Research notes 1523

previous infrared study has shown that the covalent form can be trapped in the solid by deposi- t ion of the vapor onto a cold window at --185°C, and the irreversible change from the covalent form to the ionic form could be followed by recording the infrared spectrum as the sample warmed to room temperature [12]. With the low temperature Raman cell it is possible to carry out an analogous study of the Raman spectrum. PC15 was sublimed onto the sample rod at --135°C and the Raman spectrum recorded (Fig. 3). As the temperature was allowed to warm slightly above --135°C, changes in the spectrum were noted as disproportionation from the covalent PCI~ to the [PCla+] [PCla- ] ions occurred. The spectrum of the covalent form does show some weak lines due to the ionic form, and it appears that a temperature of --135°C is not quite low enough to completely prevent disproportionation. The assignments of the Raman frequencies have been discussed previously [12, 13].

SUMMARY

The cell described is simple in design, can be loaded in about ½ hr (including cooling), requires a min imum amount of sample, and is easily aligned in the Cary 81. I t does, however, require an instrument which employs the coaxial excitation optical arrangement.

Mellon Institute ~ERALD L, CARLSON Carnegie-Mellon University Pittsburgh, Pa. 15213

[12] G. L. CArSOn, Spectroehim. Aeta 19, 1291 (1963). [13] I. R. B~ATTIE, T. Gmso~, K. LIW~GSTO~, V. FAWC~-TT and G. A. Ozi~, J. Chem. See. A 712

(1967).

Spect~-~himica Acta, VoL 24A, pp. 1523 to 1526. Pergamon Press 1968. Printed in Northern I~land

The infrared and Raman spectra of cyclobutane-1, 3-dione*t

(Received 19 January 1968)

THIS note reports the first study of the vibrational spectrum of cyclobutane-1, 3-dione, which

H2 C

/ \ O ~ C C ~ O

\ / C H2

will be referred to hereafter as CBDO. I t was first prepared by WASSV.R~ and D ~ . o w [1]. The vibrational spectrum is of interest because there have been a number of recent investigations of other four-membered ring compounds concerned with (a) the planarity of the ring, and (b) the out-of-plane ring puckering vibration [2-9].

* This work was supported by the National Science Foundat ion under Grant GP-5050. From a thesis to be submitted by F. E. K. in partial fulfillment of the requirements for the

degree of Doctor of Philosophy at the University of Pittsburgh.

[1] I t . H. WASSERMA~ and E. V. D~.m~LOW, J. Am. Chem. Soc. 84, 3786 (1962). [2] K. FREI and H. H. G~ITHARD, J . Mol. Spectry 5, 218 (1960). [3] A. BAUDER, J. TA~K and H. It . GONTHARD, Helv. Chem. Acta 46, 1453 (1963). [4] J. B. L~.~IB~.RT and J. D. ROBERTS, ft. Am. Chem. Soc. 87, 3884 (1965). [5] C. Y. CHiN and R. J. W. LEF~.v~., Australian J. Chem. 18, 1293 (1965). [6] J. R. Dream, W. H. GI~E~.~ and N. C. HA~MO~rD, J . Phys. Chem. 70, 1989 (1966). [7] J. R. DuRIa and R. C. LORD, ] . Chem. Phys. 45, 61 (1966}. [8] T. R. BO~G~.RS and H. L. STRAUSS, ft. Chem. Phys. 45, 947 (1966). [9] W. G. ROTHSCHILD, J. Chem. Phys. 45, 3599 (1966).

1524 Resea rch notes

EXPE1%IMENTAL

CBDO crys ta ls were p repa red according to Refi [1]. Our samples h a d the same N M R s p e c t r u m (a single sharp peak a t 6.14 ~ in CDCla) and mel t ing behav ior (decomposi t ion to a r edd i sh liquid) r epo r t ed by these authors .

