SPECTRA AND STRUCTURE OF CF1=CH2
June 5 , 1957
[CONTRIBUTION FROM
THE
2691
DEPARTMENT OF CHEMISTRY, PURDUE UNIVERSITY]
The Microwave Spectra and Structure of CF,=CH,, CF,=CHD and CF2=CD2 BY WALTERF. EDGELL, PHILIPA. KINSEY'AND JONATHAN W. AMY RECEIVED OCTOBER 27, 1956 The K-band microwave spectra of CF~CHI,CFzCHD and CFzCD2 have been recorded and analyzed. With the assumptions that LHCH=DCD = 120' and ICD = I C E = 0.009 A., the following structural parameJers have been calculated: ICF = 1.321 zk O.O08Aii.,ICC = 1.31.1 f O.O08A., L F C F = 109' 15' i 25/, ~ C H= 1.10 & 0.05 A.
pointed Analysis of the Spectra; CF&H2.-As The structure of CFzCH2 is of interest since i t provides further information as to the changes in out by Roberts and Edgell12CFzCH2 is an oblate molecular configuration resulting from multiple slightly asymmetric rotor, and to account for the fluorine substitution in simple hydrocarbons. Such microwave spectrum the dipole must be along the information for the series of fluorinated methanes axis of the least moment of inertia. The two Q was summarized by Lidel; the carbon-halogen branch transitions which would be observed for bonds become progressively shorter as the number the limiting symmetric rotor each split into a series of lines as a result of the asymmetry. The band of fluorine substituents is increased. CFzCHz has previously been studied by micro- heads of these two sub-branches are near 26,700 wave spectroscopy2 and by electron d i f f r a ~ t i o n . ~mc., and one series extends to higher, one to lower It was felt that i t was worthwhile to repeat the frequencies. I n addition two R transitions should microwave investigation, since the frequencies be found in the region near these Q sub-branch were measured to an accuracy of only 3 mc. The band heads. The whole region should also be spectra of the deuterated species were studied t o covered with lines originating from high J transireduce the number of assumptions needed to calcu- tions, or from other Q sub-branches whose origins late the structure of the molecule. However, are outside the region of observation. An initial search of the region from 17,000 to with the data given here i t is still necessary t o assume a value for one of the structural parameters, 30,000 mc. yielded approximately 80 lines. Stark and for the extent to which the geometry of the patterns indicated that most of these lines had fairly high J-values. Analysis of the spectrum molecule is changed by isotopic substitution. essentially confirmed the assignments previously Experimental made.2 In addition the 202 --t 303 and 212 +. 313 The CFzCH2, CFzCHD and CFzCDz used in these ex- lines were found a t the frequencies predicted on the periments were part of the samples prepared by Edgell and basis of these assignments, and displayed the exUltee4 for the study of the infrared and Raman spectra. pected resolved Stark patterns. Table I gives the The purity of the CFzCDz and CFzCHD was checked by mass spectrographic analysis. The per cent. of CFzCHD calculated and observed frequencies of all identiThe observed but unidentified was 5.3%. The main impurity in CFzCHD fied transitions. in C F ~ C D Q was 294 of CFZCHZ. There was also evidence of about 0.470 lines for CFzCHz are listed in Table 11. The of CFzCDn. rotational constants are (in mc./sec.) (table). Observations were made with a Stark-effect sweep specCFzCDz.-More than 50 lines were found in the trometer of the Hughes-Wilson type6 using a 100 kc. square spectrum of CF2CD2 in the region from 19,000 to wave for modulation. Obsd.
A B C A = IC K
=
- ( I A - 18)
CFzCHi
11,000.8 10,428.8 5,345.6 0.234 0.79771
CFKHD
CFzCDr
Calcd.
Obsd.
Calcd.
Obsd.
11,000.8 10,429.5
10,926.9 9,545.5 6,086.7 0.262 0 52692
10,931.6 9,541.6
10,590.8 8,994.1 4,855.9 0 238 0 44326
......
