2714
ELIITL- GOLDISH,
KENNETH HEDBERG ,4ND
1-01. 7s
1'ERXER SCIIOM.IKER
TABLE I11 FINALKESULTS LIMITSOF ACCEPTABILITY
WITH
STRUCTURAL PARAMETERS DETERMINED FROM qJq0 VAI.UES~ 7 . -
Parameter
FK3
F3
Q2
ICs
__Model KL3
KQa
EFI
I;;
~___~--_
EF3
QS
Result
C-F
1.346 1 . 3 3 4 1 . 3 3 8 1.343 1.339 1.343 1.333 1 337 1.333 1 . 3 1 2 1 31 =k 0 02 c-c 1.558 1.505 1.509 1.515 1.531 1 . 5 3 5 1.483 1.508 1.483 1 . 5 5 1 1 52 i . Or) c-0 1.376 1.401 1 408 1.414 1 402 1.414 1.443 1.447 1.408 1.413 1 . 4 1 f .Od LFCF 108.5' 108.5' 108.5' 108.5' 108.5' 108.5' 108.5° 108 5" 108 .io 108.t50 108 5 i 1 5" LCCO 107' 113' 111.5" 110' 110' 108.5" 111.5'' 110' 113' 107' 110 i -lo ri All values for interatomic distances are in Angstrom units. determined by this investigation are also included in this table.
the rotating sector12gave C-F = 1.334 f 0.005 and L F C F = 10S030' =k 30'; these values are in Discussion of Results close %greement with the microwave results13 oi An electron diffraction investjgation2 of CH3- 1.332 A. and 105O48',respectively. The studies in CHzOHgaveC-C = 1.55 f 0.02A., C-0 = 1.43 + this Laboratory of CF3CF33and CH3CF3*yielded 0.02 8., and L CCO = 110 i 3" ; these results are C-F = 1.330 i 0.015 and L F C P = 108.5 in cloge agreement with the values of 1.54 and 1.5' for CF3CF3,C-F = 1.33 =t0.02 A. and L F C F 1.43 A. for the C-C and C-0 distances, respec- = 108.5 f 1.5' for CH$F3. =1 determination of tively, obtained in an electron diffraction study2 of the structure of CF3C=CH1] by a combination of CHZCICHZOH. 1f3thin the limits of accuracy of the electron diffraction an$ microwave methods this investigation, the CCO angle is the same in CF3- gave C-F = 1.335 i 0.010 A. and L F C F = 107.5 CHIOH and CH3CHz0H. Unfortunately, the un- =k .'1 FCF angles less than tetrahedral have also certainties of the data do not permit an entirely been reported for CF3C=CCF314and CF3CN.'j I t valid comparison of the C-C and C-0 distances in is to be noted that the C-F distance is nearly the CF3CHzOH with these distances in ethanol and same in all these cases. ethylene chlorohydrin, but the results of this inAcknowledgments.-The authors wish to thank vestigation indicate that these distances are prob- Professor ITearian for the use of his electron difably shorter in CF3CH20H. Further, it appears fraction apparatus. They are als:, grateful to the that the C-C bond lengths in CF3CHz0H,CF3CF3 Purdue Research Foundation for financial support and CH3CF3 are very nearly the same (see Intro- of this work. duction). The values for the C-K bond distance and the LAFAYETTE, INDIASA (12) L. 0. Brockway, private communication. F C F angle (1.34 + 0.02 A. and 108.5 1.5', re(13) S. N. Ghosh, R. Trambarulo and W . Gordy, J . Chenz. Ph3.7, spectively) obtained in this investigation do not 605 (1932). differ significantly from the values reported for 20,(14) W. F. Sheehan and V. Schomaker. THISJOURNAL, 74, 4 4 M other molecules containing the CF3 group. A re- (1952). (1.5) A I . D . Danford and K. I.. Livingston, i b i d . , 77, 29-14 fIRR.5) cent electron diffraction study of CHF3 employing A%.
a.
[COSTRIBCTION
*
No. 2082, FROM THE GATESA N D CRELLIN LABORATORIES OF CHEMISTRY, CALIFORNIA IXSTITUTE O F TECHNOLOGY]
The Molecular Structure of Cyclobutene, C,H, BY
ELIHUGOLDISH, KEKXETH HEDBERG AND VERNERSCHO~IAKER RECEIVED FEBRUARY 6, 1956
The molecular structure of cyclobutene has been studied by electron diffraction in the gas phase. The bond dbtance and bond angle results for a molecule of CzVsymmetry are C-Cave = 1.537 f 0.010 fi., C=C = 1.325 f 0.04 A . and L C=C-C = 94.0 =!= 0.8"; the lengths of the two types of single bonds probably do not differ by more than 0.06 A. The bond lengths are discussed in connection with the possible effects of cross-ring repulsion, hyperconjugation, and angle stresses at the carbon atoms.
A considerable amount of structural evidence' indicates that carbon-carbon single bonds in threemembered rings are shorter, and in four-membersd rings are longer than the standard distance, 1.54 A. An explanation of the bond shortenings is suggested by Coulson and hloffitt's* treatment of bond angle strain, and Dunitz and Schomaker' have related the lengthenings to a plausible repulsion be(1) See J . D. Dunitz and V. Schomaker. J . Cham. P h y s . , 20, 1703 (1952). (2) C. A. Coulson and W .E . Sluliitt, i b i L , 1 6 , 151 (1911), Phil. ,WOE,, 40, 7th series, I ( 1 9 4 9 ) .
tween non-bonded carbon atoms. Cyclobutene, with its four-membered ring, seemed to us to be worthwhile subject for study in connection with these distance effects. The Structure Determination.-Samples of cyclobutene were kindly prepared for us by Drs. E. R. Buchman, J. C. Conly and I f r . Seville, by reduction of 1,2-dibromocyclobutane with zinc dust.3 Electron diffraction photographs were made both in the old apparatus4 and later in a newly con(3) J C Conly Thesis California Institute of Technolnji (4) I, 0 B r o c k u a \ , Rrr W u l e v n P h j s , 8 , 1 3 1 (1936)
1')in
MOLECULAR STRUCTURE OF CYCLOBUTENE
June 20, 1056
structed apparatus, and were interpreted5 by two of us independently. The work had been largely completed using the older data, but the much better newer plates enabled us to refine our results significantly. Theoretical intensity curves were calculated over the shape parameter ranges 0.837 6 C=C/C-C 6 0.889, 0.673 6 C-Have/C-Cave 0.752 and ~ 1 - - ~ c4I --c ~ +O.OS A. (see cut) for a -0.08
