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A correlation of solvated electron absorption spectra with the solvent parameter ET(30)
Radiat. Phys. Chem. Vol. 19, No. 2, pp. 151-154, 1982 Printed in Great Britain.
0146-57241821020151-04503.00/0 Pergamon Press Lid.
A CORRELATION OF SOLVATED ELECTRON ABSORPTION SPECTRA WITH THE SOLVENT PARAMETER ET(30) HUGH D. BURROWS Chemistry Department, Universityof Ire, Ile-Ife, Nigeria (Received 21 January 1981) Abstraet--A linear correlation is observed between the energy of solvated electron absorption maxima and the values of the empirical solvent parameter Er(30) for 24 of the 29 solvent systems on which data is available. The correlation spans a wider range of solvent polarity than similar correlations with iodide ion absorption spectra. Of the five solvents which do not give a good correlation, three are amides,.and it is suggested that reported solvated electron spectra in these cases may, instead, be due to radical anion absorptions. 1. I N T R O D U C T I O N WHILST considerable information exists on the electronic spectra of solvated electrons in a wide variety of solvents, tH°) and many attempts have been made to interpret these spectra in terms of the properties of the solvents ~1"9-17) none has been completely succesful in rationalising all of the known optical properties. Two alternative approaches have been adopted. Firstly, detailed theoretical calculations have been carried out, either using a polaron model, in which only longrange interactions are considered, "l) or using a simple particle-in-a-box type model in which only short-range interactions are considered. "5~ The most successful of these calculations have been those in which only short-range interactions are considered, tl4'15~ Qualitative agreement with experimental spectra has been observed. However, lack of data on excited states of solvated electrons has limited the success of these calculations: 12) An alternative approach is to consider empirical correlations between absorption maxima and such solvent properties as static dielectric constant, refractive index, solvent dipole moment, and density. ~9a7~ Such correlations can provide information on the nature of excited states, which can be helpful in designing models for more detailed calculations. In addition, they provide a way of predicting the position of solvated electron maxima in new solvents. The most successful of the empirical correlations have been those in which solvated electron maxima have been related to the absorption maxima of chargetransfer-to-solvent (CTTS) transitions of inorganic ions. Following the initial suggestion of Franck and Platzman, ~ls~ various w o r k e r s ~2''°'~9'2°) have
shown a linear relationship between the energy of solvated electron maxima and the CTTS absorptions of iodide ion. The most complete compilation has been that of Fox and Hayon t2''°~ who found a good linear correlation with the first absorption of iodide ion for 37 pure solvent and mixed solvent systems. The biggest problems associated with this technique are the rather limited solubility of iodide ions in non-polar solvents, and the fact that the iodide CTTS absorption falls in the far UV region, where problems can arise from overlapping transitions. Certain other charge-transfer transitions also show considerable solvent sensitivity, and these transitions have been used to obtain empirical parameters of solvent polarity: 22~ The most important of these parameters are the Z scale of Kosower based on the intermolecular chargetransfer absorption of pyridinium iodides, ~23~ and the Er(30) scale of Dimroth et al. based on the intramolecular charge-transfer transition of pyridinium phenol betaines: 24) the Z and Er(30) scales are linearly related, t22~ and values can be determined for both polar and non-polar solvents. In this note, an attempt is made to see whether solvated electron absorption maxima can be related to such empirical solvent parameters in order to extend the range of charge-transfer correlations to less polar solvents. For this purpose the parameter Er(30) has been chosen, as more data is available on it. 2. R E S U L T S A N D D I S C U S S I O N In Table 1, literature data are presented on solvated electron absorption maxima and Er(30) values for 29 pure and mixed solvent systems. A
151
H. D. BuRRows
152
TABLE I. SOLVATEDELECTRONABSORPTIONMAXIMAAND ET(30) VALUESFOR VARIOUSSOLVENTS
,o.
1.
2. S. 4. 5. 6. 7. 8. 9. I0. ii 12 13 14 15 16 17 18 19 20. 21. 22. 28. 24. ~5. 26. 27. 28. 29.
Sol,e,t
~.~01/°_1 !
