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VOLUME 71, NUMBER 6 MAY 15, 1967
The Hydrogen Resonance Spectrum of Cyclobutanone
by L. H. Sutcliffe and S. M. Walker Donnan Chemical Laboratories, The Uniuersity, Liverpool, England Accepted and Transmitted by The Faraday Society
(October 20, 1966)
The lH nmr spectra of cyclobutanone have been recorded at 40 and 56.4 Mcps and they have been analyzed on the assumption that the molecule comprises an AA‘BB’B‘IB”‘ (and not A 3 4 ) spin system. All the spectral parameters derived from the analysis are unexceptional apart from the rather large H-H cross-ring coupling constants.
The ‘H nmr spectrum of cyclobutanone recorded at 60 Mcps has been reported recently;’ unfortunately it was insufficiently resolved to allow proper analysis of the spectrum. In the analysis, Combs and Runnells’ assumed that the vicinal axial-axial and axial-equatorial coupling constants are equal and calculated the spectrum from the A2B4 spin system for JAB = 7.9 cps and AB = 1.05 ppm. The implication is that rapid interconversion between the two equivalent conformers of cyclobutanone causes the two coupling constants to become equal. However, a far-infrared study of cyclobutanone2suggests that the carbon skeleton of the molecule is planar since a ring-puckering frequency could not be found. Further evidence is that, even in asymmetrically substituted cyclobutanones, varying the temperature from -80 to +140° does not affect the spectrum;a also a deceptively simple spectrum is usually observed when a ring compound interconverts rapidly between two equivalent conformer^.^ These three facts imply that the molecule is planar, and it is unlikely that the axial-axial and axialequatorial coupling constants are equal in this situation. An AzB4 treatment therefore is incorrect, and this is confirmed by comparing the spectrum of Combs
and Runnells‘ with the experimental spectra in Figures 1 and 2 which show the low- and high-field parts, respectively, of the spectrum obtained in this laboratory at 56.4 Mcps under frequency sweep conditions. We have assumed planarity by analyzing the spectrum as originating from an AA’BB’B”B”’ spin system.
Experimental Section Spectra were recorded at 40 and 56.4 Mcps using a Varian HA-60 nmr spectrometer with a TMS locking signal. Cyclobutanone was purchased from the Aldrich Chemical Co., Inc., and was degassed thoroughly, An English Electric KDF 9 computer was used for the calculations.
Results and Discussion The calculated spectra shown in all the figures were ~
(1) L. L. Combs and L. K. Runnells, J. Chem. PhQS., 44, 2209 (1966). (2) J. R. Durig and R. C. Lord, ibid., 45, 61 (1966). (3) J. B. Lambert and J. D. Roberts, J . Am. Chem. SOC.,87, 3884 (1966).
(4) J. Feeney, L. H. Sutcliffe, and 9. M. Walker, TTUn8. Faraday SOC.,62, 2969 (1966).
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L. H. SUTCLIFFE AND S. M. WALKER
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obtained using a noniterative seven-spin computer program; trial values were used until a reasonable fit was found as shown in Table I. Table I
+To
L
170
140 cps from TMS
155
Figure 1. The low-field portion of the observed and calculated 1H spectrum a t 56.4 Mcps of neat cyclobutanone.
A’
Geminal coupling constants J A A= ~ -11.1 CPS J B B J= J B ~ J B ” ? -17.5
CPS
Vicinal coupling constants J A B = J A ~ =B JAB
125
115
105
CPS
CPS
85 cpa from TMS
Figure 2. The high-field portion of the observed and calculated 1H spectrum a t 56.4 Mcps of neat cyclobutanone. 90
80
70 cps from TMS
Figure 4. The high-field portion of the observed and calculated IH spectrum a t 40 Mcps of neat cyclobutanone.
The above values are within hO.2 cps of a perfect 8 A B = 1.05 ppm ( T A = 8.06 ppm and T B = 7.01 ppm). When an iterative computer program is adopted, then a better fit should be obtained.6 The hydrogen spectrum was recorded at 40 NIcps (see Figures 3 and 4) and computed for this radio frequency in order to check the uniqueness of the solution. In all the figures it can be seen that ringing has interfered with the experi-
fit for a chemical-shift difference,
~~
130
120
110 cp8 from TMS
Figure 3. The low-field portion of the observed and calculated ‘H spectrum at 40 Mcps of neat cyclobutanone.
The Journal of Physical Chemistry
( 5 ) While this work was in progress, B. Braillon and J. Barbet, Compt. Rend., 261, 1967 (1965),published a paper in which similar
spectral parameters were reported. A speotmm was not reproduced, however, and we are unable t o compare the accuracy of the fit with the present work.
INFLUENCE OF SU33STRATE STRUCTURE ON ADSORPTION
mental spectrum, and, the spurious peaks produced should not be confused with the real bands. A notable feature of the analysis is the rather large moduli of the cross-ring coupling constants; noninterconverting tetrasubstituted cyclobutanes6have a modulus of about 1 cps for this type of coupling. The constants are remaining in signs and magnitudes.
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Acknowledgments. We are indebted to the Science Research Council for providing an equipment grant. Also we wish to thank Mr. D. Collens of the University Computer Laboratory for his help.
(6)
C. H. Krauch, 5. Farid, and G . 0.Schenck, C h a . Ber., 99, 626
(1966).
The Influence of Substrate Structure on Adsorption. 11. Nitrogen and Benzene Adsorption on Characterized Silicas
by James W.Whalen Research Department, Field Research Laboratory, Mobil 02 Cbrporatwn, Dallas, Tezas (Received January 86,1966)
Precise gravimetric data extending down to 10" PIP0 have been obtained for nitrogen and benzene on two silica surfaces previously characterized by other techniques. When subjected to a BET treatment, such data provide a needed verification of constancy of nitrogen occupancy areas on surfaces of variable chemical composition. Relatively minor apparent surface area dependence on structure was found for nitrogen. Benzene does not form complete monolayers or statistically equivalent multilayers in the region of BET applicability. Interaction energy distributions derived for the adsorption processes occurring on representative surface structural states reflect interactions with oxide and hydroxyl surface domains. Variations in the form of the distribution function and the site interaction energies are consistent with surface structures and with the specific adsorbate interaction.
The Brunauer-EmmettrTeller (BET) isotherm equation in two-constant form
applied to the determination of surface area from nitrogen adsorption data has provided an indispensable basis for comparison of the surface properties of different substances in various states of subdivision and bulk structure. In such application the volume of adsorbed gas, V,, equivalent to monolayer coverage,
must be independent of the detailed structure of the surface. Variation in C (=exp(El - E L ) / R T )owing to variation in average first-layer adsorbate-adsorbent interaction energy (El) with surface structure must be accompanied by appropriate modification in the shape of the isotherm, ie., in the P - V , dependence. In particular it is required' that at monolayer coverage (J'alvrn = 1)
Volume 71 Number 6 May 1967 ~
