2 10
NOTES I
I
I
I
I
I
I
I
I
I
I
IS-
-
W V
z a
m
LL 0 v) m
a
Figure 2. Resolution of thioacetamide-iodine ultraviolet spectrum in dichloromethane. (A) absorption of complex (corrected for free donor and acceptor), (B) extrapolation of major band (symmetrical with high energy side), (C) curve A minus curve B; concentrations in 1-cm cell a t 20”. Initial donor = 6.47 X lod6 M , initial iodine = 1.38 X 10-4 M , complex at equilibrium = 3.41 X 10-6 M .
in E for the shifted band may be off appreciably, considering the possible errors in the resolution. There is no question, however, that the intensity must be greatly increased because, for the concentration of donor used, the absorbance of the unperturbed n + a* transition would not be observable. The enhancement may be due to the transition being more allowed for the perturbed case, or intensity might be acquired from the mixing of states, particularly those of the weak intramolecular n + n* band and the highly intense intermolecular CT band.’ It should be pointed out that since both the C T and perturbed n --t T* bands are the result of the same complexation, calculations of thermodynamic values rereported in the literature from ultraviolet studies on related complexes still are valid. However, in those cases where the two bands overlap too closely, the emax calculated for the CT band may be high.
Aclcnowledgment. This work was supported in part by a grant from the National Science Foundation, GP6429. We wish to acknowledge helpful discussions with Dr. H. Hosoya and Professor S. Nagakura. (7) J. M. Murrell, J . Amer. Chem. SOC.,81,5037 (1959).
Nuclear Magnetic Resonance Spectral Correlation of Symmetrically Substituted 1,2-Diols and 1,3-Dioxalanes
by M. Gianni, J. Saavedra, R. Myhalylr, and I(.Wursthorn St. Michael’s College, Winooski Park, Vermont (Received J u l y 1 , 1969)
Ob404
I n a previous communication,l a method for an nmr structural correlation of symmetrically substituted The Journal of Physical Chemistry
epoxides and olefins was presented. The method depends on the observation of the chemical shift for the methine (C-H) hydrogen and requires that both cis and tmns isomers be available for comparison. I n the course of work on another problem, it became necessary to assign structures to a series of symmetrically substituted 1,Zglycols. Since only one isomer was available for some of these glycols, the previous method was not applicable. We now wish to report a method of unequivocal assignment of structure for disubstituted 1,2-glycols and l,&dioxalanes which obviates the necessity of observing the nmr spectra of both isomers. The synthetic sequence is illustrated below.
Previously, the best method of unequivocal structural assignment for the 1,2-glycols was optical resolution. The method is tedious and often difficult with tertiary alcohols. Dioxalane formation is easily accomplished and avoids difficulty with tertiary alcoho1s.2*3 The glycols are treated in benzene solvent with paraformaldehyde and catalytic amounts of p-toluenesulfonic acid employing a Dean-Stark apparatus for separation of the water from the reaction mixturen4 The nmr spectra of the dioxalanes are then used to scrutinize the methylene hydrogens. Dioxalanes of type 1 give an AB nmr spectrum due to the diastereotopic relationship5 of the methylene hydrogens. Dioxalanes of type 2 give an Az spectrum as a consequence of the enantiotopic relationship of the methylene hydrogens. Table I lists a series of such nmr values6 and the type of spectra observed. The nmr values for the methine hydrogens in the 1 ,&dioxalanes are consistent with the previous correlation rule: the methine hydrogen for the meso (cis) isomer absorbs at lower field than for the d,Z racemate (1) M.H.Gianni, E. L. Stogryn, and C. M. Orlando, J . Phys. Chem., 67, 1385 (1965). Summarized in this work were the cis and trans2,l-butanediol carbonates of F. A. Anet, J . Amer. Chem. Soc., 84, 747 (1962),and the cis and trans isomers of symmetrically substituted cyclic hydrocarbons of D. Curtin, Chem. Ind. (London) 1205 (1958). (2) This is a consequence of the mechanism of acetal formation; M. Kreevoy and R. W. Taft, J . Amer. Chem. Soc., 77,5590 (1955). (3) E. L. Eliel, ibid., 84, 2377 (1962). (4) The method of synthesis for all compounds reported is that of K. C. Branncock and G. Lappin, J . Org. Chem., 1366 (1956). All compounds gave satisfactory analytical data including ir and nmr. (5) For the terminology diastereotogic and enantiotopic as applied to these systems, see K. Mislow, “Topics in Stereochemistry,” Vol. I, John Wiley and Sons, New York, N.Y., 1967. (6) Caution must be exercised in extending the method t o conforma tionally mobile systems since a rapid inversion may cause the methylene hydrogens to give an AZspectrum due to averaging.