Ethylene g l y o o l Dtmethylacetsmlde Methanol n-Butanol 70~ethanol-Water 64%Ethanol-Water 2-Methoxyethanol 47~Ethanol-Water
17174 6560 ~
Water 47~Dioxane-Water 26~Dioxane-Water Ethanol 90~Ethanol-Water 80~Ethanol-Water 70~,~Isopropanol-Water n-Propanol 79~Isopropanol-Water 66~D1oxane-Water Isopropanol 79~loxane-Water 91~Dioxane-Water Dioxane
13890 18890 15890 13707 13600 13600 13600 13465 12750 12600 12014 12050 10500 9090 ~
16581
14575 14560 14100 13968 S 13900
t-Butanol Dimethylformamlde Dimetho~ethane Tetrahydrofuran Diethylether Hexamethylphosphor~mlde 5-~ethyloctane
9302 5932 5265 4765 4760 4300 4762
S ~
~ ~
ET!30) a
66.3 42.2 55.6 50.2 57.2 ~ 54.7 ~ 32.5 55.9 ~ 63.1 54.2 ~ 57.8 ~ 31.9 52.9 53.7 ~ 52.4 50.7 51.7 ~3.7 48.5 52.4 46.3 ~ 36.0 45.9 45.8 58.2 57.4 34.6 39.0 50.9 !
Data on s o l v a t e d e l e c t r o n spect~a taken from r e f . 2 u n l e s s otherwise s t a t e d ; ~ r e f . 4 ; £ r e £ . l O ; ~ r e f . 5 ; I r e f . 9 ; r e £ . 8 ; ~ ET(30) v a l u e s taken from r e f . 2 2 u n l e s s otherwise s t a t e d ; ~ r e f . 2 4 ; A v a l u e f o r n-hexane used from r e f . 2 2 .
reasonable linear correlation is observed between these, with the exception of water, n-butanol, dimethylformamide, dimethylacetamide, and hexamethylphosphoramide (points 2, 4, 9, 24 and 28, respectively). The data for all but these five solvents was fitted by least squares (correlation coefficient 0.944) to the line 17max(eJo,v)= 429Er(30) - 9270 (cm-l). Conversion of Er(30) values from kcal mol -~ to
cm -1 gives a slope of 1.22, somewhat smaller than the slope of 1.59 observed with iodide CTTS absorptions. ('°> The present correlation spans a rather wider range of solvent polarity than the correlation with iodide spectra of Fox and H a y , n , "°) and may be useful in predicting solvated electron absorption maxima in solvents of low polarity. In addition, solvated electron absorption maxima may be used as alternatives to Z and Er(30) scales as empirical measures of solvent polarity.
Solvent parameter Er(30)
oC l
15 T
E
153
0 ~ 5
I D~
-
I 023
~30
21
) ~,o ~
29
5
0
30
071
0 0 025
0 2f. ?
