3045
NOTES
Since germanium is more electropositive than carbon, the simple inductive effect will oppose the .Ir-electronwithdrawing effect. Clearly, from the intensity changes, n-electron withdrawal predominates. Although the shift in energy of the 0-0 transition is not as definitive a criterion of n-bonding as is the variation in intensities,' the difference in frequency shown in Figure 2 between the 0-0 transition for anisole and that for p-methoxyphenylgermane is consistent with conjugative interaction by the germyl group. A comparison of the ratio of the oscillator strength of p-methoxyphenylsilane to the oscillator strength of anisole with the corresponding ratio for the germanium compound shows silicon to be more effective in 7rbonding than germanium
3 Frequency in
cm"
Figure 1. Ultraviolet spectrum of phenylgermane.
f(CH30C6H4SiH3) = 0.89l f(CHsOCeH5)
2400 2000
7
hfl
-
411 I I
From esr data and molecular orbital calculations,8 the n-bond orders for the silicon-carbon and germaniumcarbon bonds in substituted biphenyls are 0.18 and 0.13, respectively. The same relative n-bonding ability is indicated by the present investigation of ultraviolet spectra. Acknowledgments. This research was supported in part by the Advanced Research Projects Agency of the Department of Defense, through the Northwestern University Materials Research Center. One of the authors (J. M. M.) expresses appreciation for a predoctoral fellowship from the Division of General Medical Sciences, United States Public Health Service. The computer program was written by Mr. Louis Newman.
Frequency in cm-' Figure 2. Ultraviolet spectra of anisole (-) p-methoxyphenylgermane (- - - - - -).
and
Table I : Oscillator Strengths for Some Substituted Benzenes Oscillator strength, Compound
Anisole p-Methoxy phenylgermane Phenylgermane Phenylsilane p-Methoxyphenylsilane Phenyltrimethylgermane Phenyltrimethylsilane
1,4-Bis(trimethylgermyl)benzene 1,4-Bis(trimethylsily1)benzene Benzene a
x
(8) M. D. Curtis and A. L. Allred, J . Amer. Chem. Soc., 87, 2554 (1965).
108
20.95 20.0' 19.92 2.99 3.50" 17.75" 3.04 3.32 4.30 0.20 1.60'
Reaction Rate and Dissociation of Sulfuric Acid
by 0. Redlich and W. E. Gargrave Inorganic Materials Research Division, Lawrence Radiation Laboratory, and the Department of Chemical Engineering, University of Caldfornia, Berkeley, California 94780 (Received February 6 , 1968)
Reference 1.
Some time ago1 a kinetic study of the reaction known that the methoxy group is a n-electron donor, the germyl group must be a n-electron acceptor. The most feasible means of acting as a n-electron acceptor is through the use of the empty germanium 4d orbitals.
&So4
+ H20,
H2S05
+ HzO
led to the conclusion that the undissociated molecule (1) J. M. Monger and 0. Redlioh, J. Phys. Chem., 60, 797 (1956).
Volume 78, Number 8 August 1968
3046
NOTES The measurement of reaction rates may be useful as the third method of investigating the molecular state of strong electrolytes, in addition to Raman intensities and nuclear magnetic resonance. Acknowledgment. This work was supported by the United States Atomic Energy Commission under AEC Contract No. W-7405-eng-48.
C,,ld tmoles/liter 1
Figure 1. The acidity function, H,,logarithms of the activity, C ~ E ~ S Oand ~ , logarithms of the initial reaction rate: b, HzSOc (Monger and Redlich); 0, HzS04 (present work); 0,&SO4 (present work).
