Proton Coupling Constants in CyclobutanoneL. L. Combs and L. K. Runnels Citation: The Journal of Chemical Physics 44, 2209 (1966); doi: 10.1063/1.1727010 View online: http://dx.doi.org/10.1063/1.1727010 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/44/5?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Calculation of nuclear spin–spin couplings. VIII. Vicinal proton–proton coupling constants in ethane J. Chem. Phys. 103, 6597 (1995); 10.1063/1.470388 Geminal ProtonProton Coupling Constant J. Chem. Phys. 43, 3402 (1965); 10.1063/1.1726410 Solvent Dependence of Geminal PhosphorusProton Coupling Constants in Benzylphosphonium Salts J. Chem. Phys. 41, 2570 (1964); 10.1063/1.1726321 Solvent Dependence of Proton—Proton Coupling Constants in Substituted Vinyl Silanes J. Chem. Phys. 40, 2415 (1964); 10.1063/1.1725531 LongRange Proton Coupling Constants in Vinyl Formate J. Chem. Phys. 36, 2235 (1962); 10.1063/1.1732867

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LETTERS TO THE EDITOR 2209

100,----

80

o GO -' '" ().

>= b. 0

'" i 0 0 l- ,0

340{).' o t" ........... A

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0'~----~2~0~----~4~0~----~G~0~----~

MOLE "10 NO

Fee. 1. Yields of HCl8N (1::.) and N18N+18NO (0) from reaction of l8N with various mixtures of CaB. and NO.

major volatile product. Dilution with excess of neon moderator produces little change, implying that hot and thermal reactions of N atoms with hydrocarbons are similar.

With HCN established as the major product of reac­tion with hydrocarbons, we inquire into the mechanism of its formation. Cyanide radical does not appear to be important as an intermediate since on reaction with ethylene it is known to yield a ratio of HCN/C2H3CN very different from that found.3 Similarly, NH is un­likely to be involved since plausible products of its addition to ethylene were not found.

It is likely that H03N is formed by direct addition of IBN to hydrocarbons, followed by decomposition of the resulting adduct. With excited N atoms this process is exoergic and spin allowed, e.g.,

CJI4+N(2D)~HCN+CH3' .1H= -117 kcal.

(1)

However, if the spin conservation rule is valid, similar reactions for quadruplet nitrogen are endoergic and not possible for thermal atoms.

C2H4+N(4S)~(quartet intermediate)

~HCN+:CH2+H AH=+40 kcal. (2)

It would therefore be expected that while N(2D) may react rapidly with hydrocarbons to form HCN, N(4S) could not do so and its eventual fate would be deter­mined by collision with an impurity or the wall.4

Evidence for this hypothesis was obtained on addi­tion of NO to the hydrocarbons (see Fig. 1). In the presence of only a few tenths percent NO, a large yield of Nl3N and 13NO appears while that of HCl3N dirnin-

ishes only slightly.6 This is precisely what would be expected from the presence of quadruplet nitrogen atoms, which cannot react efficiently with ethylene to form HC13N or any other product, but which do com­bine readily with NO. The presence of a second nitrogen species, which can react readily with ethylene as well as NO, is indicated by the fact that further increase in Nl3N and l3NO yields has an approximately linear dependence on the NO concentration.

We are grateful to the staffs of the Yale Heavy Ion and Electron Accelerators and to Maryan Marshall. These studies were supported by the U.S. Atomic En­ergy Commission.

• Department of Chemistry, Haverford College, Haverford, Pennsylvania.

t Present address: MIT, Cambridge, Massachusetts. 1 See for instance M. Marshall, C. MacKay, and R. Wolfgang,

J. Am. Chern. Soc. 86,4741 (1964). 2 (a) J. Dubrin, C. MacKay, and R. Wolfgang, J. Am. Chem.

Soc.86,4747 (1964); (b) J. Dubrin, C. MacKay, M. L. Pandow, and R. Wolfgang, J. Inorg. Nuc1. Chem. 26,2113 (1964).

a The properties of cyanide radicals as produced by free carbon atoms in the reactions

llC+N2-->llCN +N and llC+N20-->llCN +NO

have been studied.2b lICN produced by either of these processes reacts with ethylene to give a ratio of C2HaCN to HCN in the range of 4-7: 1.

• The recombination of N atoms is very unlikely in these sys­tems because of the low concentration of atoms. However, in active nitrogen systems it would be a major process as would radical-radical and atom-radical reactions.

i The usual interpretation of such a curve is that the easily scavenged species is a thermal atom, and the other is a hot atom. This is not the case here since the same general pattern of behavior is observed with thermalized N atoms.

Proton Coupling Constants in Cyclobutanone*

L. L. COMBS AND L. K. RUNNELS

Coates Chemical Laboratories, Louisiana State University Baton Rouge, Louisiana

(Received 15 September 1965)

THE purpose of this note is to report the absence of a measurable difference between the axial-axial

and axial-equitorial vicinal coupling constants in cyclo­butanone. Cyclobutanone is assumed to be a non­planar molecule with rapid flipping between the two possible conformations shown in Fig. 1. The following coupling constants are seen to be equal by the use of symmetry alone:

J 62 = J 64, J 62 = J 64, J61 = J63, J61 = J 63.