I
t,O
I
I
50
60
ET(30) kcal mote -1
FIG. I. Plot of solvated electron absorption maxima against Er(30) values for various solvent systems. Numbers correspond to solvents listed in Table 1. The fact that a correlation is obseved for 24 of the solvents raises interesting questions on the origin of the absorptions in the two cases. Solvent shifts in electronic transitions may be attributed to the different polarities of ground and excited states. In the Franck-Condon state which is excited, the solvent orientation is identical to the ground state, so that differences in polarity lead to the observed shifts. Solvated electron spectra are generally attributed to a 2p<---ls transition of the electron within its solvation cavity, although the width of the absorption bands suggests that this is rather an oversimplification. (2~) The excited state, however, probably has the electron in an orbital which can interact more strongly with the solvent molecules than the ground state. The betaines, in contrast, have a highly polar ground state and a relatively non-polar excited state. There would, thus, be expected to be differences in solvation in the two cases. In addition, the solvent cavity surrounding the electron would be expected to be somewhat smaller than that surrounding the betaine. The observed correlation at first sight thus seems rather suprising. In part it must reflect some long-range solvent interactions, i.e. with solvent molecules outside the primary solvation sphere. Considering the five solvents which do not fit the correlation, it is possible that the differences arise from different local solvent structure in the two cases. However, it is noteworthy that three of these solvents are amides. These three solvents also do not fit Freeman's empirical correlation, t4'9> and hexamethylphosphoramide gives only a poor fit in the correlation of Fox and Hayon. "°~ It has been suggested in the case of hexamethylphosphoramide (26~ that the low value for the energy of
the solvated electron absorption results from the electron being trapped in an alkane-like region of the solvent. In contrast, polar molecules such as the betaines would be expected to be solubilized in a more polar region of the solvent. However, an alternative explanation is possible. Assignment of absorptions in pulse radiolysis experiments to solvated electrons is based largely on their reactivities towards reducible substrates such as nitrous oxide and aromatic compounds. On such a kinetic basis, it is difficult to distinguish between solvated electrons, where the electron is in a cavity defined by several solvent molecules, and solvent radical anions, or anion dimers, where the electron is localised in a molecular orbital on one or two solvent molecules. This latter situation is likely to be favoured where the solvent molecule has a low-lying antibonding orbital, e.g. a 7r*orbital. It is, thus, possible that the absorptions with the amides are due to solvent radical anions rather than solvated electrons. Broad absorptions of solvent derived reducing species have been observed in the pulse radiolysis of acetone, (27~and acetonitrile, <2s} and in both cases the absorption appears to be due to the solvent radical anion. It is noteworthy that solvated electrons in ethanol react rapidly with amides to give, presumably, radical anions. (4> The nature of the solutions obtained on dissolving alkali metals in hexamethylphosphoramide is still not settled. The broad absorption observed in these systems has been assigned both to solvent radical anion, (29>and to a solvated electron. °°~ The assignment in the latter case is based largely on the similarity of the absorption to that observed in solutions of alkali metals in liquid amines. Final assignment of these
154