The modulating voltages ranged up to about 800 practical volts. All measurements were made in a 10 f t . K-band wave guide absorption cell a t Dry Ice temperature. I N 2 6 crystal detectors were used and a Bendix radio range compass (ARN-7) was modified for use as a receiver. The sensitivity of the system was sufficient to detect n'H8 lines with an intensity of 1 X 10-7 cm.-I. Frequency measurements were made using harmonics from a UHF signal source6 which was calibrated by comparison with the standard frequencies broadcast by station WWV. It is felt that the frequencies given are accurate to f0.3mc., unless otherwise noted. (1) D. R. Lide, Jr., THIS JOWRNAL, 74, 3548 (1982). (2) A. Roberts and W. F. Edgell, J . Chem. Phys., 17, 742 (1950): P h y s Rev., 76, 178A (1950).
(3) I. L. Karle and J. Karle, J . Chcm. Phys., 18, 963 (1950). (4) W. F. Edgell and C. J. Ultee, ibid.. 22, 1984 (1954). (5) R.H.Hughes and E. B. Wilson, Jr., P h y s . Rcr., 71, 562 (1947). (6) The U H F signal source was designed and built by L. C . Hedrick, RCW.Sci. r w . , 24, 565 (1953).
......
Calcd
10.890.5 8,986.7
......
35,000 mc. Although i t was possible to calculate the general pattern of the spectrum from the assumed model, the great density of lines in the spectrum made an unambiguous assignment of individual transitions difficult. The analysis was greatly facilitated by the fact that the lol-+ 2,,? and 111-+ 212 lines could be identified on the basis of their Stark patterns. Table I shows the observed and calculated frequencies based on the rotational constants given above. CFpCHD.-About 80 lines were seen in the spectrum of CFzCHD in the region from 18,000 t u 36,000 mc. After identifying the lO1 202 transition on the basis of its Stark pattern, the analysis was completed by assignment of Q branch transitions. The observed and calculated frequencies + .
W. F. EDGELL, P. A. KINSEYAND J. W. AMY
2692
VOI.
79
TABLE I THEROTATIONAL TRANSITIONS OBSERVEDAND IDENTIFIED OF CF2CH2,CF,CHD
111 101
--
110
302
+
212
+
3 1 3 -t
303 312
-----
+
422
413 423
424 414 404 d33
523 524
+
+
212
202 211
303 313
312 322 331 441 432 422
432 424 423
532
542 523
55, 533 642 641 643 641 633 652 624 -.+ 643 53, 514
-+
+
---+
is:.
752
$43
762
AND
CF2CD2IN
MC./SEC.
CFzCHz
CF2CHD
CFrCDi
26,465.6(26,465.6)” 26,991.7(26,991.9) 36, 633b (36,632.0) 37, 461b (37,459.0) 37,417 (37,415.9) 26,646.2(26,646.2) 26,881.2(26,876.2) 18,075.0(18,078.6) 19,710.9(19,713.6) 27,014.7(27,010.8) 26,627.6(26,625.4) ....... ..
24,805.5(24,805.5) 25,912.7(25,912,7) 33,723.1(33,723.1) 35,751.8(35,751.8) 35,512.2(35,512.4) 24,595.1(24,598.0) 25,937.9(25,939.7) 21,056.0(21,057.1) 26,327.3(26,329.5) 26,815.7(26,818.4) 23,004.8(23,007.9) ................
23 ,561 .i(23,561 , 7) 24.778.2(24,778.2)
............... ................
................
Transition
25,725.2(25,724.3) 27,297.0(27,295.7) ................ ................ ................
25,245.7(25,245.9) 24,771.0(24,771.3) 27,821.2(27,819.9) ................
35,643.3(35,648.7) 20,529.2(20,529.4) 28,728.4(28,732.4) 34,704.2(37,707.7) 33,792.5(33,795.8) 35,643.3(35,648.8) ...............
32,264. 5(32,259.6) 35,922.1(35,924.4)
. . . . . . . . .
:14,liY.2(34,178.2) 33,857.0(33,856.8) 23,114.4(23,120.8) 24,950.7(24,955,4) 21,587.7(21,589.2) ................ .............
26,203.4(26,208.0) 33,619.5(33,628.4) ............... . . . . . . . . . . . . .
