562
KOTES
Yol. 65
densing water vapor onto a metal mirror at -72” are “liquid hydrate” type crystals, since other researchers6’ who sought to repeat Rau’s results could do so only when they used water contaminated with organic compounds, such as ethyl alcohol. Although double hydrates of acetone with scme of the inert gases have bgen prepared,s giring cubic crystah with a = 17.3 A., this is the first time, SO far as we can find, that the acetone hydrate has been reported. Acknowledgment.-Ke are grateful to Dr. Richard K. 3fcMullan of the Crystallography Laboratory for his help with the X-ray diffraction studies. -1S.Q. wishes to thank the Kational Scieiice Foundation for financial support.
The situation is more complicated than, but not essentially different from, that which is possible in simple substituted ethanes, as pointed out by P ~ p l e . The ~ non-equivalence in question persists when a time average is performed over ail (nine) staggered (or eclipsed) rotational isomers. Phenomena of this type x\-hich depend on the energetic non-identity of rotational isomers have been reported by a number of investigators.6-8 However, it has perhaps not been adequately recognized that when the symmetry of substitution is sufficiently low, the non-equivalence of methylene protons can in principle still persist when the isomers are all accidentally of equal energy, or even when the internal rotation is free.5 (This statement depends entirely on a symmetry argument. ( 5 ) I T Rau, ScTlr Deut. d k a d Luft , 8 , 65 (1944) It seems unlikely that in practice the asymmetry ( 0 ) H \1 Chilong, J Glaciol 1, 5J (1947) with respect to internal rotation required to produce ( 7 ) 1 TV B i c x c r and 11. P Pdiner, Proc I’hys Soc 648,705 (1951) ( 6 ) J. Cr \Talle- haluie, 166, 129 (1960). magnetic non-equivalence n-ould not also be reflected in some angular dependence of potential energy.) IKTERPRE’rATIOX OF THE MAGKETIC If the phenomena observed by Finegold are to RESONANCE SPECTRUM OF THE be explained in this way, it is clearly not necessary METHk’LEK’E GROUP IN CERTAIN that the molecule coiitaiii two methylene groups. In fact, similar compounds containing only one tXlYNT6ETRICALLY SUBSTITUTED methylene group should give ‘‘iiormal” methylene COMPOUKDS resonances if Finegold’s interpretation is correct, BY J. S. WAUGHAND F. A. COTTON but should continue to shorn non-equivalences if our alternative description is valid. To decide Department of Chemistry and Laboratoru f o r Chemzcal and Solzd Stal, Phusics, Massach i s e t t s Institute of Technology, Cambridge, X a s s a between these possibilities, we have observed the chusetfs proton resonance spectrum of C6H5-S(O)-OCHaReceived Sooember 11, 1960 CH3,9 n-hich differs from diethyl sulfite only in Finegold has recently reported and commented replacement of one of the ethoxy groups by a on some apparently anomalous features of the phenyl group. The methylene resonance. shown methylene proton resonance in dialkyl sulfitesJ in Fig. 1, is readily recognized as attributable to a and in 0,0’-diethylmethylphosphonothioate,2 and pair of non-equivaleiit protons, in this case split similar peculiarities have been noted recently by to almost exactly the same extent by the methyl other investigators. These may conveniently protons. An analysis