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Formation of Radical Cations from 1 2- and 1 4-Dimethoxybenzene by Electron Transfer to TI2+ and Ag2+ in Aqueous Solution.

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li [nmlFig. 1. a) Time-dependence of the C D spectra of (I) in 95 %ethanol. c z
mol/l; 20°C; d=20mm (h>260nm), d = 2 m m (ht260nm); t , = 5 , 30, 60,
100, 150, 230min after dissolution of ( I ) . b) Time-dependence of the UV
spectra of ( 1 ) in 95% ethanol. C S I O - ~ mol/l; 20°C; d = 2 0 m m , t , = 5 , 15,
35, 70,120. 240,500 min after dissolution of ( I ) .
difference (ED) diagramsf2](Fig. 2), and ellipticity diagrams
(Fig. 3). Plotting of extinction values &(ti) taken from the timedependent UV spectra (Fig. 1 b) at a particular wavelength
uersus the analogous &(ti) values taken at another wavelength
yields an E diagram. For small changes, but very different
absolute values, of &(ti) (as in Fig. 1b) it is better to calculate
the differences A f Z x = E ~ ( t i ) - E ~ ( t in
l ) each case and to plot
them against one another ( E D diagrams, Fig. 2).
If [el values or dichroic amplitudes are taken from the
time-dependent CD spectra (Fig. 1 a) and plotted against each
other in analogous manner then ellipticity diagrams'' are
obtained (Fig. 3). In the case of spectroscopically uniform
reactions all these diagrams should afford straight lines for
any combination of wavelengths; this requirement is well
satisfied in the present case.
AEk-
-010
-0.06
-100
-60
-80
-40
-20
0
20
Dichroic amplitude [mml
1
lj
-100
360
co
O
I
t -20
-
40
1
158
60
Fig. 3. Ellipticity diagrams: dichroic amplitudes at 275 nm taken from
Fig. 1a and plotted against the corresponding values at eight other wavelengths
(nonlinear time scale as auxiliary axis).
dissymmetric CSSC grouping or with strict mechanical coupling to this twisting (linear dependence), then the conformational change occurring on transition from the crystal to
solution takes place in a spectroscopically uniform manner.
Thus the assumption is confirmed that twisting of the disulfide
group-accompanied by conformational changes of the entire
heterodetic ring-occurs in ( I ) on transition from the crystal
to solution. The possible E / Z isomerization of the urethane
bond does not appear to be incorporated in the observed
temperature dependence of the CD and UV spectra of (I).
Many of the spectroscopic data for peptides and other
nonrigid molecules which were previously considered to be
independent of time should be subjected to critical scrutiny.
The relevance of these phenomena, which we have already
observed for various other examples, to the interpretation
of X-ray structure analyses and of structure-activity relations
is obvious.
Received: March 6, 1975 [Z 208 IE]
German version: Angew. Chem. 87, 448 (1975)
CAS Registry numbers:
( 1 ) . 52071-43-9
[1] a) G. Jung and M. Ottnad, Angew. Chem. 86, 856 (1974); Angew. Chem.
internat. Edit. 13, 818 (1974); b) M. Ormad, C. Ortnad. P. Hartfer, and
G.Jun~/.Tetrahedron,31,1155(1975);c)M.Ortnad.
P. Harrrer.and G.Juny.
Hoppe-Seyler's Z. Physiol. Chem., in press, and references cited therein.
[2] a) H. Mauser, 2. Naturforsch. 23b, 1021, 1025 (1968); b) H. Lachmann,
H. Mauser, F . Schneider, and H . Wenck, ibid. 26b, 629 (1971); c) H.
Lachmann, Dissertation, Universitat Tubingen 1973: d) H. Mauser: Formale Kinetik. Bertelsmann-Universitiits-Verlag. Dusseldorf 1974: e) H .
Lachmann, to he published.
Formation of Radical Cations from 1,2- and 1 , 4
Dimethoxybenzene by Electron Transfer to TI * and
Ag2+ in Aqueous Solution.
