March, 1963
COMMUNICATION TO THE EDITOR
part of the difference in the dipole moments of 1- and %substituted tetrazoles lies in the difference in the vectorial sums of the lone pair moments and the sigma bond moments, these moments more nearly canceling each other in the case of 2-substitution. A much smaller part of the difference is due to the reduced pi moment of the 2-substituted compounds. Although the accuracy of the calculated dipole moments does not warrant it, and although the existence of a tautomeric equilibrium between structures I and I1 has never been demonstrated, it is of interest to calculate an equilibrium constant between structures I and 11, if for no other reason than it is not known that this has ever been done before for tetrazole. It is found that, for a mixture of I and I1 to produce an apparent dipole moment of 5.11 D., K,, = [I]/[II]= 31.3, which corresponds to tetrazole existing as 97% in form I. Considering the probable numerical accuracy, this calculation may be considered consistent with tetrazole existing exclusively
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in the 1-protonated tautomer. This predominance of structure I is in agreement with the results of a recent n.m.r. study17 of the chemical shifts of the carbon bound proton on the tetrazole ring in tetrazole and N-alkylated tetrazoles. It is also consistent with the observation4 that 1-ethyltetrasole has a dipole moment of 5.64 while 2-ethyltetrazole has a moment of 2.64 D. Acknowledgment.-Thc author is indebted to Dr. P. G. Lykos of this Laboratory for suggesting this problem and for encouragement and advice during the study. The author wishes to thank Drs. It. L. Flurry and R. L. Miller of this Laboratory for many stimulating discussions, This work was carried out with a generous grant of computer time by the Illinois Institute of Technology. The author is especially indebted to the International Business Machines Corporation for a fellowship from the IBM Special Education Program. (17) 13. W. Moore and A . G. Whittaker, J . A m . Chem. Soc., 81, 5007 (1060).
COMMUNICATION TO THE EDITOR RELATIVE MOBILITIES O F LIKE-CHARGED IONS I N FUSED SALTSa
Sir: We wish to call attcntion to an observation, based on results of other workers as well as our own experimental data, that appears sufficiently general to warrant consideration in any attempt to understand the mechanism of ionic transport in fused salts. Our experiments were initiated in an effort to throw light on the reasons for the characteristic behavior of conductivity isotherms in fused salt mixtures. The equivalent conductance generally is found to deviate negatively from additivity of the pure salt values. l b Because this behavior is particularly striking in the case of LiC1-KC1 mixtures, we have been running Hittorf-type transference experiments to determine the relative mobilities of the two cations a t various concentrations. Electrolysis between chlorine electrodes is carried out in accordance with experimental procedures analogous to those described elsewhere for this type of experiment.2 By choosing the common ion (in this case chloride) as reference, we can use the results of such experiments t o compare the two cation m~bilities.~A useful quantity for this purpose is the per cent mobility difference 10O(pl3- p 2 3 ) / p 2 3which is equal to [100(4] - E1)/4,E1],and thus indepcndeiit of the conductivity of the mixture. Here El is the equivalent fraction of the faster-moving ion and 42 (= 1 - 41) is the quantity designated 4 by h i x aiid Wetmore.2b The latter quantity has been represented by P el~ewhere.~ (1) (a) This work is supported by a contract with the U. S. Atoiiiic Energy Commission. Financial assistance from a National Science Foundation pre-doctoral fellowship is also gratefully acknowIedged. (b) See, for example, R. W. Laity, J . Chem. Bduc., 39, 67 (l902), and references cited therein. (2) (a) A. IClemm, 11. IIintenberKer, and 1’. lioernes, Z. h’alur/uwch., 2% 245 (1947); (b) P. M. Aziz and F. E. W.Wctinoro, Can. J . Chem., 30, 770 (1952). (3) R. W.Laity, J . Chem. I’hyx., 30, 082 (1959); A n n . A’. Y . Acad. Sci.. 79, 997 (19GO).
Our preliminary results (described below) immediately recalled the corresponding observations of Duke and Victor4 on the system LiNOS-.KNO3, and prompted a search of the literature for all data indicative of relative mobilities of like-charged ions in binary fused salt mixtures. What follows is summary of our findings. Hittorf-type experiments have yielded the following results. LiC1-KC1.-At 2.2 mole per cent KCl Klemm and co-workers2a found the lithium ion more mobile than potassium by about 15%. Our results are in good agreement here, but are also consistent with the rather surprising observation of Chemla and coworkers5 on relative cation mobilities in the LiBr-KBr and NaBrKBr systems. These workers reported that in spite of the substantially highcr conductances of the pure salts LiBr and NaBr, I