of the spectrum shons that be discussed with specific reference to the situation the chemical shift between these protons is 0.434 in diethyl sulfite. Instead of the 1:3:3:1 quartet i0.005 p.p.m. and the spin-spin coupling between expected for the splitting of the methylene reso- them is 10.0 f 0.5 c.p.s. Each of them is coupled nance by the adjacent methyl group, Finegold ob- to the methyl protons with a coupling constant of served h o such quartets, slightly displaced from 7.1 f 0.5 c.p.s. All the coupling constants are one another and showing slightly different cou- within the normal ranges’O l 1 for structures of this pling constants with the methyl group. That is, type. It is to be expected that the coupling coiione pair of methylene protons in the molecule is stants will be approximately the same as in diethyl clearly not equivalent to the other. Finegold sulfite, but the chemical shift between the made the natural assumption that each of these methylene protons is probably quite sensitive to pairs is in fact one of the methylene groups, and the substituents on the sulfur and may well be was thus forced to conclude that the two ethyl different. groups are ;,omehojv chemically different, Le., It is to be noted that a non-equivalence such as that thle two ,idfur-ethoxy bonds are differently Finegold proposed should lead to a simpler hybridized. methylene spectrum, inasmuch as the spin couWe feel it appropriate to point out that the above pling between non-equivalent hydrogens would be unipiiori is not necessary, and that an alterna- vanishingly small because of the large separation int crprel ation can be made and supported ( 3 ) J. A. Poplr, N o Z I’hys , 1 , 1 (1958) which does less violence to accepted theories of I’ XI Nair and J. 1) Rubeits. J . -In& C h t m S U L, 7 9 , 45b2 chemical bonding. I t simply involves the obser- (1957) J N Slioolrrs and B L Crauford J I J 1101 vation that the two methylene protons of thc 270(7)(1967). same methylene group are not stereochemically (8) 1). RI. Graliam and J. b \t augli, J Ciirm i ’ h 7 / 3 , 27, 9bb equivalent, because of the lack of symmetry of the (1957) (9) This coinpound %as hindly prepared by Llr 4 Blake folloning (non-planar) substituted sulfur atom with respect t o internal rotation about the S-0-C linkage. the procedure of R Otto a n d h Rossine Ber , 18, 2493 (1885) and was characterized b y C , H and S analsses. ((7)
(1) 1%.Iinezold, Proc. Chem. Soc.. 283 (1960) ( 2 ) H. Einegold, J. Am. Chem. Soc.. 82, 2641 (1900). (3) J. 1) Roherts ( t o be i>itblished). (-1) B. I hliailiro p l i r a t e communication.
(10) R. E Glirh and 4. A . B o t h e r - B y J (1956) (11) H
(1959).
C h ~ m I’hils
25, 382
S Gutoirsky h l Karplus and D R I Grant zhzd 31 1278
March, 19131
563
XOTES
DzO ISOTOPE EFFECTS I N THE CATALYTIC ACTIVATION OF MOLECULAR HYDROGEN BY METAL IONS BY J. F. HARROD AND J. HALPERS Department of Chemistry, The University of British Columbia, Vancouic r Canada Received December 2 f j 1960
With a view to gaining further insight into the role of t'he solvent in the catalytic activation of molecular hydrogen in solution,' t'he rates of reaction of hydrogen with a number of metal ions and complexes, in HzO and DzO, have been compared. Our results are summarized in Table I. TABLE
Metal ion
Fig. 1.