H.D. BURROWS 13. J. JORTNER, Ber. Bunsenges Phys. Chem. 1971, 75, 696. 14. N. R. KESTNER and J. LOGAN, J. phys. Chem. 1975, 79, 2815. 15. See, for example, M. DEBACKER,J.-P. LELIEUR and G. LEPOUTRE, J. phys. Chem. 1978, 82, 2701. 16. P. R. TREMAINEand R. S. DIXON, J. phys. Chem. 1978 82, 224. 17. FARHATAZIZ,Radiat. Phys. Chem. 1980, 15, 503. 18. J. FRANCKand R. L. PLATZMAN,Z. Phys. 1954,138, 411. 19. M. J. BLANDAMER,R. CATTERALL, L. SHIELDS and M. C. R. SYMONS, J. Chem. Soc. 1964, 4357. REFERENCES 20. M. ANaAR and E. J. HART, J. phys. Chem. 1965, 69, 1244. F. S. DAINTON, Chem. Soc. Rev. 1975, 4, 323. M. F. Fox and E. HAYON, Chem. Phys. Lett. 1974, 21. N. N. NAGENDRAPPA, R. OLINGER and U. SCHINDERWORF, Z. physik. Chem. (Frankfurt am Main), 25,511. 1974, 88, 323. R. R. HENTZ and G. A. KENNEY-WALLACE,Jr. phys. 22. E. M. KOSOWER,An Introduction to Physical Organic Chem. 1974, 78,514. Chemistry, pp. 294-333, Wiley, New York 1968. J. F. GAVLAS,F. Y. Jou and L. M. DORFMAN,J. phys. 23. E. M. KOSOWER,J. Am. Chem. Soc. 1958, 80, 3253. Chem. 1974, 78, 2631. 24. K. DIMROTH, C. REICHARDT, T. SIEPMANN and F. H. NAUTA and C. VANHUIS,J. Chem. Soc., Faraday BOHLMANN, Ann. 1963, 661, 1. Trans. 1, 1972, 68, 647. J. H. BAXENDALE, C. BELL and P. WARDMAN, J. 25. M. C. R. SYMONS, Chem. Soc. Rev. 1976, 5,337. 26. G. A. KENNEY-WALLACE,Acc. Chem. Res. 1978, 11, Chem. Soc., Faraday Trans. 1, 1973, 69, 776. 433. W. A. SEDDON, J. W. FLETCHERand R. CATTERALL, 27. M. A. J. RODGERS,J. Chem. Soc., Faraday Trans. l, Can. J. Chem. 1977, 55, 2017. 1972, 68, 1278. H. A. GILLIS, N. V. KLASSEN and R. J. WOODS, Can. 28. I. P. BELL, M. A. J. RODGERSand H. D. BORROWS,3". J. Chem. 1977, 55, 2022. Chem. Soc., Faraday Trans. I, 1977, 73, 315. G. R. FREEMAN,J. phys. Chem. 1973, 77, 7. 29. H. NORMANT,Angew. Chem. Int. Ed. 1967, 6, 1046. M. F. Fox and E. HAYON, J. Chem. Soc. Faraday 30. J. M. BROOKS and R. R. DEWALD, J. phys. Chem. Trans. 1, 1976, 72, 1990. 1968, 72, 2655. M. F. DEIGEN, Zh. Exp. Theor. Phys. U.S.S.R. 1954, 31. J. W. FLETCHER and W. A. SEDDON, Disc. Faraday 26, 300. Soc. 1977, 63, 18. D. A. COPELAND, N. R. KESTNER and J. JORTNER, J. 32. J. H. BAXENDALE,Can. J. Chem. 1977, 55, 1996. chem. Phys. 1970, 53, 1189.
absorptions is likely to c o m e from conductivity experiments, and from studies on mixed solvent systems. (3" It is worth noting that in pulse conductivity studies on binary alkane-demethylformamide systems, the results are consistent with an electron being captured by a single dimethylf o r m a m i d e molecule, although the interpretation is not unequivocal. (32)
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. l 1. 12.
0146-57241821020151-04503.00/0 Pergamon Press Lid.
A CORRELATION OF SOLVATED ELECTRON ABSORPTION SPECTRA WITH THE SOLVENT PARAMETER ET(30) HUGH D. BURROWS Chemistry Department, Universityof Ire, Ile-Ife, Nigeria (Received 21 January 1981) Abstraet--A linear correlation is observed between the energy of solvated electron absorption maxima and the values of the empirical solvent parameter Er(30) for 24 of the 29 solvent systems on which data is available. The correlation spans a wider range of solvent polarity than similar correlations with iodide ion absorption spectra. Of the five solvents which do not give a good correlation, three are amides,.and it is suggested that reported solvated electron spectra in these cases may, instead, be due to radical anion absorptions. 1. I N T R O D U C T I O N WHILST considerable information exists on the electronic spectra of solvated electrons in a wide variety of solvents, tH°) and many attempts have been made to interpret these spectra in terms of the properties of the solvents ~1"9-17) none has been completely succesful in rationalising all of the known optical properties. Two alternative approaches have been adopted. Firstly, detailed theoretical calculations have been carried out, either using a polaron model, in which only longrange interactions are considered, "l) or using a simple particle-in-a-box type model in which only short-range interactions are considered. "5~ The most successful of these calculations have been those in which