3040
Leon M. Dorfman and Bradley Bockrath
J. BELLONI.I would note an important point in polar media where we have difficulty getting experimental values of the mobilities of esalv-, the rate constant values of e- reactions give an indication of the mobility. In your case, if I remember, the maximum of esolv- spectrum is far away in the ir, despite the high static dielectric rate constants you observe for the decay in pure
DMSO.
A. M. KOULKES-PUJO.We correlated the high rate constant we observed to the solvation (or nonsolvation) of the electrons; an electron which absorbs in the ir, as you say, is less solvated so more reactive, so I agree with you. But I do not agree completely to a correlation of any anomaly between high dielectric constant and maximum absorptions of the solvated electrons. Other parameters have to be taken into account.
The Solvated Electron as Reducing Species in the Submicrosecond Formation of Reactive Transients. Carbanions in Solution Leon M. Dorfman" and Bradley Bockrath Department of Chemistry, The Ohio State University, Columbus, Ohio 43210 (Received July 23, 1975) Publication costs assisted by the U.S. Energy Research and Development Administration
The solvated electron, generated by pulse radiolysis, has proved to be extremely useful in fast reaction studies as the primary reducing species which forms organic intermediates of interest in other areas of chemistry. Organic free radicals1 have been generated by dissociative attachment to appropriate solutes in a variety of solvents. e,-
+ RC1-
R.
+ C1-
('1
Aromatic radical anions2 have been formed by nondissociative attachment to aromatic compounds. e,-
+A-
Am-
(2)
In the work we report here, carbanions have been generated3 by dissociative attachment to organomercury cornpounds in tetrahydrofuran.
-
+ RzHg
e,-
R-
+ RHg
(3)
In this way, the benzyl carbanion, PhCHZ-, has been formed and studied. It exhibits a uv absorption band with maximum a t 362 nm. Absolute rate constant^^^^ for its formation, as well as for the formation of (PhCHz-,Na+), in the following reactions, have been determined. e,-
+ (PhCH2)zHg
-
PhCH2-
-
+ PhCH2Hg.
(4)
k4 = 2.7 X 1O1O M-l sec-l PhCH2k5
+ Na+
PhCHZ-,Na+
(5)
= 1.5 X 10l1M-l sec-l
e,-
+ Na+
(Na+,e,-)
(6)
k s = 7.9 X 1011M-l sec-l
(Na+,e,-)
+ (PhCH&Hg k7
= 7.9 X
-
PhCH2-,Na+
lo9 M-l
sec-l
The Journal of Physical Chemistry, Vol. 79, No. 26, 1975
+ PhCH2Hg(7)
This is a convenient way of generating benzyl carbanion for fast reaction studies, and much information about its absolute reactivity has been obtained. The method may be extended to other carbanions5 and other solvents. Acknowledgment. This work was supported by the United States Energy Research and Development Administration. References and Notes (1)M. S.Matheson and L. M. Dorfman, J. Chem. Phys., 32, 1870 (1960). (2) L. M. Dorfman, Acc. Chem. Res., 3 , 224 (1970). (3)E. Bockrath and L. M. Dorfman, J. Am. Chem. SOC.,g6,5708(1974). (4)E. Bockrath and L. M. Dorfman, J. Phys. Chem., 77, 1002 (1973). (5)E. Bockrath and L. M. Dorfman, J. Am. Chem. soc., 97,3307(1975).
Discussion T. TUTTLE. While the stoichiometry of the species you identify as Na+,e,- is undoubtedly correct, in view of the very large shift in the optical spectrum attributed to the association, I wonder whether some more substantial interaction between the electron and Na+ is involved as for example in the solvated monomer. €3. BOCKRATH.It would seem that the question of the structure of the 890-nm band cannot be answered solely upon the basis of the magnitude of the shift of the absorption maximum observed upon association.
L. M. DORFMAN.The question to which you are drawing attention. the structure of the ion ~. Dair. involves the degree of interposition of solvent, Le., to what extent is it a solvent-separated ion pair? J. W. Fletcher's paper will likely deal with this, as will the comparison I shall make with other alkali metals, notably lithium. In our kinetic studies we refer only to the stoichiometry. J. W. FLETCHER.We have attempted to correlate the position of the absorption of Na+.e,- in T H F and other solvents with percent atomic character of the monomer as determined by ESR. This is considered in our paper.
