Vol. 67
SOTES
940
Another significant effect is the increase of CHzO concentration when nitrogen oxides are present. According to the mechanism proposed by EnikolopyanQ to explain his studies of methane oxidation, the maximum CH20 concentration should be independent of the surface. It has been shown, however, that PbO coatings alone reduce the concentration of CH20. Results similar to these have been found in the oxidation of methane over potassium tetraborate surfaces using oxides of nitrogen as homogeneous catalysts (see for example ref. 10). These workers observed that in quartz and steel vessels without the coating the reaction is not reproducible when oxides of nitrogen are present. Furthermore, they find that the amount of formaldehyde produced is increased by coating the surfaces with K2B407. The increase of CH,O when nitrogen oxides and PbO are present can be explained in a t least two ways. (1) The PbO alone allom CHzO to decompose or to be oxidized without chain branching. The nitrogen oxides then simply increase the rate of formation of CH20. ( 2 ) The PbO, as has been suggested previously,ll removes species such as KO2or H:O, which lead to chain branching. The nitrogen oxides then furnish a route for the oxidation of methane without the usual necessary destruction of CH,O. The latter possibility seems very probable. As pointed out above, the CH20yield begins to drop when the surface-to-volume ratio becomes less than about 8. A previous report3 indicates that marked diff ereiices in the rate of reaction appear when the surface-to-volume ratio is increased to 8 cm.-' in uncoated vessels. The fact that the same critical ratio appears in the present work indicates that the same radical species is involved. It is felt that studies of the methane oxidation using PbO coatings and nitrogen oxides offer a valuable tool for obtaining further insight into the role played by surfaces. Acknowledgment.-The author is grateful to Mr. G. C. McCollum and Mr. R. NT.Thomas for assistance in carrying out these experiments. (9) N. S.Enikolopyan, "Sepenth Symposium (International) on Coiiibuslion," Butterworths Scientific Publications, London, 1959, p. 157. (10) N. S. Enikolopyan, et a1 , Zh. Prrklad Khsm., 32, 913 (1959) (11) D. E Cheaney, et al , "Seventh Symposium (International) uu Cotubustion," Butterm ortha Scientific Publications, London, 1959, p. 183
LOKG RANGE SPIN-SPIN SPLITTlNGS IS 4-VINYL I D E S E CYCLOPEKTESE BY MELVINW.HANNA AND J. KENKETH HARRIAGTON
where aHand aH' are the hyperfine coupliiig constants of protons H and H', respectively, and Aa(T) is the a-electron singlet-triplet transition energy. For the methyl-substituted allenes studied by Snyder and Roberts eq. 1predicts J14= 2.9 c.p.s. 4-Vinylidenecyclopentene (I) has recently been isolated in these Lab~rat~ories,~ and its n.m.r. spectrum is of
I L)=c=cIE2 .-
I interest in checking a more general application of eq. 1. The proton resonance peaks of interest are a triplet due to the allylic protons a t 6.877 and a quintet due to the vinylic protons at 5.407. The spin-spin splitting if 4.33 f 0.08 c.P.s., substantially larger than the long range splitting in the methyl a1lenes.l This larger splitting is of interest because of the basic structural difference between allene I and the allenes studied by Snyder and Roberts. I n the latter case the methyl groups are freely rotating and the average value of a E ' = 7 5 X lo6 C.P.S. was used in eq. 1 to calculate 14"'. I n alleiie 1the methylene protons have a fixed spatial orientation with respect to the 2-p orbital on the adjacent carbon. This allows a test of the more ge11,era1 equation for the hyperfine coupling of an H-C-C fragment. I n this case
a"
(S155 cos2 4 ) X IO6 c.p.s.
(2) where # is the angle between the H-C-c plane and the &-orbital axis.24 Assuming an HCH bond angle of logo, aH' is 99.4 X 106 C.P.S. Using this value in eq. 1 gives AHH'(a) = +5.4 c.p.s., ingood agreement with the observed value of 4.6 c.p.s. The important thing is that a larger splitting is predicted for allene I than for met hylallene. Acknowledgment.-Acknowledgment is made to the donors of the Petroleum Research Fund administered by the American Chemical Society and to the National Institutes of Health for partial support of this research. (d) S. J. Crista1 and J. K. Harnnxton, t o be published. (4) C. Heller and H. &I. McConnell, J . Chem. P I y s . , 32, 15.33 ( L W O ) , D. Pooley and D. H. Whiffen, M o l . Phys., 4, 81 (1961).
THERMODYNAMICS OF SILVER BROMATE SOLUBILITY I N PROTIUM AYD DEUTERIUM OXIDES1 B Y RICHARD W.RAMETTE b N D EDWARD A. DRATZ
Department of Chemssti y, Unavetszty of Colorado, Boulder, Colorado
Depaitment of C h e m t s t i y , Caileton College, X o r f h f i e l d , llznnesota
Recezved September 24, 1962
Recent experimental work by Snyder and Roberts has shown that in a large number of allenes and acetylenes the spin-spin splittings bet\\-een protons separated are between 2 and 3 c.p.s.l These by four carbons (J14) experimental results can be nicely correlated by Karplus' theory of a-electron coupling of nuclear spins. I n this theory the a-electron contribution to the spinis given approximately by spin splitting, &H'(n),
=
Rererbed October
4
1962
Except for studies of weak acid dissociation, w r y little attention has been given to ionic equilibria in deuterium oxide. One recent paper deals with oxalatocomplexes of cadmium and copper.2 Almost as soon as deuterium oxide was isolated it was discovered3 that sodium and barium chlorides are less soluble in this solvent than in ordinary water, and since that time a number of solubilities have been determined (1) From the Senior Thesis submitted by E A Dratz, Carleton College,
1961. (1) E. I. Snyder and J. D. Roberts, J . Am. Chem. Soc., 84, 1682 (1962). (2) M. Karplus, J . Chem. Phvs., 33, 1846 (1960).
(2) D L Moldasters ( t al. J Phys. Chem , 66, 219 (1962) (3) H Tajlor, E. Caley, and H Eyring J A m . Chem S a c , 66, 43.34
(1917)