only short-range interactions are considered, tl4'15~ Qualitative agreement with experimental spectra has been observed. However, lack of data on excited states of solvated electrons has limited the success of these calculations: 12) An alternative approach is to consider empirical correlations between absorption maxima and such solvent properties as static dielectric constant, refractive index, solvent dipole moment, and density. ~9a7~ Such correlations can provide information on the nature of excited states, which can be helpful in designing models for more detailed calculations. In addition, they provide a way of predicting the position of solvated electron maxima in new solvents. The most successful of the empirical correlations have been those in which solvated electron maxima have been related to the absorption maxima of chargetransfer-to-solvent (CTTS) transitions of inorganic ions. Following the initial suggestion of Franck and Platzman, ~ls~ various w o r k e r s ~2''°'~9'2°) have
shown a linear relationship between the energy of solvated electron maxima and the CTTS absorptions of iodide ion. The most complete compilation has been that of Fox and Hayon t2''°~ who found a good linear correlation with the first absorption of iodide ion for 37 pure solvent and mixed solvent systems. The biggest problems associated with this technique are the rather limited solubility of iodide ions in non-polar solvents, and the fact that the iodide CTTS absorption falls in the far UV region, where problems can arise from overlapping transitions. Certain other charge-transfer transitions also show considerable solvent sensitivity, and these transitions have been used to obtain empirical parameters of solvent polarity: 22~ The most important of these parameters are the Z scale of Kosower based on the intermolecular chargetransfer absorption of pyridinium iodides, ~23~ and the Er(30) scale of Dimroth et al. based on the intramolecular charge-transfer transition of pyridinium phenol betaines: 24) the Z and Er(30) scales are linearly related, t22~ and values can be determined for both polar and non-polar solvents. In this note, an attempt is made to see whether solvated electron absorption maxima can be related to such empirical solvent parameters in order to extend the range of charge-transfer correlations to less polar solvents. For this purpose the parameter Er(30) has been chosen, as more data is available on it. 2. R E S U L T S A N D D I S C U S S I O N In Table 1, literature data are presented on solvated electron absorption maxima and Er(30) values for 29 pure and mixed solvent systems. A
151
H. D. BuRRows
152
TABLE I. SOLVATEDELECTRONABSORPTIONMAXIMAAND ET(30) VALUESFOR VARIOUSSOLVENTS
,o.
1.
2. S. 4. 5. 6. 7. 8. 9. I0. ii 12 13 14 15 16 17 18 19 20. 21. 22. 28. 24. ~5. 26. 27. 28. 29.
Sol,e,t
~.~01/°_1 !
Ethylene g l y o o l Dtmethylacetsmlde Methanol n-Butanol 70~ethanol-Water 64%Ethanol-Water 2-Methoxyethanol 47~Ethanol-Water
17174 6560 ~
Water 47~Dioxane-Water 26~Dioxane-Water Ethanol 90~Ethanol-Water 80~Ethanol-Water 70~,~Isopropanol-Water n-Propanol 79~Isopropanol-Water 66~D1oxane-Water Isopropanol 79~loxane-Water 91~Dioxane-Water Dioxane
13890 18890 15890 13707 13600 13600 13600 13465 12750 12600 12014 12050 10500 9090 ~
16581
14575 14560 14100 13968 S 13900
t-Butanol Dimethylformamlde Dimetho~ethane Tetrahydrofuran Diethylether Hexamethylphosphor~mlde 5-~ethyloctane
9302 5932 5265 4765 4760 4300 4762
S ~
~ ~
ET!30) a
66.3 42.2 55.6 50.2 57.2 ~ 54.7 ~ 32.5 55.9 ~ 63.1 54.2 ~ 57.8 ~ 31.9 52.9 53.7 ~ 52.4 50.7 51.7 ~3.7 48.5 52.4 46.3 ~ 36.0 45.9 45.8 58.2 57.4 34.6 39.0 50.9 !
Data on s o l v a t e d e l e c t r o n spect~a taken from r e f . 2 u n l e s s otherwise s t a t e d ; ~ r e f . 4 ; £ r e £ . l O ; ~ r e f . 5 ; I r e f . 9 ; r e £ . 8 ; ~ ET(30) v a l u e s taken from r e f . 2 2 u n l e s s otherwise s t a t e d ; ~ r e f . 2 4 ; A v a l u e f o r n-hexane used from r e f . 2 2 .