Rate law
1 Ternl,., OC.
kH20/ kD20
(10.1)
Ref.a
k[&] [Cu2+] 110 1.20 k[Hzl [Ag+12 50 1 23 Ag +* 75 1.26 k[Hzl &'+I Hg2 Hgz2+ k[Hz1[Hga2+l iJ 1.33 e Cu(0Ac)z k[H2][CU(OAC)~] 100 0.93 PdCLk[Hz] [PdCl,'-] 80 0.90 0 RhC1c3k[Hz] [RhC1e3-] 80 1.00 hLln04k[Hz][Mn04-] 50 0.99 Ag+ MnOd- k[H~][Bg+][hInO4-] 40 0.93 a Earlier measurements in HaO are described in the quoted reference. The same procedures were used in the present measurements and the results in HaO agree well with the earlier ones. While at higher temperatures, the reaction of Hz with Ag+ follows a rate law and mechanism siniilar to those for Cuz-, the predominant contribution under the conditions of this comparison is from the "termolecular" path which is believed to involve homolytic splitting of Hz according to equation 3 (ref. d, this Table). E. Peters and J. Halpern, J . Phys. Chem., 5 9 , 793 (1955) ; J. Halpern, E. R. Macgregor and E. Peters, ibid., 60, 1455 (1956). d A. H. Rebster and J. Halpern, ibid., 60, 280 (1956); 61, 1239, 1245 (1957). e G. J. Korinek and J. Halpern, ibid., 60, 285 (1956). E. Peters and J. Halpern, Can. J . Chenz., 33, 356 (1955). 0 J. Halpern, J. F. Harrod and P. E. Potter, ibid., 37, 1446 (1959). J. F. Harrod and J. Halpern, ibid., 37, 1933 (1959). A. H. Webster and J. Halpern, Trans. Faradall Soc., 33, 51 (1957). cu2+
+
of the proton pairs from one another. Thus it is a t first sight surprising that Finegold mould not have been forced into our interpretation by t'he complexity of his spectrum. Unfortunately, in diethyl sulfite, the chemical shift' seems accidentally to be so small that the additional lines are vanishingly weak, so that' the two possible kinds of nonequivalence are not readily distinguishable from one another. From his figure it would appear that the relevant chemical shift is in the vicinit'y of 0.05 p.p.m. If we assume the spiii-spin coupling between the non-equivalent protons to be 10 c.p.s., as it is in our compound, it) is easy to predict12 that the satellite lines should have intensities of only 1-2%; of t'he central components.1 3 Similar phenomena are observed in many other molecules.s,4 In diethyl acetal, for example, we have observed a complex met'hylene multiplet n-hich has been analyzed to give a chemical shift difference of 0.152 0.005 p.p.m., an internal spin coupling of 9.2 0.3 c.p.s., and couplings of about 6.7 and 7.2 C.P.S. between the non-equivalent methylene protons and the methyl group.'? It is significant that' the spectrum of ethylal, which differs from acet'al only in the substitution of a hydrogen atom for the central methyl group, contains a perfectly normal methylene quartet. l 4 This circumst'ance is completely in accord with the arguments preseiitcd here, since the ethylal molecule possesses too much symmetry to allow nonequivalence of thr protoiis in the same methylene group. We wish to thank ;he Sntioiial Science I-oundatioii for support of this work ( 1 2 ) J.
S.n ' a w l i . "1'rocerdin:rs of the IV International Meeting on
1H;Y. Perganion Press, London, in press. (13) I h . Finegold fpiivate communication) has agreed t o the probable correctness of the interpretation proposed here. He has stated that i n many other phosphorus compounds he had studied ( e . q . . (EtO)zP(O)Me. (F,t,O)zPMe. (ETO)zP(S)Cl, (EtO)zP(O)H a n d ( E t 0 ) z P i O ) S J I e all methylene protons appeared t o be equivalent a n d t h a t these obseryations caused him t o choose his previously published explanation for his observations on (ETO)zP(S)Me rather t h a n t h e one proposed here. (IS) C . S. Johnson. Jr.. J . P. Fackler, Jr.. J. S. Waugh a n d F. A . Cotton, unpublished work.
C F
'
+
J
It was hoped, in particular, that these measurements would provide a criterion for distinguishing those mechanisms2 in which Hz is split het'erolytically, transferring a proton to a water molecule, e.g. CU'+ -t HP
+ HzO +CuH+ + HaO"
(1)
from those in which a ligand other than water is believed to serve as the proton acceptor, e.g. Cil(OAc)z
+ Ha +CuH+ + HOAC+ OAC-
(2)
or in which H2is split homolytically without proton traii.qfer 2,4g+
+ Ha +2AgH+
3)
The results in Table I fail, however, to provide any clear-cut indication of such mechanist,ic differences. All the aquo ions included in the comparison (Cu2+, Ag+, Hg2+ and Hg2?+) shorn modest reductions in rate, ranging from 20 to 30%, on passing from HzO to D20, while the rates for complexes containing ligands other than water in (1) J. Halpern, J. P h y s . Chem., 68, 398 (1859): Aduances in Catalys i s , 9, 302 (1957); 11, 301 (1959). (2) Refs. r d Table I.
