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Microwave spectrum of s-trans acryloyl chloride
JOURNAL
OF MOLECULAR
Microwave R.
SPECTROSCOPY
Spectrum
of Chemistry,
(1972)
of s-Trans
D. C. HEXPHILL~
KEWLEY~,
Department
44, 443-458
AND
Rice University,
Acryloyl 3%.
Chloride’
F. CURL, JR.
Houston,
Texas 77001
The microwave spectrum of acryloyl chloride, H&CHCOCl, has been irivestigated in the S-40 GHz region. The spectra of the species H,CCHC03”Cl and HsCCHCOWI of the s-trans conformer have been assigned. The rotational constants and nuclear quadrupole coupling constants for the ground vibrational state are (in MHz): H&CHCOWl: A = 5546.24, B = 3821.10, C = 2262.07, xoo = 0.6, ebb = -24.4 and xcc = 23.8; H&CHCOWl: A = 5472.43, B = 3753.84, C = 2226.20, xaa = 0.3, XW, = -17.2 and xce = 16.9. The dipole moment components for H&CHCOWI are (in D) : p, = 2.76, ~6 = 1.45 and gtut = 3.12. The spectra of the first four excited vibrational states for torsional motion about the C-C bond have been assigned for the Wl isotopic species. From relative intensity measurements the torsional frequency is determined as 95 tlr: 25 cm-‘. Some lines which may be due to a secaond conformer (cis or possibly gauche) have been observed but not. yet assigned.
Acryloyl chloride, H&HCCOCl, is an example of an interesting type of molecule which may have two conformers related to each ot’her by rotation about a C-C single bond which is situated between conjugated double bonds. A number of molecules stru~turall~rsimilar t.o acryloyl chloride have been skdied by microwave spect,roscopists. Of these the most closely related are acroIein, for which only the s-trans form could be detected in a very careful investigation (1) and acryloyl fluoride (2). Both s-cis and s-trans forms of acryloyl fluoride were observed. From relat,ive intensity measurements the s-trans isomer was shown to be t,he more stable by 90 f 100 cal/mole, in good agreement with the value for AH of 150 f 100 caI/mole which was determined by studying the temperature variation of int,ensities of absorption bands in the infrared spectrum (3). In his electron diffraction study of acryloyl chloride, Ukaji (4) interpreted his results in terms of a predominant s-trans isomer together with a smaller propor1Acknowledgment is made to the donors of The Petroleum Research Fund, administered by the American Chemical Society, for support of this research. This work was also supported by grants from the National Science Foundation. 2 Present address: Department of Chemistry, Queen’s University, Kingston, Ontario, Canada. 3 Present address: Environmental Protect,ion Agency, Durham, N.C. 443 Copyright All rights
0
1972 by Aademic
of reproduction
in any
Press, form
Inc. reservzd.
44-l
KEWLEY,
HP:MPHILL,
.4X1) CURL
tion of a second conformer, assumed to bc the s-cis form. The structural paramc ters obtained were quite similar to the corresponding ones in acrolcin. The clearest evidence for the existence of two conformers is the infrared work of Iiaton and Feairheller (5) in which the trmpcraturc variation of rclativc intcn sities of the C-Cl stretching bands of t,he s-cis and s-trans conformers was invcst’igated and the s-trans form found to be the more stable by 0.6 kcal/molc. This figure indicates that at 25°C the concentration of t’hr s-cis form should hr al)out, one third of the s-trans form so that the microwave spectra of both conformers should be observable. Although there are indications in the present work t’hat the s-cis form is pres-, ent, the spectrum of that conformer has not yet been assigned. This report deals almost entirely with the rotational spectrum of s-trans acryloyl chloride. EXPERIMENTAL
Samples of acrylopl chloride were purchased from Aldrich Chemical Company Inc., Milwaukee, Wis. Although the substance is known to be moisture sensitive it was found satisfact’ory to use the samples without further purification. The samples were stored in t,he dark at -20°C. Acryloyl chloride changes from colorless to straw-colored after prolonged exposure to light at room temperatjurr. The initial work in the 7.5-26.5 GHz region was done with a conventional 100 kHz Stark modulation spectrometer with oscilloscope display, mostly at dry ice temperature. The 26.5-40.0 GHz region was observed with a Hewlett Packard 84608 spectrometer, mainly at room temperature. Samplr pressures in the range 5-30 Mmwere employed. The accuracy of measurrmcnt for the Hcwlctt Packard spectrometer is in t,he range ho.01 to +0.05 MHz wherea,s for t,hc 100 kHz Stark modulation instrument the accuracy is about f0.3 :\lHz. ROTATIONAL
SPECTRUM
Approximate calculations from assumed structures predicted that the s-trans form should be highly asymmetric with K in the range 0.3 to -0.2 and that, the s-cis form should be a slightly asymmetric top with K in the range -0.8 to -0.9. Both conformers should have observable u-type and b-type t#ransitions. The observed 7.5-26.5 GHz spectrum nas found to be a, very rich one, complicated by the nuclear quadrupole splitting due t,o the chlorine atom. An initial assignment of the transition 2pl + 313 was made from the Stark effect. ,4 number of other low J lines were similarly assigned allowing approximat)e rotational constants of s-trans H,CCHC035Cl to be determined. However, attempts to assign the individual nuclear quadrupolc hyperfine components of these low ./ transitions proved unsuccessful on account of the extra and unrelated lines usuall> found near or within a hypcrfine pat’tern. The approximate rotational constants were confirmed by prediction and sub-
MICROWAVE
SPECTRUM
OF s-TRANS
HzCCHCOCl
445
sequent observation of higher J transitions in the 26.540.0 GHz range. The transitions found were mostly of the type ‘Ro, 1 although a few bR1,l and bR_l,l lines were also recorded. The intensities in the group of lines 616---f 7,,, , t& + TIT, 606+ 707and 606-+ 717which falls between 33930 and 33940 MHz (see Table I) allowed the ratio ~02/~2 to be estimated at about 3, which later helped in the assignment of Stark lobes. The characteristic pattern of this group also greatly facilitated the assignment of the corresponding set of lines for t,he HzCCHC037C1 species (see Table II). In addition, four set’s of vibrational satellites of H&CHC035C1 were assigned. (ii) Analysis
