NOTES
Feb., 1959
303
expected manner; the a-proton peak a t 5.24, 5.00 niid 5.71 7, respectively, shows an equal splitting 1'3: tlie X-H proton. This splitting varies from 5 t o 8 cyclewee.-' in the different compounds; it stnnds as proof t'hat proton exchange is excluded as a cause of tlie observed narrowing. These observations indicate that it niay be POSsible by such means to gain useful information concerning the electric fields surrounding various types of substituent groups. We thank George Filipovich for excellent iuninteiinnce atid opernt,iuii of the 1i.s.r. equipment.
C I P R O N O P Q T E ~ T I O n ~ ~ TSTUDY ~IC OF THE DISPROPORTIONATION OF U R AN Iu M (V) BY-R E I A U L LT. ) IWAXOTO K a n s a s , Lniurcirce, Kansas Recoiued J u l y 98,1958
Depai,li,ieiil of C ' i i e i n i s t r U , b'iiii'c!,situ of
1 2 3 4 5 G 7 S 0 10 shielding value, 7 (p.p.m.) Fig. 1.-Proton n.5.r. spectra of trifluoroacetic acid solutions (2O7,, wt./vol.) of: ( a ) N-acet31-DL-vctline; ( b ) glycyl-uL-tnethionine; (c) glycocyamine. -3-2-1
0
LCT.9.r.
N14compounds, the electric field a t the N14nucleus is evidently so honiogeneous that very little torque is exerted on the nucleus as the molecule rotates in solution. It appears possible in principle5p6 that a very narrow singlet N14-H proton n.s.r. peak should be observed even without proton exchange if the electric field a t the N14 nucleus can be made very inhoniogeneous by proper choice of structure. So far as me are aware, no n.6.r. spectral data have been reported for any compounds fulfilling this condition. As a part of a larger study, to be reported later, we have found that niany N-substituted amides, some closely related to those reported to give a broad N-H resoiiance, show this dramatic narrowing, giving 1i.s.r. peaks in trifluoroacetic acid solution having the relatively small apparent half-height widths of 6-10 cycles-sec. --I. Aniong these compounds are: N-acetylglycine, N-acetylDL-alanine, N-acetyl-DL-valiiie and N-acetyl-DLleucine; in acldition, iiinny (but not all) of tlie glycyl peptides of the coinnioii 0-amino acids, e.g., glycyl-~~-methionine,glycyl-m-serine, glycyl-m-threonine, g ~ ~ C ~ ~ - D L - ~ ~ and ~ l l icertaiii lle others. Guanidiiioacetic acid (glycocyamine) is an example of a compound which is not an amide but s h o w the effect clearly for the proton on the nitrogen bonded t o the methylene group. Figure 1 shows the spectra (obtained with a Variaii Ti4300-2 40.00 Mc-sec.-' n.s.r. spectrometer, tetramethylsilane as internal reference standard,' and a sweep of 220 mm. for 13 p.p.m.) of N-acetylDL-valine, glycy~-DL-niethionineand glycocyamine. The NH resonance a t 1.72, 2.05 and 3.14 7,respectively, is split by neighboring a-protons in the (6) J. A. Pople, Molecular Phys., 1, 108 (1QSS). 17) G. V. D . Tiers. T H I SJ O U R N A62, L , 1151 (1958).
Chronopoten tiometry, vol tammetry a t constant current, has been 11tilized successfully by Gierst and Juliardl-? and by Delahay and co-~vorker.s~-~~ for the evaluation of physico-chemical processes preceding and acconipaiiying dectrochemical reactions. This paper describes an extension of this technique for the evaluation of disproportionation reaction rate constants. The disproportionation of uraniiiin(V) has been investigated polarographically by a number of workers.ll-lY Among them, Orleniaiin and Kern14s'6 have obtaiiied experimental and calculated values for the disproportioiia,tioii rate constant. As with their theoretical approach, the reaction volume concept' has been followed in this paper. Experimental Reagents.-Reagent grade chemicals were used thoughout. The uranyl perchlorate solutioii 2.07 X 10-3 M was prepared by converting a weighed saniple of uranyl nitrate hexahydrate, through a double cvaporat,ion to dryness with pcrcliloric acid, to tlie perch1orat)e and diluting to a known volume with 0.4 111 perchloric acid. The p H of tlie solution was 0.83. Apparatus.--Siinilar electrical cquipinent' and cells have been described previously.l9 ( I ) L. G i e w t nntl A . J u l i n r d , Coinitt: iitt,ern. tlieriiiorlyriniii. e t c i d t . 6leetroehiiii.. Coiiii>t. rend., 2nd R & ~ n i o n .R l i l n l i , 117. 271) ( 1 9 a l ) . (2) L. Gierst and A . Julinrd, T H i b J O U R N A 57, L ,701 (1053). i3) P. Delnhny nnd T. Briains, J. A m . Cirtm. 8 o c . . 75, 2480 (1983). (4) T. Berzins and P. DCIRIIHJJ, ibid., 75, 4205 (1083). ( 5 ) P. Delnliny a n d C:. C. Rr:ltt:tx, i b i d . , 76, 87.4 (1034). ( l j ) P. Delnliay n n d C . C..\Inttnu, ibid., 78, 5314 11954). (7) .'I Drloliny, C. C'. A I a t t n x and 1'. Bcrzins, ibid., 76, 5310 ( I 034). ( 8 ) P.Deloliny and \V. !'klstich, i i i i d . , 77, 4!1.55 (19.55). (9) T. Berzins 2nd P. Dekihny, ibid., 77, ti448 (1955). (IO) P. Delnlinj,, Disc. F n r a d n ~Soc., 17, 205 (1054). (11) I. h1. I'hlthoff nnd W. E. Ilorris, J . Am. Cirern. S a c . , 67, 1.184 (l!l45). (12) I. 11. Iiolthoff and W. E. Hntwis. i b i d . , 6 8 , 1175 (1040). (13) €I. 0. Heal and J . Tlioinns, Trans. Faraday ~ o c . 45, , 11 (1040). (14) D. AI. €1. Kern and E. F. Orletiiann, J . Am. Chcm. Soc., 71, 2102 (1049). (16) I