A Pulse Radiolysis and in situ Radiolysis EPR Study
+
-0 02
By Prrer O'Neill, Steen Stc~cnkon.and
Dietrich Schulte-Frohlindri'l
Fig. 2. Extinction difference diagrams: the values are taken from automatically
repeated UV spectra (recordingconditions as for Fig. 1 b, except ford = 50 m m :
nonlinear time scale as auxiliary axis).
In a previous publication"' it was shown that T1° reacts
with 1,4-dicyanobenzene and 1,4-dinitrobenzene, even in
strongly acidic solution, by transfer of an electron to produce
radical anions and T1'. We now report electron transfer
from 1,2- and 1,4-dirnethoxybenzene (I) and (2), respectively,
to TI'' and Agz+ to yield radical cations and T1' and Ag'.
[*I
Consideration of models of (I) show that mutually independent isomerizations of the disulfide group and the intraannular
peptide bonds are impossible. If all processes within the heterodetic ring occur synchronously with twisting of ihc inherently
430
Dr. P. ONeill, Dr. S. Steenken, and
Prof. Dr. D. Schulte-Frohlinde [ +]
Institut fur Strahlenchemie im Max-Planck-Institut
fur Kohlenforschung
433 Mulheim/Ruhr, Stiftstrasse 34-36 (Germany)
[+] To whom correspondence should be addressed
Angew. Chrm. internat. Edit. 1 Vol. 14 ( 1 9 7 5 )
No. 6
The radical cations were identified by in situ radiolysis EPR"'.
The optical absorption spectra and lifetimes of the radical
cations and the rate constants reported (Table 1 ) were determined by pulse radiolysis. The aqueous solutions used were
saturated with N,O and contained
mol/l ofTI,SO, and
mol/l of ( / ) or (2). The pH was adjusted with perchloric
acid.
Irradiation of water with 2.8 MeV electrons produces the
species e& (2.7). OH (2.8), H (0.55). H, (0.45), H,O, (0.7).
H' (3.2), O H - (0.5).The values in parentheses indicate the
number of particles formed per I00 eV of absorbed energy.
The hydrated electron ea; reacts with N,O to produce OH
radicals :
erq
+
+
N,O
H,O
+
OH
+ OH + N,
Thus in N,O saturated solutions the radiolytically formed
primary radical species present immediately after the pulse
comprise 90% OH radicals and 10% H atoms. The OH
radicals react with TI' cia electron transfer to yield OH- and
TI2 '13.41.
OH
+ TI'
+
OH-
+
+ H*:
H,O+[TIOH]'
pK=4.7
On production of T1" in the presence of (/), using the
procedure described, species (3) was observed which is characterized by an absorption spectrum with maxima at 290 and
400 nm and a lifetime of several tenths of a second. In the
presence of (2) species ( 4 ) was detected. ( 4 ) has absorption
maxima at 300, 440. and 460 nm and a lifetime of several
seconds. Using the in situ radiolysis EPR methodt2],( 3 ) and
( 4 ) were identified as the radical cations of ( / ) and (Z),
respectively. ( 4 ) exists in t r a n ~and cis forms; at 5"C, the
trans/cis ratio was found to be 1.12 : l . ( 3 ) exists in only one
isomeric form, probably trcrns.
trans- i 4 i
cis-lli
The spectral parameters of trans-(4) and cis-(4) in aqueous
solution are very similar to those''] in concentrated sulfuric
acid.
Table I . Rate constants I, in aqueous solution at 20°C
k [I m o l - '
Rcaction
TI' + OH 4 [TIOH]'
[TIOH]' + H ' 4 TI'*
TI" + H i 0
[TIOH]'
TIz* + ( I ) + T I * (31
TI" + (-7)
TI' + ( 4 )
[TIOH](1)
[TIOH]*
(2)
+
+
Received: March 20. 1975 [Z 209 IE]
German cersion: Angew. Chem. X7.117 11975)
CAS Registry numbers:
( I ). 91-16-7: (-7 ), 150-78-7: ( 3 ). 5501 2-64. I : ( 4 1, 34478-03-0.
TI'.. 14x77-ZX-7: Ag". 15046-91-0
+ TI'.
This reaction occurs preferentially at pH values below 4.7"l.
Above this value the complex [TIOH]+[51 is formed. The
ions TI2' and [TIOH]' are correlated ria the
TI'+
In the absence of TI' under otherwise identical conditions
no radical cations were observed at the end of the pulse.