of ,Vuclear Quadrupole HyperJine Structure
Because of the difficulty of assigning quadrupole components for the low J lines and because of the much better accuracy of measurement in the 26.5-40.0 GHz region, it was decided to rely on the measurements in the higher frequency range to determine quadrupole coupling constants. For the H&CHC035C1 species in the ground vibrational state well resolved quartets were found for the six transitions 413+ 514, -I40-+ h , 514+ 615, 523 -+ 624, lidI--+ 6~ and 5~ + 6j1 . The 514-+ 616transition is shown in Fig. 1. For these six transitions it was found that the pressure had to be less than 10 pm to achieve satisfactory resolution of the members of each of the two closely spaced doublets. This naturally resulted in a rather poor signal-to-noise ratio (about 15: 1 for 514+ tj15). However, the frequencies of the four components could still be measured with a reproducibility of bett’er than ho.05 MHz. A least-squares fit was performed for the twenty-four quadrupole components to give the six unpert,urbed line frequencies and the values of the coupling constants xaa and xcc. The coefficients dv/c?x,a an d dv/dxcc for the least-squares fit were calculated from the equation W, =
Y(F)/J(J
+ 1) [{J(J + 1) + E(K) - (K + 3wm.~Xaa f (J(J + 1) - E’b) + (K - 3&wwd
(1)
The standard deviation of the fit was 0.03 MHz. The st’andard error for each of the six line frequencies from this treatment was given as 0.02 MHz. The resulting coupling constants are in Table III, Xbbbeing determined by the rela0. The uncertainties quoted are the standard deviations tion %% + Xbb + estimated from the statistical analysis of the least-squares procedure. The transitions in which the hyperfine splitting depends most strongly on xaa have the larger values of K1 and so are the weakest for a given J --, J + 1. It was not possible to obtain satisfactory resolution of such transitions for other than the ground vibrational state of HzCCHC035C1. For the weaker absorption peaks of the first and second excited torsional states of HCCHC035C1 and for the ground vibrat,ional state of H&CHC037C1 a slightly different method of xc0
=
KEWLEY,
446
HEMPHILL, TABLE
AXD
CURL
I
OBSERVED FREQUENCIES OF R-TRANS ACRYLOVL CHLORIDE, H?CCHC0”5CI, IN GROUKU AND EXCITED TORSION \I, STATES
10, --f 2%
‘L,?4 313
2z1 + 32.’ 211 + 322
321 --j 422
41s --f 514”
423 ---f 521
422 ---f 5%
432 + 5% la, + 5,,
4 41 ---f 542
3/2 5/2 l/2 312 l/2 512 T/2
---f + + + ---f + --f
gs. 5/2 7/2 l/2 5/2 3/2 712 9/2
5/2 --f 712 3/2 ---f 5/2 7/2 ---f 9/2 l/2 9/2 3/2 7/2
7=1
23 425.60
+ + ---) ---) + + +
7/2 11/2 9/2 13/2 7/2 11/2 9/2
w2 5/2 9/2 712
+ + + ---f
1312 712 11/2 912
34 042.29
lu2 5/2 4
7/2 1312
34 043.08
5/2 11/2 7/2 9/2 5/2 1112
7/2 13/2 912 II/2 7/2 13/2
23 431.47 27 579.4ti
31 904.16
31 817.13
9/2 11/a
31 905.36
31 818.24
7/2 13/2 9/2 11/2
32 32 32 32
27 3’2t2.48”
27 579.86 27 29 29 29 29
580.37 980.00 980.66 982.66 983.51
28 926.82 28 927,87 ’
31 380.79”
+ + --) --)
7=4
15 548.58 18 250.00* 23 121.23
5/2 9/2 7/2 11/2 512 912 7/2
5/2 11/2 7.0 9/2
7=3
15 547.56
3/2 11/2 5/2 9/2
+ + ---) ---f + +
7=2
11 482.83 11 185.47 11 GB.18 15 546.57
4 + +
712 + 9/2 + 440 + 541”
vo~,aci(MHz)
F F’
Transition
280.09 280.53 282.04 282.52
28 908.86
28 887.33
28 862.87
28 8:Qi.41
28 909.88
28 888.39
28 864.03
28I837.54
33 894.41&
33 816.84%
31 250.98”
31 182.71a
31 317.03” 33 90G.94
33 637 .03
33 908.73
33 638.72 31 637.69a
31 112.788
MICROWAVE
SPECTRUM TABLE
Transition
515 4
5 15 -+
50~ +
50 +
514 -+
513 4
9/2 11/2 7/2 13/2 616 9/2 11/2 7/2 13/2 60s 9/2 11/2 7/2 13/2 610 9/2 11/2 7/2 13/2 61j” 11/2 9/2 13/2 7/2 624b 11/2 9/2 13/2 7/2
524 + h5
5 33 --t h4
541 -+ 64~~
5rz ---f 643
5ao + 6~~
H,CCHCOCl
I-Contin~d
7=1
g.s.
--f 11/2 + 13/2 + 9/2 + 15/2 4 11/2 + 13/2 ---t 9/2 + 15/2 4 11/2 + 13/2 ---t 9/2 + 15/2 + 1112 + 13/2 + 9!2 -+ 15/2 --f 13/2 + 11/2 + 15/2 + 9/2 ---f 13/2 + 1112 --i 15/2 + 9/2
29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 34 34 34 34 39 39 39 39
397.63 397.82 398.14 398.32 403.19 403.36 403.66 403.98 420.36 420.58 420.88 421.11 426.07 426.19 426.47 426.66 231.00 231.36 232.85 233.23 478.87 479.58 480.89 481.58
1112 + 9/2 +
1312 11/2
33 767,87
‘;;;
$
29 29 29 29
7=2
7=3
29 448.07*
29 4l39.19a
34 34 34 34 39 39 39 39
34 34 34 34 39 39 39 39
244.48 244.83 246.42 246.74 442.91 443.60 444.85 445.50
29 485.50a
33 739.18
33 768.98
33 763.62
33 753.65
33 740.26
11/2 9/2 ---f + 1112 1312
37 og4, l4
37 038.31
36 979.22
13’2 7/2 ---f ----)912 15’2
37 094.58
37 038.79
36 979.60
7/2 13/2 9/2 1112 7/2 13/2
9/2 15/2 11/2 13/2 9/2 15/2
39 39 39 39
38 408.93
39 309.47
11/2 g’2 +
1l’2 13/2
38 409.45
39 309.98
7/2 13/2 9/2 11/2
9/2 15/2 11/2 13/2
38 38 38 38
+ + --t +
771.52 771.79 773.48 773.80
430.26 430.50 431.72 431.94
29 498.42a
254.44 254.72 256.37 256.79 403.78 404.26 405.49 406.07
33 752.56
+ + --t + + +
7=4
429.48 429.64 429.97 430.16
33 762.57
7
447
yot,sd (MHz)
F F’
606
OF s-TRANS
36 917.50”
36 852.84a
39 292.84
39 133.30
39 294.76
39 135.22
38 103.948
448
KEWLEY,
HEMPHILL,
.4NU CURL
TABLE I-Continued Transition
G16--) 701 (i*F,4 7,i (i”6 + 707 6°C 4 711 cil:, ---tii, 13/2 --t 11/2 + 15/2 1312
GI:,-
7~
701 - 80s 7Ii ---f 818 SD UC
~oi,-d(MHz)
F F’
7=
5s
33 33 . 33 33
93l.lV 912.4V t 936.7V 938.0-P
1
33 96-l. 17a 33 965.55* 33 97o.ooa
7=4
34 010.54~ 34 026.31~ 34 015.96* 34 032.08”
38 598. O’LL 38 528, 84a 38 496. 90a 38 527.60” 0.14 0 l(i
38.553.138 38 572.w 38 551.78* 38 570.69” 0.14 0.20
38 595.74
15/2 ---) 1712 912 + 11/2 38 581.60
38 596.96
13/2 + 1112 + 15/2 1312 38 11g.78
38 425.71
15/2 9/2 + 4 1712 11/2 38 -J20.76
38 426.70
_
7=3
33 991.01a 33 995.90a 33 997.53’
38 580,14
38 158. 31ja 38 157.333 0.20
T=2
* No qultdrupole structure was resolved. b Transition used in 35C1quadrupole analysis, gro\uld state. c For least-squares fit, to rotational constants. analysis was used.