reasonable linear correlation is observed between these, with the exception of water, n-butanol, dimethylformamide, dimethylacetamide, and hexamethylphosphoramide (points 2, 4, 9, 24 and 28, respectively). The data for all but these five solvents was fitted by least squares (correlation coefficient 0.944) to the line 17max(eJo,v)= 429Er(30) - 9270 (cm-l). Conversion of Er(30) values from kcal mol -~ to
cm -1 gives a slope of 1.22, somewhat smaller than the slope of 1.59 observed with iodide CTTS absorptions. ('°> The present correlation spans a rather wider range of solvent polarity than the correlation with iodide spectra of Fox and H a y , n , "°) and may be useful in predicting solvated electron absorption maxima in solvents of low polarity. In addition, solvated electron absorption maxima may be used as alternatives to Z and Er(30) scales as empirical measures of solvent polarity.
Solvent parameter Er(30)
oC l
15 T
E
153
0 ~ 5
I D~
-
I 023
~30
21
) ~,o ~
29
5
0
30
071
0 0 025
0 2f. ?
I
t,O
I
I
50
60
ET(30) kcal mote -1
FIG. I. Plot of solvated electron absorption maxima against Er(30) values for various solvent systems. Numbers correspond to solvents listed in Table 1. The fact that a correlation is obseved for 24 of the solvents raises interesting questions on the origin of the absorptions in the two cases. Solvent shifts in electronic transitions may be attributed to the different polarities of ground and excited states. In the Franck-Condon state which is excited, the solvent orientation is identical to the ground state, so that differences in polarity lead to the observed shifts. Solvated electron spectra are generally attributed to a 2p<---ls transition of the electron within its solvation cavity, although the width of the absorption bands suggests that this is rather an oversimplification. (2~) The excited state, however, probably has the electron in an orbital which can interact more strongly with the solvent molecules than the ground state. The betaines, in contrast, have a highly polar ground state and a relatively non-polar excited state. There would, thus, be expected to be differences in solvation in the two cases. In addition, the solvent cavity surrounding the electron would be expected to be somewhat smaller than that surrounding the betaine. The observed correlation at first sight thus seems rather suprising. In part it must reflect some long-range solvent interactions, i.e. with solvent molecules outside the primary solvation sphere. Considering the five solvents which do not fit the correlation, it is possible that the differences arise from different local solvent structure in the two cases. However, it is noteworthy that three of these solvents are amides. These three solvents also do not fit Freeman's empirical correlation, t4'9> and hexamethylphosphoramide gives only a poor fit in the correlation of Fox and Hayon. "°~ It has been suggested in the case of hexamethylphosphoramide (26~ that the low value for the energy of
the solvated electron absorption results from the electron being trapped in an alkane-like region of the solvent. In contrast, polar molecules such as the betaines would be expected to be solubilized in a more polar region of the solvent. However, an alternative explanation is possible. Assignment of absorptions in pulse radiolysis experiments to solvated electrons is based largely on their reactivities towards reducible substrates such as nitrous oxide and aromatic compounds. On such a kinetic basis, it is difficult to distinguish between solvated electrons, where the electron is in a cavity defined by several solvent molecules, and solvent radical anions, or anion dimers, where the electron is localised in a