By considering the flipping to be sufficiently rapid to allow only average values of coupling constants to be observed, the following relations are implied:

JA = J 6l = J 62 = J 63 = J 64,

JE= J 62 = J61 = J64= J63.

The three remaining coupling constants are J 12 = J S4

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2210 LETTERS TO THE EDITOR

H5 H4

H6~4 =O~~3 H - H2

H2 H5 H =0 HI H6 I

FIG. 1. Ring flips in cyclobutanone.

and J 66• Indicating chemical shifts by 0 and assuming rapid flipping, Ih = 02 = 03 = 04 and 06 = 06.

For saturated six-membered rings axial-axial cou­pling constants (J A) are not in general equal to axial­equitorial coupling constants (J E) 1; there are numer­ous examples of considerable difference reported for the value of 1 J A - J E 1.2-6 To determine if this is also true for cyclobutanone, we have calculated the spec­trum assuming J A =J E using second-order perturba­tion theoryl and also using an exact method? based on the properties of angular-momentum operators which optimizes factoring of the secular determinant. The spectrum was then calculated by Louisiana State Uni­versity's IBM 7040 computer, varying the parameters until the best fit with the experimental spectrum was obtained, with the values Ih = 2.98 ppm relative to TMS, 05=1.93 ppm, J=7.9 cps. Under the assumption J A = J E, the coupling constants J 12 and J 66 are un­observable. These results are shown in Fig. 2. There is no great difference between the exact and the second-

6.0 7.0

FIG. 2. Proton spectrum of cyclobutanone. Top to bottom are second-order perturbation, exact, and experimental spectra. The weak absorption at about 7.6 'T is attributed to an impurity, also detected by gas chromatography.

order perturbation calculations, which would be ex­pected since the ratio of coupling constant to chemical shift is only 0.12. From the results shown in Fig. 2 it is clear that 1 J A - J E 1 must be considerably less than the values given in Refs. 2-6, surely less than 1 cps. This conclusion is in accord with previous findings about four-membered rings.s

The computer program was also used to calculate the proton spectrum of glutaric acid which has essen­tially the same symmetry. The agreement with the experimental spectrum was not as good as for cyclo­butanone, but good enough to conclude that the analog of 1 J A - J E 1 is probably no more than 1 cps.

The authors are grateful to A. T. Armstrong for obtaining the experimental spectra on LSU's Varian HR 60 spectrometer.

* This work was supported by a grant from Humble Oil and Refining Company, Baton Rouge, Louisiana.

1 J. A. Pople, W. G. Schneider, and H. J. Bernstein, High Resolution Nuclear Magnetic Resonance (McGraw· Hill Book Company, Inc., New York, 1959), p. 194.

2 J. Delmau and C. Barbier, J. Chern. Phys. 41, 1106 (1964). 3 A. Nickon, M. Castle, R. Harada, C. Berkoff, and R. Williams,

J. Am. Chern. Soc. 85,2185 (1963). 4 R. Lemieux, R. Kulling, H. Bernstein, and W. Schneider,

J. Am. Chern. Soc. 80,6098 (1958). 6 H. M. van Dort and Th. J. Sekuur, Tetrahederon Letters

20, 1301 (1963). 6 M. Karplus, J. Chern. Phys. 30, 11 (1959). 7 H. E. Dubb, L. Onsager, M. Saunders, and D. R. Whitman,

J. Chern. Phys. 32, 67 (1960). 8 L. M. Jackman, Applications of Nuclear Magnetic Resonance

Spectroscopy in Organic Chemistry (The Macmillan Company, New York, 1959).

EPR Studies of the Mo(CN)S3- and W(CN)g3- Ions. The Geometry of

the Ions ROBERT G. HAYES

Department of Chemistry, University of Notre Dame Notre Dame, Indiana

(Received 21 October 1965)

THE geometry of the ions M(CN)sZ, where M=Mo, W; Z=3-, 4-, has been in dispute recently. All

had been assumed to possess a dodecahedral geometry approximating D2d symmetry on the basis of a study of K4Mo(CN)go2H20 by Hoard and Nordsieck1 which revealed such a geometry for the Mo(CN)s4- ion in this crystal. More recently Stammreich and Sala2 have argued that the geometry of the free ions Mo(CN)s4-is that of the Archimedean antiprism, of symmetry D4d, on the basis of an infrared and Raman study. The optical spectra of all four species have been interpreted assuming both geometries.3.4

The magnetic parameters of a paramagnetic ion are often indicators of its structure. We have studied the electron paramagnetic resonance of Mo (CN)s3- and W(CN)S3- in glassy solutions in order to try to deduce the geometries of these species.

The electron paramagnetic resonance of both ions

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