In these cases all observed yuadrupole component’s, including poorly resolved quartets and mcmbcrs of doublets, w-erc used in least-squares fitting. When two strong quadrupolc: components are observed as a single peak the coefficients of xaa and xcc for each component were calculated. An average coefficient
for each of xaa and xcc was then calculated,
of the two components
in proportion
to their calculated
weighting
the coefficients
intensities.
It may be seen from Table III that thr values of xaa, Xbband xECfor the first and second excited torsional states agree wit’h the values for the ground &ate within experimental error. The ground state coupling constants are more accurate, however. The element xcc corresponds t’o a principal value xrr of the quad-rupole tensor. The observed xcc for H2CCHC05’Cl should thcrcforc bc lower than xcc for H$2CHC035C1 by a factor QzT/Qsj= l/1.26%. A value of 23.S/1.26%S = IS.8 f 0.2 MHz is expectctd for xec compared t)o the experimcnt’al value of 16.9 + 0.4 MHz. One part’ial explanation of the discrepancy may be that’ as overlapping of adjacent lines becomes mow pronounced the observed hyperfine splittings are less than would be found if line widths wtre negligible so that, coupling con stants will tend to appear lower than the true values. Direct comparisons cannot be made for xoa and Xbbof the “‘Cl and 37C1 species because of tht: rotation 06 principal axes on isotopic substitution. Quadrupole analysis was not attempted for the higher excited states because of insufficiency of data.
MICROWAVE
Sl?ECTRUM TABLE
OBSERVED
FREQUENCIES
Transition 413 ---t 514
413 +
5%
432 --f 5a3 4 (0 + 541
F E’ Q/2 7/z 11/2 5/2 Q/2 7/2 11/Z 5/a 5/z II/2 7/2 Q/2
51: + 6”s 51: --t 61s 505 ---f 606 505 --f 616 514 + 615
1312 7/2 11/Z 5% + 6% Q/2 L3/2 712 St. dev. (r = 0.25 8 No quadrupole
--) --) + --) + -+ + -+ + -+ +
-+ ---t --t t + --t
7/‘2 13/z Q/2 11/a
1512 Q/Z 13,‘2 llj2 15/Z 9/z
HzCCHCOCl
449
II
OF S-TRANS ACRYLOYL CHLORIDE, H~CCHCO~CI, GROUND VIBR.%TION~L STATE Vobsd(MHZ)
11/2 Q/2 1312 7/2 U/2 Q/2 13/Z ?/2
OF s-TRANS
29 29 29 29
513.62 514.27 515.45 516.09
28 455.58 28 456.33 30 31 31 31 31 28 28 28 28 33 33 38 38 38 38
845.538 701.11 701.56 702.58 702.80 931.22” 936.86~ 954.76% 961.13% 699.21 699.56 846.12 846.62 847.56 848.05
Transition
F P’ 11/2 9/2 13,/Z ?/2 11/2 Q/2 13/2 7/z
-+ -+ -+ ---t --f -+ --, +
m.d(MHZ) 13/2 11/2 15/2 Q/2 1312 11/2 15/2 9/z
33 225.82 33 226.65 36 474.14 36 474.61 33 392.84” 33 394.40% 33 398.86*
13/2 U/2 15/2 Q/2 13/Z U/2 15/Z Q/2
3 -+ ---f + -+ -+ -3 --+
15/2 13/2 I?/2 11/Z 15/2 13/2 1712 11/z
37 973.94 37 974.69 37 807.99 37 808.71 37 848.56” 37 847.3P
st,ructure was resolved.
The quadrupole analysis for the ground vibrational state of H&CHC035C1 yielded the unperturbed frequencies for each of the six well-resolved quartets. Unperturbed frequencies for transitions appearing as doublets or poorly resolved quartets were obtained by averaging of component frequencies using weights proportional to calculated intensities. These frequencies were combined with those of the transitions occurring as single, unresolved peaks giving a total of thirty lines. The rotational constants were then determined by a least-squares fit, the standard deviation of which was 0.20 MHz. The rotational constants are given in Table IV. For the first and second excited states of H&CHC035C1 and for H&CHC037C1 the frequencies used were those given directly by the quadrupole analysis and those of completely unresolved transitions. For the third and fourth excited states the procedure is essentially similar to that used for
450
KEWLEY,
34234
233
s-trans
HEMPHILL,
AND
CUILL
231
232
acryloyl
34230
MHz
chloride
6 microns
4.2 kv/cm
FIG. 1. 3VZ1 nuclear quadrupole hyperfine structure of the 511 + 615 transit,ion of s-trank: acryloyl chloride. This is a typical example of the type of resolved hyperfine quartet Itsed in the quadrupole analysis for the ground vibrational state of H&CHC036Cl. TABLH NUCLE.IR
QU.\DRUPOLE
Species H,CCHC03VZ1 H&CHCO=Cl H,CCHC036Cl H,CCHC03’Cl
COUPLING
III
CONRTISTS
x,,(MHz) (g.s.) (T = 1) (T = 2) (g.s.)