HzS04 is the intermediate between an instantaneous and a subsequent slow reaction. It is, of course, true that in a case of this type the kinetic formalism, based on activities, is the same for a trimolecular reaction of H+, HSOd-, and HzOz and for a bimolecular reaction of Hi304 and H2.02. However, a classical bimolecular reaction progress with a specific reaction rate increasing almost by lo6 for an increase of the sulfuric acid concentration from 5 to 12.5 mol/l. appeared to be so interesting that some further experimental support was considered desirable. The results are shown in Figure 1. The logarithms of the initial reaction rate with 1 mol of HzOz/l.a t 25.0" as found now are compared with the results of Monger and Redlich. The slope of the logarithm of the activity of sulfuric acid2 and the slope of the acidity functiona -Ho are also shown. The kinetic results (logarithmic slope value, 0.64) are in reasonable agreement with the slope of 0.71 of the activity. The acidity function with a slope of 0.52 between c = 5 and 12.5 fits the data less well. More recent data4 for Ho (slope = 0.58 between c = 9 and 12.5) would fit in the smaller range about as well as the activity. Results obtained in heavy solutions (D/(H D) = 0.86) agree within the experimental error limits with those from the light solutions. This result supports the assumption that the hydrogen ion is not rate controlling. (The activity function of D2S04 has the same values between c = 5 and 12.5 as HzS04.' Resultsa for DNOa indicate' that deuterium substitution does not appreciably change the strength of any strong acid.) Naturally one may call the variation of the initial rate by a factor of 106 a solvent effect. However, it appears to be preferable to avoid this term in an example which can be explained by a simple and perfectly reasonable model and to reserve the term "solvent effect" to cover those cases for which it has been invented, namely, where no simple model is applicable.
+
The Journal of Physical Chemistry
(2) (a) J. I. Gmitro and T. Vermeulen, A.1.Ch.E. J.,10, 740 (1964); (b) J. I. Gmitro and T. Vermeulen, Lawrence Radiation Laboratory Report UCRL-10886 (1963). (3) M. Paul and F. A. Long, Chem. Rev., 57, 1 (1967). (4) M. J. Jorgenson and D. R. Hartter, J . Amer. Chem. Soc., 85, 878 (1963). (6) E. Hogfeldt and J. Bigeleisen, ibid., 82, 16 (1960). (6) 0. Redlich, R. W. Duerst, and A. Merbach, to be submitted for publication. (7) G . N. Lewis and P. W. Schutz, J. Amer. Chem. Soc., 56, 1913 (1934); 0. Halpern, J. Chem. Phys., 3, 466 (1936).
Gas-Phase Far-Ultraviolet Absorption Spectrum of Hydrogen Bromide and Hydrogen Iodide'
by B. J. Huebert2 and R. M. Martin Department of Chemistry, University of California, Santa Barbara, California 08106 (Received February 18, 1068)
Quantitative data for the continuous absorption spectrum of HBr and H I are of interest for tho determination of excited-state potential energy curves and transition strengths, as well as for analytical applications.3~~ Extinction coefficients for these absorptions have been determined previously by photographic spectrophotometrya4,6 I n the course of photochemical studies with HBr and HI, we have measured th,e extinction coefficients for HBr from 2300 to 1700 A and for HI from 3000 to 1800 A, using a Cary 15 double-beam photometric spectrophotometer. The results are given in Table I and Figure 1, and comparisons wit,h previous data are shown in Table 11. HI was prepared from 55% aqueous hydriodic acid (Merck reagent grade) using standard vacuum techniques6 and was stored in the dark at - 196". HBr was prepared from 48% aqueous HBr (Mallinckrodt reagent grade) and was stored in the same way. Spectra were taken in an Aminco optical cell with Suprasil quartz: (1) Partial support of this work by a grant from the National ScienafP Foundation is gratefully acknowledged. (2). National Science Foundation Undergraduate Research Participant, 1966. (3) R. S. Mulliken, J . Chem. Phys., 8, 382 (1940). (4) J. Romand, Ann. P h m . (Paris), 4, 627 (1948). (6) (a) C. F. Goodeve and A. W. C. Taylor, Proc. Roy. XOC., A152, 221 (1936); (b) C. F. Goodeve and A. W. C. Taylor, ibicZ., A154, 181 (1936). (6) R. M. Martin and J. E. Willard, J. Chem. Phys., 40, 2999 (1964) a