I n f r a r ed spec t ra were ob ta ined f rom 33 to 4000 cm -1 wi th B e c k m a n IR-11 and I R - 9 spect re- pho tome te r s . The vapor pressure of CBDO, which is less t h a n 1 to r r a t 20°C, is no t sumcien t to give an inf rared s p e c t r u m o f t h e vapor a t 8.2 m p a t h length. Solid CBDO was ex ami n ed as /qujol a n d ha loca rbon mulls. S a t u r a t ~ l solut ions in CCI4, CS 2, and CH2C12 were also used. Since all o f t he solut ions gave near ly ident ical spect ra , only the resul ts for CC14 are t abu la ted .

The R a m a n s p e c t r u m was ob t a ined for t h e solid only. S a t u r a t e d solut ions in ace tone , p-dioxane, CC14, CS2, and CH2CI 2 were too di lute t o give any da ta . A Cary model 81 R a m a n spec t ropho tome te r , modif ied for 6328 J~ exc i ta t ion wi th a H o - ~ o laser, was used. The Cary end -on i l luminat ion sy s t em for laser exc i ta t ion , employing a hemi-spher iea l lens, was used. The sample was con ta ined in a th in-waUed capi l lary tube which h a d one end sealed a n d pol ished fiat. The CBDO crystals were h a n d g round to a powder in a cold room a t 0°C, a n d the t u b e was

Table 1. Observed bands of cyclobutano-1, 3-dione (em -1)

Infrared * Raman Solid Satd. CC14 soln. Solid

3549 w 2970m 2960vw 2929m 2928m

2896 w, sh 2855w

2380w 2125vw 2091vw

1754 vs 1766 vs 1635w 1404 w 1361m 1342ra

1327s~ 1295m 1322 s J 1182s~ 1163 w, sh l176sJ 1164s 1156s 1042w lO16in 914 w 899w 848w

405w § 394m~ 382 s 388s ) 158 s § 98w 102w, br

2974

2919

1809

1343

914

637 547 443

*s, m, w = strong, medium, weak. v ~ very. s h = shoulder, br ~ broad.

Since all of the observed Raman lines are of ap- proximately equal intensity, no relative intensities are given.

No absorption was observed in saturated solutions of CCll, CS v and CH~OI 2.

§1~o absorption was observed in saturated OCI 4 solution.

Research notes 1525

t h e n filled be a dep th of a few m m wi th the powder. The l imi ta t ion to a powder and to end-on i l luminat ion m a d e i t impossible to ob ta in polar iza t ion data .

Table 1 gives the observed infrared and R a m a n frequencies. In f ra red frequencies are be l ieved to be accura te to ± 1 cm -1, R a m a n ones to + 2 cm -1.

~)ISCUSSIOI~ Point group

The results p rov ide convincing evidence for a center of s y m m e t r y in CBDO. There are no coincidences be tween observed infrared and R a m a n frequencies except for the 2970-2974 pair , and the 914-914 pair . I t is reasonable to a t t r i bu te the first pai r to two different C---H s t re tching fundamenta ls , and the weak 914 cm -1 infrared band to solid phase effects.

The presence o f a center o f s y m m e t r y requires t h a t t he r ing be planar . This was expec ted since eyelobutanone also has a p lanar r ing [3]. Nonp lana r i t y in eyclobutanes is due to repulsions be tween subs t i tuents on ad jacen t carbon atoms, and such repulsions are cer ta in ly smaller in CBDO t h a n in eyclobutanonc.

There are only two possible po in t groups t h a t are consistent wi th t he chemical s t ruc ture and a center of s y m m e t r y : C2h and D2a. C2a can be e l imina ted because i t requires t h a t t he r ing be a para l le logram wi th C - - C bonds 1 and 3 different f rom 2 and 4. This is unreasonable. Con- sequent ly , we adopt D2a symmet ry , a l though C2a cannot real ly be e l imina ted by our data .