O.Ci(O.1) O.l(O.2) 0.8(2.0) 0.3(0.2)
OF S-TRAM
ACRVLOYL
CHLOKIDE
x&MHz)
,&MHz)
-24.4(0.3) -23.6(0.5) -23.7(3.2) -17.2(O.B)
23.X(0.2) 23 .5 (0.3 22.9(1.2) 16.9(0.4)
)
the ground state except that> t’here are no unperturbed frequencies from quad-. rupole analysis to consider. The standard deviations are given at the foot of Tables I and of II. As already mentioned above, rotat’ional transitions of HsCCHC03?3 in four excited vibrational states were observed in addition to the ground state lines., The values of the intertial defect A = I, - I, - Ib for the ground stat,w Oi H&CHC035CI and H&CHC03’C1 confirm the planarity of the s-trans con-. former. ills0 it may be seen that there is an approximately linear decrease in. A for successive excited states. The A values show that the vibration is an out-. of-plane mode. The fact, that these are strong satellites confirms their assignment,
3
* Conversion
;, (1162) Ih ((hi’) I, (udS, A (d2j
A (MHz) B (MHz) G (MHz)
fahor
~.“__
5550.57(0.07) 3807.3e(0.01~ 2265.29(0.01) -0.061248 91.0496 132.7369 223.0963 -0.6902(0.0021)
...___. r=l
= 5OW77 MHz uA2
~-~___
5546.24(0.05) 3821.10(0.0~) 2262.07(0.01) -0.050571 91.1207 132.2596 223.4135 0.0333(0.0017)
_^~__._“__.___ gs. .~
-.-
TABLE
IV
7=3 5563.49(0.09) 3780‘13(0.01) 227O.OO(O.O1) -0.082972 90.8381 133.6930 222.6330 -1,8981(0.0023)
5556.26(0.09) 3793.74~0,01) 2267.88(0.01) -0.071945 90.9563 133.2134 222.8412 -1.3285(0.0023)
H2CCHC03Tf 7=2
-_-.~---
._~ 5570.84(0.20) 3766.53(0.02) 2271.80(0.01) -0.094211 90.7183 134.1758 222.4566 -2.4375(0.~~)
--____.-_-“.-. 7=4
IIUT.SIYON.~LCONST.\NTS AND MOMENTS OF INEBTU* OF ;Y-TR.INS ACRYLOYL CRLOR~DE _~ ___I_~~~~ ~-..
_
5472.43(0.10) 3753 34 (0 ‘ 02) 2226.20(0.01) -0.058802 92.3497 134.6293 227.0133 0.0343 (0.0030 )
HzCCHCWCl -,--_g.s.
to ihe torsional motion about the CX single bond. ~4ppr(.)~irnat~rclativc intrw sity nl~asuremen~~ on the transitions & -+ &r, &:j 3 631, 6, + 716, 7,,~ --) SOB: and 717- sa were made yielding an average value 95 (2.3) cm-’ for the ftyrwnc>; of the torsional vibration, which is a little lowr than the value of 115 (25) cm f~lund in acryloyl fluoride @), as expected from the increased halogen mass. The torsional k~~urnry may also be &imated from the inertial defect, rclatir~~l((;I A@ = 1) -
A(/I
=
Oj = -l(h/S~~~)(l&+
l.Ysing the values of A from Table IV a value of ‘34 cmC’ is obtained, in good agrw mc>nt with the figure from intcrlsity measurements. I:ull use of thcl spwtrcmettsr intcrlsity measuring capability was unfort~unatcly not possible for acryloyl &oridtl bwzause the dpnw sp~k(~tr~lrn produws v~~riati(~I~ of hasrlinc and malty WSP~ t )f overlapping pcalts. J1Il’OLE
M0MJ5NT
Thrt tlcct,ric dipolc momtwt of s-trans acryltryl chloride was determint~d by ~~(~~UreI~l~rltof the St,ark Iobw of the tran&ions given in Table V. In making thtase measurements pressures in t,hc range E-30 ,~m were used giving a t8ypic:tl signal-to-noise ratio of about, 40: 1 for the unshifted line and in t,he rangch 5: 1 to 10: 1 for the Stark lobes. E’requenciw of Stark lobes could be mt~asurcd to ~0.1 ,1IHe or better. The J = i --+ 5 and 5 ---f 6 transitions of Table V ww s&&cd on t,he basis of involving 1~~1s with wry small q~adrupol~ enrrgirs :tntl also having few and very weak nrarby interfrring lines. Electric field valuw uwd were generally in thr rangcl 500-2‘200 V cm-‘. The points used in thtb dctwmination of the St’ark lobe spwds all lay wry ~loscly on linear AV vww~s 1s”
MICROWAVE
SPECTRUM
OF s-TRANS
HzCCHCOCl
453
plots. Since no curvature of the type that might occur for the intermediate field case, due to comparable nuclear quadrupole and Stark interaction energies, was noticed in the plots, the high field case or usual Stark effect equations were used in determining pa and pb. For t’he 101 + 202 transition t’he quadrupole pattern covers a wider region of frequency (6 MHz) than for t’he other lines used in Stark measuremcnt’s. However the M = 1 lobe could be followed in the range 11489 to 11508 MHz and gave a linear Av versus E2 plot. Following least-squares fitting to obtain the values of pL,and pb the calculated Av/E’ values arc found to be self-consistent indicating that the treatment used is satisfactory. The value of 3.12 D for the total dipole moment is similar to that of 3.26 D found in s-tram acryloyl fluoride. The Stark cell was calibrated with methyl acetylene which has a dipole moment of 0.784 (0.001) D when referred to the value of pots = 0.71521 (0.00020) D (7, 8). This method of calibration was used because the Stark lobes of the J = 2 -+ 3 transition (ground vibrational state) of OCS arc not well separated from the line for St’ark fields in the range 0 to about 1500 V cm-‘. DISCUSSION (i)
Molecular Stmctwe
Tho structure of s-t,rans acryloyl chloride is defined by seven bond lengths and six angles, thirteen parameters in all. The analysis of the spectra of HzCCHC03%1 and HzCCHC037C1 (ground vibrational state) yields a total of four independent rotational constants because of the planarity of the molecule. Thus assumptions must be made concerning nine structural parameters in order to obtain information about the remaining four from the observations. There are obviously many ways in which this could be done. The following procedure is considered to be the most satisfactory. H3 H2\
Ct
/ c3 \ / HI
c-C 2
/ I \
0
The structure of the vi@ group is taken to be the same asoin acrolein (1) HZ-C3and3H-C3 = 1.086 A, C&-HI = 1.084 A, C&=Cz = 1.345 A, LHS-C3---C2 = 120.0”, L HZ-C&C, = 121.5” and L C&C&-H1 = 122.8”. Ther eare six parameters remaining. The paramet,ers of the CCOX group for molecules related to s-trans acryloyl chloride ar’c summarized in Table VI. It may be seen t,hat
so. of isotopic species studied
Molecule
H,CCHCOCl HsCCOCl~’
C-C(A)
2 10 1 8 11 9
H?(:CIICOF~(,~-trarts) 11.(‘COF” H~(‘CHCHOr(.s-tr~tts, H:tCCHO’
1, -L7(i 1.499 (1.49) 1.503 1.470 1.501
a S = Cl, F or H. t>l
of the methyl
rcplawmc~nt
distance
in the aldehydes,
fc)re it is reasonable
c-o
c-sc:l,
1.81(i l.iSY
C-C-S(“)
l.l92(nss.) 1.192 (1.18) 1.181 1.219 1.210
(1.35) 1.348 1.108 1.114
least squares
(a)
C-C-0(“,
116.3 112.7 (111.3) 110.3 115.1 117.5
127.2(:tss.) 127.2 (127.0) 128.5 1’,3.3 I . 123 !4
(10).
