coefficient of TCBQ in DMSO [4] as a result of its higher
viscosity (see Table S1, [5]).
Figure S1: Cyclic voltammograms (0.1 V s-1) recorded at a GC electrode (3 mm
diameter) for the reduction of 0.5 mM TCBQ in homogeneous solutions of DMF, DMSO
and PrCN all containing 0.1 M TBuAP as supporting electrolyte.
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This journal is © the Owner Societies 2004
Electronic supplementary information for Physical Chemistry Chemical
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Table S1: Potentials (vs. Pt) for the reduction of 0.5 mM TCBQ in different aprotic solvents
(0.1 M TBuAP) at a GC (3mm diameter) electrode and solvent donor number (DN, [2,3])
and viscosity (, [5]).
Solvent

DN
/cP
DMSO
2
Epr1
Epo1
Emid1
Ep1
Epr2
/V
/V
/V
mV
/V
/V
Epo2
Emid2
Ep2
/V
/mV
29.8
-0.193 -0.123 -0.158
70
-1.02
-0.93
-0.97
90
DMF
0.796
27
-0.120 -0.023 -0.071
97
-0.99
-0.89
-0.93
100
PrCN
0.515
16.6
-0.214 -0.112 -0.179
71
-1.11
-1.02
-1.06
90
BNa
1.24
11.9
-0.273 -0.173 -0.233
100
-1.07
-0.97
-1.08
101
a
Reduction of 1 mM TCBQ
References:
[1]
K. Sasaki, T. Kashimura, M. Ohura, Y. Ohsaki, N. Ohta, J.
Electrochem. Soc., 1990, 137, 2437.
[2]
W. R. Fawcett, Langmuir, 1989, 5, 661.
[3]
Y. Zhang, Y. Moriguchi, M. Hashimoto, K. Sakata, Anal. Sci., 2001,
17, 675.
[4]
M. Gomez, I. Gonzalez, F. J. Gonzalez, R. Vargas, J. Garza,
Electrochem. Commun., 2003, 5, 12.
[5]
J. F. Coetzee, Recommended Methods for Purification of Solvents
and Tests for Impurities, Pergamon Press, Oxford, 1982, p. 1-59.
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