molecular orbital on one or two solvent molecules. This latter situation is likely to be favoured where the solvent molecule has a low-lying antibonding orbital, e.g. a 7r*orbital. It is, thus, possible that the absorptions with the amides are due to solvent radical anions rather than solvated electrons. Broad absorptions of solvent derived reducing species have been observed in the pulse radiolysis of acetone, (27~and acetonitrile, <2s} and in both cases the absorption appears to be due to the solvent radical anion. It is noteworthy that solvated electrons in ethanol react rapidly with amides to give, presumably, radical anions. (4> The nature of the solutions obtained on dissolving alkali metals in hexamethylphosphoramide is still not settled. The broad absorption observed in these systems has been assigned both to solvent radical anion, (29>and to a solvated electron. °°~ The assignment in the latter case is based largely on the similarity of the absorption to that observed in solutions of alkali metals in liquid amines. Final assignment of these
154
H.D. BURROWS 13. J. JORTNER, Ber. Bunsenges Phys. Chem. 1971, 75, 696. 14. N. R. KESTNER and J. LOGAN, J. phys. Chem. 1975, 79, 2815. 15. See, for example, M. DEBACKER,J.-P. LELIEUR and G. LEPOUTRE, J. phys. Chem. 1978, 82, 2701. 16. P. R. TREMAINEand R. S. DIXON, J. phys. Chem. 1978 82, 224. 17. FARHATAZIZ,Radiat. Phys. Chem. 1980, 15, 503. 18. J. FRANCKand R. L. PLATZMAN,Z. Phys. 1954,138, 411. 19. M. J. BLANDAMER,R. CATTERALL, L. SHIELDS and M. C. R. SYMONS, J. Chem. Soc. 1964, 4357. REFERENCES 20. M. ANaAR and E. J. HART, J. phys. Chem. 1965, 69, 1244. F. S. DAINTON, Chem. Soc. Rev. 1975, 4, 323. M. F. Fox and E. HAYON, Chem. Phys. Lett. 1974, 21. N. N. NAGENDRAPPA, R. OLINGER and U. SCHINDERWORF, Z. physik. Chem. (Frankfurt am Main), 25,511. 1974, 88, 323. R. R. HENTZ and G. A. KENNEY-WALLACE,Jr. phys. 22. E. M. KOSOWER,An Introduction to Physical Organic Chem. 1974, 78,514. Chemistry, pp. 294-333, Wiley, New York 1968. J. F. GAVLAS,F. Y. Jou and L. M. DORFMAN,J. phys. 23. E. M. KOSOWER,J. Am. Chem. Soc. 1958, 80, 3253. Chem. 1974, 78, 2631. 24. K. DIMROTH, C. REICHARDT, T. SIEPMANN and F. H. NAUTA and C. VANHUIS,J. Chem. Soc., Faraday BOHLMANN, Ann. 1963, 661, 1. Trans. 1, 1972, 68, 647. J. H. BAXENDALE, C. BELL and P. WARDMAN, J. 25. M. C. R. SYMONS, Chem. Soc. Rev. 1976, 5,337. 26. G. A. KENNEY-WALLACE,Acc. Chem. Res. 1978, 11, Chem. Soc., Faraday Trans. 1, 1973, 69, 776. 433. W. A. SEDDON, J. W. FLETCHERand R. CATTERALL, 27. M. A. J. RODGERS,J. Chem. Soc., Faraday Trans. l, Can. J. Chem. 1977, 55, 2017. 1972, 68, 1278. H. A. GILLIS, N. V. KLASSEN and R. J. WOODS, Can. 28. I. P. BELL, M. A. J. RODGERSand H. D. BORROWS,3". J. Chem. 1977, 55, 2022. Chem. Soc., Faraday Trans. I, 1977, 73, 315. G. R. FREEMAN,J. phys. Chem. 1973, 77, 7. 29. H. NORMANT,Angew. Chem. Int. Ed. 1967, 6, 1046. M. F. Fox and E. HAYON, J. Chem. Soc. Faraday 30. J. M. BROOKS and R. R. DEWALD, J. phys. Chem. Trans. 1, 1976, 72, 1990. 1968, 72, 2655. M. F. DEIGEN, Zh. Exp. Theor. Phys. U.S.S.R. 1954, 31. J. W. FLETCHER and W. A. SEDDON, Disc. Faraday 26, 300. Soc. 1977, 63, 18. D. A. COPELAND, N. R. KESTNER and J. JORTNER, J. 32. J. H. BAXENDALE,Can. J. Chem. 1977, 55, 1996. chem. Phys. 1970, 53, 1189.
absorptions is likely to c o m e from conductivity experiments, and from studies on mixed solvent systems. (3" It is worth noting that in pulse conductivity studies on binary alkane-demethylformamide systems, the results are consistent with an electron being captured by a single dimethylf o r m a m i d e molecule, although the interpretation is not unequivocal. (32)
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. l 1. 12.