211
NOTES Table I : Hydrogen Chemical Shifts of Some Symmetrically Substituted l13-Dioxalanes
meso-4,5-Dimethyl dioxalane d,Z-4,5-Dimethyl dioxalane meso-4,5-Dipropenyl dioxalane d,Z-4,5-Dipropenyl dioxalane meso-4,5-Divinyl dioxalane d,L4,5-Divinyl dioxalane
TCHn
Type
5.3, 5.01 5.15 4.94, 5.20 5.08 4.85, 5.17 5.01
AB
Az AB Az AB
(8) Values determined from go and integration of the appropriate nmr peaks. Since the meso and d , l dioxalanes most probably form at different rates, care must be taken to ensure complete reaction for both isomers. (9) Observation of an AB spectrum reliably proves a meso form, but its absence cannot preclude a meso form due to the changes of accidental isochronicity. If accidental isochronicity is suspect, an aromatic solvent will usually serve to reveal the AB spectrum. (10) All spectra were run as 20% solution in CCla on a Varian A-60 spectrometer.
Az
(trans). The nmr values of the 1,2-glycols also indicate that the methine hydrogens for the meso isomer absorbs at lower field than for the d,Z racemate. This is in accordance with the findings of Wieman,’ who, however, notes that the tartaric acids are exceptions to the rule. The chemical shifts for the methine hydrogens for some 1,2-glycols and 1,3-dioxalanes are indicated in Table 11. Table I1 : Chemical Shifts of the Methine Hydrogen of Some Symmetrically Substituted 1,3-Glycols and 1,3-Dioxalanes
The Cobalt-60 7-Ray Radiolysis of Aqueous Solutions of Hz
G,,,-
+
Determination of
02.
+ GEIat pH 0.46-6.5l
by Knud Sehested, Hanne Corfitzen, Accelerator Department, Atomic Energy Commission Research Establishment Risp, Roskilde, Denmark
and Hugo Fricke Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60489 (Received J u n e 87, 1969)
TGH)
meso-Butane-3,4-diol d,l-Butane-3,4-diol
meso-3,4-Dihydroxy-1,5-hexadiene d,l-3,4-Dihydroxy-lJ5-hexadiene meso-4,5-Dihydroxy-2,6-octadiene d,l-4,5-Dihydroxy-2,6-octadiene meso-4,5-Dimethyl dioxalane d,l-4,5-Dimethyl dioxalane mes0-4~5-Dipropenyldioxalane d,Z-4,5-Dipropenyl dioxalane mes0-4~5-Divinyldioxalane d1L4,5-Divinyl dioxalane
6.30 6.50 5.94 6.20 6.00 6.20 6.01 6.60 5.75 6.18 5.60 6.08
It is important to note here that the concentration of each of the isomers in the diol mixture was reflected in the isomer ratio of the dioxalanes. For example, a 60/40 meso/d,l isomer mixture of the 3,4-dihydroxy1,bhexadiene gave the corresponding 60/40 meso/d,l isomer ratio of the dioxalanes.* Thus the mechanism as described by Kreevoy is valid for this reaction and no isomer scrambling occurred. The correlations for the methine hydrogens in the 1,2glycols and for the methine and methylene hydrogens in the 1,3-dioxalanes are internally consistant. One may therefore proceed with confidence when confronted with the problem of configuration when only one isomer of a 1,2-glycol or 1,3-dioxalane is a ~ a i l a b l e . ~ J ~
Recent determinations of the primary yields in aqueous solutions indicate that the previously reported value of G(H202) = 3.22a1b in y-irradiated neutral solutions of Hz Oz is too low. A similar G (peroxide) of 3.23 for the CHaCHzOH Oz system was recently explained by Bielski and Allen4 as due to an inhibitory effect of the reaction product CHsCHO. The present work shows that when the Hz O2 system is irradiated under conditions scavenging all the free radicals, G(H202)equals 3.66. Because of the simple nature of the reactions involved, this system would be expected to provide a reliable means of determining the yield of the reducing radicals. When OH in the irradiated H2 O2system reacts only with Hz, and eaq- and H only with Oz, the mechanism for the formation of HzOz is
+
+
+
+
OH
+ Hz
eaqH
“HOz”
+ Oz
+
-
---f
0 2
HzO
+H
(1)
02-
(2)
+HOz
(3)
+ “HOz” +HzOz +
0 2
(4)
“HOz” denotes the HOZ radical without regard to its state of ionization.
Acknowledgment. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research.
(1) Work performed in part under the auspices of the U. 5. Atomic Energy Commission. (2) (a) C. J. Hochanadel, J . Phys. Chem., 56, 587 (1952) : (b) N. F. Barr and A. 0. Allen, ibid., 63, 928 (1959). (3) A. Hummel and A. 0. Allen, Radiation Res., 17, 302 (1962). (4) B. H. J. Bielski and A. 0. Allen, I n t . J . Radiat. Phys. Chem., 1 ,
(7) J. Wieman and G . Dana, Comp. Rend., 258, 3724 (1964).
153 (1969).
Volume 74, Number 1 January 8, 1970