group by vinyl
has very
little
effecf
on the C’=O
for xvhich the st,ruct~urw are known accurately.
to take
the C=O
distance
in s-trans
acryloyl
There
chloride
as
fixed at the acetyl chloride value, 1.192 8 (9). Both of t’hesc molecules have the same coplanar HICsCIO arrangement. Also there is only a small change in the C--C=0 chloride
angle between it is justifiable
acctaldrhydr
value of 127.2”. The C-Cl arryloyf ehloridc &TtrOn to keep this parameter
112.ci” (acetyl
chloride
=
value).
119,s” With
were A = 5374.20
and K = 0.217593.
A partial
in s-trans
into
to change
MHz,
acryloyl c&hloride slightl)
the s-trans
(4 ) it was dwided value of 1.7S9A as
and their initial values were Cm X‘? =
(acrolrin
t,his assumed
structural
only
consideration
value of 1.74 (0.02)8 assigning it an initial
The othw three variables
L C,=C--Cl
tional constants
but in order to take
diffraction as a variable,
1.4-70 A and
so that
angle as fixed at t’he a&y1
bond length would he expected
bet n-wn the t\vo chlorides
in acetxl chloride.
and acrolcin
to take the C-C=0
values)
R = 4193.24
refinement
and
structure
L C,--Cr
X11 =
the calculat cd rota
JfHz,
(! = 2355.42
was achieved
;\IHz
by varying
thus
four paranwtcrsC&Cl, C,---Cl, L Cr=C2----Cl and L C-C--Cl to fit t,he otwrwd B and C rOtatiOna constants of the ““Cl and “‘Cl species of s-trans ncryloyl chloride. These
rotational
constants
were selected
because
they are more accurat PI,I
determint~d than the A rotational constants. The results of the fitting procedurc~ arc summarized in Table VII. Error estimates were obtained by allowing all sev(~n heavy atom parameters t(J vary and using the diagnostic least-squarw nicttrotl (10). This method wxs not used for the refinement8 of the structural p:uwnc~t,c~rs:ts it \\-a~found that the initial struct~urc was not
rlow
mough
to
th
tinal
OIW
for t,lrcL
MICROWAVE
~PFXTRUM TABLR
H,CCHCOCl
4;55
VII
P.\n LMETERS :\ND PARTIAL REFINEMENT nv FITTING TO B .\NU C ROTATIONAL CONSTANTS
ASSUMED
STRUCTUR.~L
Parameter*
Heavy
OF s-TRANS
Assumed
Estimated SE
Refined
SE
atom 1.470 1.789 119.8 112.6 1.345 1.192 127.2
Ii (CC) IL(C-Cl) L c=c-c L C-C-Cl R (C=C, R (C=O) L c-c=0
0.01 0.02 1.8 3.0 0.01 0.02 3.0
1.476 1.816 122.6 116.3
0.01 0.02 1.5 1.0
Hydrogen” PR(C-H) R(C-H) L C=CH L C=C-H L C-C-H
1.086 1.084 121.5 120.0 117.4
(outer) (inner)
0
8 All distances are in A, all angles in degrees. s Uncertainties in the hydrogen parameters were not included when estimating the errors in the refined parameters since the calculated rotational constants are relatively insensitive to the hydrogen positions.
assumption that the rotational constants vary linearly with changes in the parameters to be valid. The most significant result of the fitting is the 3.7” increase in the C-C-Cl anglr and thr decrease in the estimated standard error in this angle from 3.0 t,o 1.O”. The refined angle is quite close to the C-C-H (aldehydic) angle of 115.2” (0.2”) 111acrolcin (I), which could have been an alternate initial estimate. It should be noted that the C-C-C angle also increases, by 2.8”, relative to the acrolein value. The opening up of both of these angles between the assumed and refined structures suggests that some increased repulsion between the vinyl group and the X atom of the CCOX group is introduced when the aldehydic hydrogen is replaced by chlorine. The results also indicate that the C-Cl bond length may bc slightly greater in s-trans acryloyl chloride than in acetyl chloride. Although this last conclusion is questionable it can be stated with confidence that the prosent work shows that the electron diffraction value for the C-Cl bond length of 1.74 (0.02)A is too low. The T’~substitution coordinates of the chlorine atom were calculated from the changes in the moments of inertia 1, and Ib on isotopic substitution. The coordinates arc 1 acl 1 = 1.085 (O.OOl)A and 1bcl 1 = 0.816 (0.005)B. The angle of rotation of the principal axes on isotopic substitut’ion is determined to be 2.3”.