28,933. 9(28,938.0) 32,567.8(32,578.5) ................ ................
................ ................ ............... ............
23,435.7(23,440.2) ................ 28,696b (28,699.3) ................ ................ 744 743 ................ 30,801.8(30,812.~ J) ................ 863 862 21,745.2(21,749.2) ............... ........... Calculated frequencies are in parentheses. These lines are measured with an accuracy of =k 1 nic.
assumption can only be approximately true, i t seemed preferable to assume instead a value for 6, the shortening of the C-H distance with deuterium 24,357.4 26,329.0 17,OU8‘ 2 0 , 9 3 7 , l 23, 270a substitution. The value chosen was 0.009 8., in 17,229.3 21,484.0 23,323.11 24,449.6 26,335.6 agreement with the results of Miller, et al.,’ for the 17,843.8 21,572.6 23,360.4 24,543.3 26,726“ methyl halides; i t seems unlikely that 6 would 17,892.1 21,689.0 23,647.1 24,581.4 26,S32.0 differ from this value by more than a few thou18,907.5 22,236.3 23,770.5 24,639.8 27,112.0 sandths of an gngstrom. In these calculations it 19,098.9 22,273.4 23.814.4 24,729.2 27,218.6 is assumed that the HCH angle is near 120’ ; the 19,254’ 22.386.2 23,994. i 24,809.7 27,680.4 results are almost independent of the precise value. 19,660.9 22,394.8 21,020.5 25,352.1 28,177.7 rFF proves to be very insensitive to 6, changing 19,723.3 22,744.7 24,149.3 25,448.9 28,414.2 by only 0.002 A. if 6 is change$ from 0 to 0.009 A. 19,726.5 2~3,180.0 21,293.6 25,516.3 28,438.1 The best value Of ?‘FF is 2.154 A. 20,038.2 23,208.1 24,323.2 25,742.0 28,455.1 The r H H and r D D distances, of course, are more 20,34b.O 28,215.3 24,353 . R 26,116 ,1 28,945.3 sensitive to 8 t 0 for 6 = 0, YHHo= YDD = 1.881~A.; These lines were measured with an accuracy of 2~ 1 mc. for 6 = 0.009 A.,YHH = 1.912 A . , YDD = 1.897 A. The B moment of inertia of CFnCHzdepends on based on the rotational constants above are given three parameters which may be taken as the proin Table I. Structural Parameters.-For a planar molecule, jection of the C F distance on the CC axis, the C-C the moment of inertia about the axis perpendicular distance and the HCH angle. Although three to the plane should equal the sum of the other two isotopic species were available, the equation relatmoments. As a result of zero-point vibrations, ing the observed moment to these parameters for this holds only approximately for actual molecules; CF2CHD is nearly a linear combination of the corthe small value of the “defect”A = IC- (1.4- IB) responding equations for CFzCHz and CF2CD2, and given above confirms the assumed planarity of gives no additional information. It is therefore necessary to assume a value for one parameter in CF2CH2. The nioinent of inertia around the C-C bond in order to determine a structure. As a result of the small mass of the H atom, the CF2CH2 is a function of only two parameters: moment depends only slightly on any assumption Y F F , the distance between fluorine atoms and rHH, the distance between hydrogen atoms. With the made about the configuration of the CH2 group. assumption that the geometry of the molecule is If the HCH angle is chosen as 120’ for all isotopic unchanged by isotopic substitution one can calcu- species, and the isotope effect on the CH distance late 1’FF and Y ~ I Hdirectly from the A moments of (7) S L Miller, L C Admodt, L Dousmanis, C H 1 omnes a n d inertia for CF2CHz and CF2CD2. Since this Kraitchman, J Chem P h y s , 20, 1112 (1952) TABLE I1
OBSERVED BUT UNIDEXTIPIED LINESO F CFZCH2
Q
June 5, 1957
DISTRIBUTION OF SALICYLIC ACIDBETWEEN CYCLOHEXANE AND WATER
is the same as assumed above, the resulting parameters are those given below along with the results of the electron diffraction study.3 This research