Assignments

U n d e r Dsa s y m m e t r y the fundamenta l s of C B D O are classified as 5a a ~- 3bla ~- 2b2g ~- 2bsa (all Raman-ac t ive ) plus 4blu ~- 4bsu -b 3bsu (all infrared act ive) plus la u ( total ly inact ive) . F o r mos t of the observed frequencies i t is difficult to do more t h a n to divide t h e m into the g and u categories because we have no R a m a n polar izat ions or infrared contours of vapor phase bands to guide us. Most of the ass ignments would have to be based on analogy wi th o ther compounds such as eyclobutanone [2], d ike tene [10], beta-propiolactone [11], and the cyclobutyl halides [9, 12, 13]. W e do no t bel ieve t h a t these analogies provide an adequa te basis for the assignments, and therefore deem i t undesirable to express our guesses in Table 1. I t is possible, however , to be more definite about four of the observed bands.

1. Carbonyl stretches

One can be cer ta in t h a t the symmet r i c C ~ O s t re tch is a t 1809 cm -1, whereas t he anti- symmet r i c one is a t 1754 cm -1. A t first i t seems remarkab le t h a t t he symmet r i c one should be 55 cm -1 higher t h a n the an t i symmet r i c one since the opposi te is usual ly observed. (In CO S it is abou t 1000 cm -1 lower.) The reason for this is t h a t in CBDO, the values reflect no t only the work done to s t re tch the C~---O bonds hu t also t h a t done on the ring bonds. I t can be seen qua l i t a t ive ly (Fig. 1A) t h a t in the symmet r ic C ~ 0 s t re tch all the ring bonds are compressed. I n t he an t i symmet r i c C ~ 0 s t re tch (Fig. 1B) there is m u c h less work done on the ring, because

H2 H2 C C

/ \ / \ ~ ~O~-------C--+ ~C~---O ~ ~O~-------C ~ C~-------O

\ / \ / C C H 2 H~ A B

Fig. 1. Symmet r i c and an t i symmet r i c carbonyl stretches.

[10] J . R . ] ) ~ I G and J . W. WTT.T.T~J, JR., Spectrochim. Aeta P,~, 1299 (1966). [I1] J . R . D ~ m , Spectrochim. Acts 19, 1225 (1963). [12] J . R . ] )~x(~ and C. A. MORBISSEV, J. Chem. Phys. 46, 4854 {1967). [13] J . R . ])va~m and W. I-I. G ~ , J. Chem. Phys. 47, 673 (1967).

1526 Research notes

t he me thy lene carbons can rel ieve the force by m o v i n g to t he r ight . I t is therefore bel ievable t h a t the f requency is lower for the an t i symmet r i c mode.

2. t~ing puclcering vibration The out-of-plane r ing pucker ing v ib ra t ion is assigned to the weak infrared band a t 98 cm -1

in the solid and 102 cm -1 in solution. The hal f -wldth in solut ion is 36 cm -1. The s t rong infrared band in the solid a t 158 cm -1 is assigned to a la t t ice mode because this band is absent in solution.

S U ~ A R : e

The infrared spec t rum of cyelobutane-1, 3-diono has been ob ta ined f rom 33 to 4000 cm -1, toge ther w i th the R a m a n spec t rum of the solid. The d a t a are consis tent wi th Dua s y m m e t r y (planar symmetr ica l ring). The symmet r i c carbonyl s t re tch is 55 em -1 higher t han the anti- symmet r i c one. The out-of-plane ring pucker ing v ibra t ion is assigned to a band a t 98 cm -1 in t he solid and 102 em -1 in sa tu ra ted CC14 solution.

Acknowledgments---We are grateful to Prof. H . H . WASSERMAN for communica t ing to us details of the synthesis of CBDO not expl ic i t ly discussed in Ref. [1], and to Prof. S. D),mSHEFSXY for t he use of his ketone generator .

Department of Chemistry, University of Pittsburgh* and FoI/~ A. M-m~ER Mellon Institute, Pittsburgh, lPa. 15213 FR~.D E. K I V ~ T

I . M A T S U ~

* To which correspondence should be addressed.