KEWLEY,
4.56
HISMPHILL,
ANI)
CURL
(ii) Nuclear Quadrupole Coupling Constants The calculation of the quadrupolc principal axis elements xTZand xzlz,rcyuires a knowledge of the off diagonal element xd in addition to the c>xperimclntal xnu and xbbvalues. Unfortunately, in the present case the angle of rotation of principal inert,ial axes on isotopic subst,itution is too small and t,hr (‘rrors in thta “7c’1 species quadrupole coupling constants arc too large to allow a mc,aningful rstimate of Xab to be made. 111 interpreting the nuclear quadrupolc coupling constants of awtyl ChkJridc' Sirmot t (9) considered the rcsonancc st#ructurw
CRO@c/o-
H3C -
H$
I
\
CL
-
ci,
II
\
Ct+
Of
H,Cm
Ct
and deduced that the C-Cl bond has 9 ‘? double bond character and 41’ ‘G ionic character. It is of interest t#oconsider if replacement of the methyl group 1)~ thus vinyl group of s-trans acryloyl chloride favors the type II resonanw structuw because of conjugation of the H&=CH and C=Cl+ bonds. The affect \\ould cause loss of electron density from the chlorine, 3p, orbital and rcduw the: valw of_xZibelow the acetyl chloride value of xZZ= “1.6 (1) I\lHz. Thr c~xptrrimcntal value of 23.8 (0.2) l\$Hz for s-trans acryloyl chloride (see Table III) dors not indicate increased C-Cl double bond charactw but rather that the C:LCl bond is very similar in the two molecules. (iii)
Other Con_fomers
The observed dipole moment components of the s-trans form of 2.76 and 1.45 D when resolved in relation t’o thtl C-C single bond direction yield ~11 = 3.00 and pLI = 0.84 D. If as in acryloyl fluoride a vinyl group p,. rnornt>nt,(If about, 0.S D is present, directed towards t’he rest of the molecule, thaw it is most, reasonable to choose t’he direction of ~1as bet~wwn t’he C-Cl and C-O bonds and making an angle of 34.3” with the C-O direction, see Fig. 2. An approximate barediction of t’he dipole components and also th(, rotational constants of th(s s-cis form may be made by assuming the structure to be derived from the s-trans form solely by a 180” rotat’ion of the COCl group about the C-C single bond. The cxstimated quantities are pC(a = 2.7 L>, ,.L!,= 1.5 I), pCctot = 3.1 D, orientrd at’ 62’ to t,hcx carbon-oxygen bond and between the C=O and C--Cl directions, ,4 = 95X,5 AlHz, B = 2524 MHz, C = 1998 MHz and K = -0.861. The direction of the predicted dipole moment and principal a and b axes arc shown in Fig. 2. On this basis the “Ro,l type lines of the s-cis form falling in the 26.5-40 (;Hz range arc’ those of the J = .5 + 6, 6 --s 7 and 7 j s transitions. A consid~~rablr~
MICROWAVE
SPECTRUM OF s-TRANS H&CHCOCI
4.77
b
H
i.,.._._ __... ‘/ cc ;
Cl
c
pot
Cl
C-
H
\
/
0
‘a S-CIS
S -TRANS
(Predicted) FIG. 2. Dirertions of principal u and b inertia axes and electric dipole moment for s-trans acryloyl chloride together with the predicted directions for the a-& conformer. The total dipole moment is oriented at 27.7” to the principal Q-axis and at 33.3” to the C=O bond direction in the s-trans form. For t,hes-cis form the total dipole moment is predicted to make art angle of 33.7’ with t,he principal a axis and 62.3” with t,he C=O direction. amount of time has been used in trying to identify these peaks amongst the many strong lines of the s-trans form. An assignment has not yet been made even though a number of lines have bcrn studied in the 33-34 GHz range which show nuclear quadrupole hyperfine st,ructurc and are very likely not due to t,he s-trans form. In the infrared study (5) it was mentioned that there was no definite evidence that could rule out a skewed or gauche form as the less abundant conformer. Also in electron diffract,ion work on oxalyl chloride (15) the results at 0°C show that the gas is a, mixt,urc of s-trans and gauche conformers with t,he latter in 83 5%abundance. It may be that acryloyl chloride has a gauche conformer although this is not considrred very likely in view of the s-trans and s-cis conformers being found for acryloyl fluoride (.2). RECEIVED:
April
12, 1972 > REFER P’NCES
1. E. A. CHERNIAK AND C. C. C~STAIN, J. Cihcrn. Phys. 46,104 (1966). 8. J. J. KEIRNS AND R. F. CUBL, Jlt., J. ChmL. Phys. 48, 3773 (1968). 3. G. L. CARLSON, W. G. FATELEY, AND IL E. WITKOU’SKI, J. Aweer. Chevn. Sot. 89, 6437 (1967). /t. T. U~JI, Bull. Chew Sot. dap. (~~?ip~vn~u~a~~~ui) 30, 737 (1957). 5. J. E. KATON AND W. R. FEAIRHELLER, J. Chm. Phys. 47, 1248 (1967). 6. J. H. H@c, L. NYGAAED AND G. 0. SORENSEN, J. Mol. Stmct. 7, 111 (1970). 7. J. S. MUENTER AND V. W. LAUHE, J. Chcm. Ph,ys. 46,855 (1966). 8. J S. MUENTER, J. Chcm. Phys. 48, 4544 (1968). 9. K. M. SINNOTT,J. Chcm. Phys. 34, 851 (1961).
158
BEWLEY,
HEMPHILL,
ANI)
CURL
10. R. F. CURL, JR., J. Computational Phys. 6, 367 (1970). 11. L. PIERCE AND L. C. KRISHEH, J. Chem. Phys. 31, 875 (1959). 12. IL. W. &LB, C. C. LIN AND E. B. WILSON, JR., J. Chem. Phys. 26, 1695 (1957). 13. Ii. HEDBERG, Fourth Austin Symposium on (+as Phase Molecular Structure, The Un versity of Texas at Austin, 1972. Paper W2.
OF MOLECULAR
Microwave R.
SPECTROSCOPY
Spectrum
of Chemistry,
(1972)
of s-Trans
D. C. HEXPHILL~
KEWLEY~,
Department
44, 443-458
AND
Rice University,
Acryloyl 3%.
Chloride’
F. CURL, JR.
Houston,
Texas 77001
The microwave spectrum of acryloyl chloride, H&CHCOCl, has been irivestigated in the S-40 GHz region. The spectra of the species H,CCHC03”Cl and HsCCHCOWI of the s-trans conformer have been assigned. The rotational constants and nuclear quadrupole coupling constants for the ground vibrational state are (in MHz): H&CHCOWl: A = 5546.24, B = 3821.10, C = 2262.07, xoo = 0.6, ebb = -24.4 and xcc = 23.8; H&CHCOWl: A = 5472.43, B = 3753.84, C = 2226.20, xaa = 0.3, XW, = -17.2 and xce = 16.9. The dipole moment components for H&CHCOWI are (in D) : p, = 2.76, ~6 = 1.45 and gtut = 3.12. The spectra of the first four excited vibrational states for torsional motion about the C-C bond have been assigned for the Wl isotopic species. From relative intensity measurements the torsional frequency is determined as 95 tlr: 25 cm-‘. Some lines which may be due to a secaond conformer (cis or possibly gauche) have been observed but not. yet assigned.
