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3022
coupling constant as a function of spin density using Mclachlan spin densities gives a reasonably good linear relationship with slope = 23.2 The observed coupling constants correlate better with RlcLachlan spin densities than with spin densities calculated from simple HMO theory. On the basis of the esr spectra of five dianion radials, two of which contain nitrogen in the framework of the aromatic ring, we conclude that McConnell’s approximate equation for relating observed proton coupling constants with calculated spin densities on the attached carbon
AH =
(1)
QCH H PCH
can be applied to dianion radicals with &mHcv 23. The accuracy of this value will undoubtedly improve as the spectra of more dianion radicals are obtained. Theory predicts and esr spectra substantiate that very little spin density resides at carbon-9 of fluorene and 4,5-methylenephenanthrenedianion radicals. The smallest proton splitting in fluorene dianion radical is due to three approximately equivalent hydrogens. One of these hydrogens can be assigned to carbon-9 since this coupling is absent in 9-phenylfluorene. The latter has very little spin density located in the phenyl ring and no splitting from phenyl hydrogens is resolved. Nitrogen coupling in aromatic heterocyclic radical anions is proportional to the spin density located on the nitrogen atom and neighboring carbon atoms3
AN =
Q“PN
(2)
PC{
i
Table I: Hyperfine Coupling Constants of Dianion Radicals
X = CH
1.8
3.05
2.7
3.05
Position 3,6 4,5
0.35
4.53
--r
9
10,ll
0.35
X = C-CaHs
2.76
3.98
0.59
3.98
X = N
2.48
4.10
0.59
4.10
Y
3.02
0.53
3.02
0.36
3.00
0.51
3.00
o*60 5.08
= CH
Y = N
The Journal of Physical Chemistry
Acknowledgment. This work was supported by funds provided through the Director of General Research of the University of Georgia. (2) This value is in good agreement with the esr of cycloheptatrienide dianion radical: N. L. Bauld and M. S.Brown, J . Am. Chem. SOC.,87, 4390 (1965). (3) E. T. Strom, G. A. Russell, and R. Konaka, J . Chem. Phye, 42, 2033 (1965), and references therein. (4) E. W. Stone and A. H. Maki, ibid., 39, 1635 (1963).
DEPARTMENT OF CHEMISTRY EDWARD G. JANZEN THEUNIVERSITY OF GEORGIA J. GRADYPACIFICI ATHENS,GEORGIA JOHNL. GERLOCK RECEIVED JULY1, 1966
Pulse Radiolysis of the Aqueous Nitrate System. Formation of NO3 in Concentrated Solutions
N + CQci-.~
Carbazole dianion radical shows no nitrogen coupling. The calculated spin densities agree well with this observation since not only is the spin density on nitrogen essentially zero but the spin densities on neighboring carbon atoms bonded to nitrogen are also zero (0.007 and -0.0003 for PN and pc, respectively, Mclachlan calculations, X = 1.20, a = 1.5). For 4,5-iminophenanthrene dianion radical, the 0.60-gauss nitrogen splitting observed is in good agreement with
Dianion radical
0.58 gauss predicted from eq 2 if Q” = 30.9 and Qc-” = -2.0‘ (pn = -0.013, pc = 0.0432, McLachlan calculations, X = 1.20, a = 1.5). It is of interest to note that the spin densities and esr coupling constants of 4,5-methylenephenanthrene dianion radical are very similar to phenanthrene monanion radical. Similarly, 1,2-, 2,3-, and 3,4-benzofluorene dianion radicals can be described as substituted naphthalene anion radicals.