From this it follows that the OH radical does not in the primary
step react by electron transfer with ( I ) and ( 2 ) . The dependence of the radical cation concentration, as measured by pulse
radiolysis, upon the pH value of the solution corresponds to
that of the species TI'+. Hence it is concluded that only TI"
reacts completely with ( 1 ) and (2) by electron transfer, in
contrast to [TlOH]'. The complex [TIOH]' reacts with ( I )
and (2) with about the same k values as TI" (Table 1). Thus
the presence of ( I ) or ( 2 ) does not disturb the equilibrium
between TI2+ and [TIOH]'. The radical cations ( 3 J and ( 4 )
can also be generated by reaction with Ag2+, produced[7.x1
by oxidation of Ag' with OH. or by reaction with SO;-.
+
+ H20
+ H'
SC']
1.0 x 10"'
1.4 x 10"'
3.5 x 10' [a]
6.0 x 10'
6.5 x 10'
1.2 x 109
4.5 x
IOH
E . A. Rohin.sori and D. S~hirlrr-F~oh/rnile.
J. C. S. Faraday Trans I.
119731.
K . Eihrn and R . W Ft.ssenden, J. Chem. Phys. 7 5 . I I86 (1971).
B. C e r c r k , M. Ehrvr, and A J . Swul1ow. J. Chem. SOC. A 1966. 612.
H . A . Schwurr, D. Cornstock. J . K . Yc~tidrll.and R . W Dodson. J. Phys.
Chem. 7X. 488 (I970).
P . O'NPIII and D. S c / i n l r r - f ~ n / i / i r i ~J./ ~C~. . S Cheni. Comm. iY75. 3x7
W F. Furhes and P . D. Su11i~u11,Can. J. Chem. 44, 1501 (1966).
J . Pukirs, W Roehkr. and A. H m g l r i n . Ber. Bunsenges. Phys. Chem.
7 2 . 842 ( 1 968).
C . C. Barker and P . FoIv~c~.~.
Trans. Faraday Soc. 66. 1661 (1970).
6Y. 707
Mode of Formation of Triphenylverdazyl from Triphenylverdazylium Salts or from Triphenylformazan
By E . A . Ponomareva, P. % Tarassenko, and G . F . Dvorko"]
1,3,5-TriphenylverdazyIiumbromide ( 1 ) formed from triphenylformazan (6), formaldehyde, and HBr is converted
quantitatively into the radical 1,3,5-triphenylverdazyl ( 5 ) by
treatment with NaOH and C H 2 0 . The reaction mechanism
was hitherto unknown(']. In this communication we report
experiments intended to elucidate the individual steps of this
and similar reactions.
We have found that in the absence of C H 2 0 compound
( I ) reacts with an equimolar amount of NaOH in a stream
of 0, or N2, two thirds undergoing conversion into ( 5 )
and one third into 5-formyl-l,3,5-triphenylformazan(3). An
excess of NaOH does not alter the yield of radical, but compound ( 6 ) is obtained instead of compound (3) [in the same
yield as ( 3 ) in the above reaction]. Atmospheric oxidation
of ( 5 ) affords the aldehyde ( 3 ) .which is decomposed rapidly
andquantitatively into ( 6 )and formate by theaction of NaOHf2!
In our case ( 5 ) is not oxidized to (31. The experiments werc
performed in DMF (or CH,CN)iH,O ( 4 : l v i v ) ; the concentration of (51 was monitored by spectroscopy
= 720.
log E = 3.63).
The formation of two moles of ( 5 ) and one mole of (3)
from three moles of ( I ) and three moles of NaOH can be
explained in terms of the reaction steps (a), (bj, and (c).
(>L,,,.,y
Ref.
~4.51
r51
151
[*] Dor. E. A. Ponomareva
+], DipLChem. P. V. Tarassenko. and
111-G F D\orko
Chemical Faculty of the Kiev Polytechnic Institute
Kiev 56 (USSR)
[ + ] T o whom correspondence should be addressed
43 1
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solutions, ti2, formation, transfer, aqueous, dimethoxybenzol, electro, radical, cation, ag2
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