Acryloyl chloride, H&HCCOCl, is an example of an interesting type of molecule which may have two conformers related to each ot’her by rotation about a C-C single bond which is situated between conjugated double bonds. A number of molecules stru~turall~rsimilar t.o acryloyl chloride have been skdied by microwave spect,roscopists. Of these the most closely related are acroIein, for which only the s-trans form could be detected in a very careful investigation (1) and acryloyl fluoride (2). Both s-cis and s-trans forms of acryloyl fluoride were observed. From relat,ive intensity measurements the s-trans isomer was shown to be t,he more stable by 90 f 100 cal/mole, in good agreement with the value for AH of 150 f 100 caI/mole which was determined by studying the temperature variation of int,ensities of absorption bands in the infrared spectrum (3). In his electron diffraction study of acryloyl chloride, Ukaji (4) interpreted his results in terms of a predominant s-trans isomer together with a smaller propor1Acknowledgment is made to the donors of The Petroleum Research Fund, administered by the American Chemical Society, for support of this research. This work was also supported by grants from the National Science Foundation. 2 Present address: Department of Chemistry, Queen’s University, Kingston, Ontario, Canada. 3 Present address: Environmental Protect,ion Agency, Durham, N.C. 443 Copyright All rights
0
1972 by Aademic
of reproduction
in any
Press, form
Inc. reservzd.
44-l
KEWLEY,
HP:MPHILL,
.4X1) CURL
tion of a second conformer, assumed to bc the s-cis form. The structural paramc ters obtained were quite similar to the corresponding ones in acrolcin. The clearest evidence for the existence of two conformers is the infrared work of Iiaton and Feairheller (5) in which the trmpcraturc variation of rclativc intcn sities of the C-Cl stretching bands of t,he s-cis and s-trans conformers was invcst’igated and the s-trans form found to be the more stable by 0.6 kcal/molc. This figure indicates that at 25°C the concentration of t’hr s-cis form should hr al)out, one third of the s-trans form so that the microwave spectra of both conformers should be observable. Although there are indications in the present work t’hat the s-cis form is pres-, ent, the spectrum of that conformer has not yet been assigned. This report deals almost entirely with the rotational spectrum of s-trans acryloyl chloride. EXPERIMENTAL
Samples of acrylopl chloride were purchased from Aldrich Chemical Company Inc., Milwaukee, Wis. Although the substance is known to be moisture sensitive it was found satisfact’ory to use the samples without further purification. The samples were stored in t,he dark at -20°C. Acryloyl chloride changes from colorless to straw-colored after prolonged exposure to light at room temperatjurr. The initial work in the 7.5-26.5 GHz region was done with a conventional 100 kHz Stark modulation spectrometer with oscilloscope display, mostly at dry ice temperature. The 26.5-40.0 GHz region was observed with a Hewlett Packard 84608 spectrometer, mainly at room temperature. Samplr pressures in the range 5-30 Mmwere employed. The accuracy of measurrmcnt for the Hcwlctt Packard spectrometer is in t,he range ho.01 to +0.05 MHz wherea,s for t,hc 100 kHz Stark modulation instrument the accuracy is about f0.3 :\lHz. ROTATIONAL
SPECTRUM
Approximate calculations from assumed structures predicted that the s-trans form should be highly asymmetric with K in the range 0.3 to -0.2 and that, the s-cis form should be a slightly asymmetric top with K in the range -0.8 to -0.9. Both conformers should have observable u-type and b-type t#ransitions. The observed 7.5-26.5 GHz spectrum nas found to be a, very rich one, complicated by the nuclear quadrupole splitting due t,o the chlorine atom. An initial assignment of the transition 2pl + 313 was made from the Stark effect. ,4 number of other low J lines were similarly assigned allowing approximat)e rotational constants of s-trans H,CCHC035Cl to be determined. However, attempts to assign the individual nuclear quadrupolc hyperfine components of these low ./ transitions proved unsuccessful on account of the extra and unrelated lines usuall> found near or within a hypcrfine pat’tern. The approximate rotational constants were confirmed by prediction and sub-
MICROWAVE
SPECTRUM
OF s-TRANS
HzCCHCOCl
445
sequent observation of higher J transitions in the 26.540.0 GHz range. The transitions found were mostly of the type ‘Ro, 1 although a few bR1,l and bR_l,l lines were also recorded. The intensities in the group of lines 616---f 7,,, , t& + TIT, 606+ 707and 606-+ 717which falls between 33930 and 33940 MHz (see Table I) allowed the ratio ~02/~2 to be estimated at about 3, which later helped in the assignment of Stark lobes. The characteristic pattern of this group also greatly facilitated the assignment of the corresponding set of lines for t,he HzCCHC037C1 species (see Table II). In addition, four set’s of vibrational satellites of H&CHC035C1 were assigned. (ii) Analysis
of ,Vuclear Quadrupole HyperJine Structure
Because of the difficulty of assigning quadrupole components for the low J lines and because of the much better accuracy of measurement in the 26.5-40.0 GHz region, it was decided to rely on the measurements in the higher frequency range to determine quadrupole coupling constants. For the H&CHC035C1 species in the ground vibrational state well resolved quartets were found for the six transitions 413+ 514, -I40-+ h , 514+ 615, 523 -+ 624, lidI--+ 6~ and 5~ + 6j1 . The 514-+ 616transition is shown in Fig. 1. For these six transitions it was found that the pressure had to be less than 10 pm to achieve satisfactory resolution of the members of each of the two closely spaced doublets. This naturally resulted in a rather poor signal-to-noise ratio (about 15: 1 for 514+ tj15). However, the frequencies of the four components could still be measured with a reproducibility of bett’er than ho.05 MHz. A least-squares fit was performed for the twenty-four quadrupole components to give the six unpert,urbed line frequencies and the values of the coupling constants xaa and xcc. The coefficients dv/c?x,a an d dv/dxcc for the least-squares fit were calculated from the equation W, =
Y(F)/J(J
+ 1) [{J(J + 1) + E(K) - (K + 3wm.~Xaa f (J(J + 1) - E’b) + (K - 3&wwd
(1)
The standard deviation of the fit was 0.03 MHz. The st’andard error for each of the six line frequencies from this treatment was given as 0.02 MHz. The resulting coupling constants are in Table III, Xbbbeing determined by the rela0. The uncertainties quoted are the standard deviations tion %% + Xbb + estimated from the statistical analysis of the least-squares procedure. The transitions in which the hyperfine splitting depends most strongly on xaa have the larger values of K1 and so are the weakest for a given J --, J + 1. It was not possible to obtain satisfactory resolution of such transitions for other than the ground vibrational state of HzCCHC035C1. For the weaker absorption peaks of the first and second excited torsional states of HCCHC035C1 and for the ground vibrat,ional state of H&CHC037C1 a slightly different method of xc0
=
KEWLEY,
446
HEMPHILL, TABLE
AXD
CURL
I
OBSERVED FREQUENCIES OF R-TRANS ACRYLOVL CHLORIDE, H?CCHC0”5CI, IN GROUKU AND EXCITED TORSION \I, STATES
10, --f 2%
‘L,?4 313
2z1 + 32.’ 211 + 322
321 --j 422
41s --f 514”
423 ---f 521
422 ---f 5%
432 + 5% la, + 5,,
4 41 ---f 542
3/2 5/2 l/2 312 l/2 512 T/2
---f + + + ---f + --f
gs. 5/2 7/2 l/2 5/2 3/2 712 9/2
5/2 --f 712 3/2 ---f 5/2 7/2 ---f 9/2 l/2 9/2 3/2 7/2
7=1
23 425.60
+ + ---) ---) + + +
7/2 11/2 9/2 13/2 7/2 11/2 9/2
w2 5/2 9/2 712
+ + + ---f
1312 712 11/2 912
34 042.29
lu2 5/2 4
7/2 1312
34 043.08
5/2 11/2 7/2 9/2 5/2 1112
7/2 13/2 912 II/2 7/2 13/2
23 431.47 27 579.4ti
31 904.16
31 817.13
9/2 11/a
31 905.36
31 818.24
7/2 13/2 9/2 11/2
32 32 32 32
27 3’2t2.48”
27 579.86 27 29 29 29 29
580.37 980.00 980.66 982.66 983.51
28 926.82 28 927,87 ’
31 380.79”
+ + --) --)
7=4
15 548.58 18 250.00* 23 121.23
5/2 9/2 7/2 11/2 512 912 7/2
5/2 11/2 7.0 9/2
7=3
15 547.56
3/2 11/2 5/2 9/2
+ + ---) ---f + +
7=2
11 482.83 11 185.47 11 GB.18 15 546.57
4 + +
712 + 9/2 + 440 + 541”
vo~,aci(MHz)
F F’
Transition
280.09 280.53 282.04 282.52
28 908.86
28 887.33
28 862.87
28 8:Qi.41
28 909.88
28 888.39
28 864.03
28I837.54
33 894.41&
33 816.84%
31 250.98”
31 182.71a
31 317.03” 33 90G.94
33 637 .03
33 908.73
33 638.72 31 637.69a
31 112.788
MICROWAVE
SPECTRUM TABLE
Transition
515 4
5 15 -+
50~ +
50 +
514 -+
513 4
9/2 11/2 7/2 13/2 616 9/2 11/2 7/2 13/2 60s 9/2 11/2 7/2 13/2 610 9/2 11/2 7/2 13/2 61j” 11/2 9/2 13/2 7/2 624b 11/2 9/2 13/2 7/2
524 + h5
5 33 --t h4
541 -+ 64~~
5rz ---f 643
5ao + 6~~
H,CCHCOCl
I-Contin~d
7=1
g.s.
--f 11/2 + 13/2 + 9/2 + 15/2 4 11/2 + 13/2 ---t 9/2 + 15/2 4 11/2 + 13/2 ---t 9/2 + 15/2 + 1112 + 13/2 + 9!2 -+ 15/2 --f 13/2 + 11/2 + 15/2 + 9/2 ---f 13/2 + 1112 --i 15/2 + 9/2
29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 29 34 34 34 34 39 39 39 39
397.63 397.82 398.14 398.32 403.19 403.36 403.66 403.98 420.36 420.58 420.88 421.11 426.07 426.19 426.47 426.66 231.00 231.36 232.85 233.23 478.87 479.58 480.89 481.58
1112 + 9/2 +
1312 11/2
33 767,87
‘;;;
$
29 29 29 29
7=2
7=3
29 448.07*
29 4l39.19a
34 34 34 34 39 39 39 39
34 34 34 34 39 39 39 39
244.48 244.83 246.42 246.74 442.91 443.60 444.85 445.50
29 485.50a
33 739.18
33 768.98
33 763.62
33 753.65
33 740.26
11/2 9/2 ---f + 1112 1312
37 og4, l4
37 038.31
36 979.22
13’2 7/2 ---f ----)912 15’2
37 094.58
37 038.79
36 979.60
7/2 13/2 9/2 1112 7/2 13/2
9/2 15/2 11/2 13/2 9/2 15/2
39 39 39 39
38 408.93
39 309.47
11/2 g’2 +
1l’2 13/2
38 409.45
39 309.98
7/2 13/2 9/2 11/2
9/2 15/2 11/2 13/2
38 38 38 38
+ + --t +
771.52 771.79 773.48 773.80
430.26 430.50 431.72 431.94
29 498.42a
254.44 254.72 256.37 256.79 403.78 404.26 405.49 406.07
33 752.56
+ + --t + + +
7=4
429.48 429.64 429.97 430.16
33 762.57
7
447
yot,sd (MHz)
F F’
606
OF s-TRANS
36 917.50”
36 852.84a
39 292.84
39 133.30
39 294.76
39 135.22
38 103.948
448
KEWLEY,
HEMPHILL,
.4NU CURL
TABLE I-Continued Transition
G16--) 701 (i*F,4 7,i (i”6 + 707 6°C 4 711 cil:, ---tii, 13/2 --t 11/2 + 15/2 1312
GI:,-
7~
701 - 80s 7Ii ---f 818 SD UC
~oi,-d(MHz)
F F’
7=
5s
33 33 . 33 33
93l.lV 912.4V t 936.7V 938.0-P
1
33 96-l. 17a 33 965.55* 33 97o.ooa
7=4
34 010.54~ 34 026.31~ 34 015.96* 34 032.08”
38 598. O’LL 38 528, 84a 38 496. 90a 38 527.60” 0.14 0 l(i
38.553.138 38 572.w 38 551.78* 38 570.69” 0.14 0.20
38 595.74
15/2 ---) 1712 912 + 11/2 38 581.60
38 596.96
13/2 + 1112 + 15/2 1312 38 11g.78
38 425.71
15/2 9/2 + 4 1712 11/2 38 -J20.76
38 426.70
_
7=3
33 991.01a 33 995.90a 33 997.53’
38 580,14
38 158. 31ja 38 157.333 0.20
T=2
* No qultdrupole structure was resolved. b Transition used in 35C1quadrupole analysis, gro\uld state. c For least-squares fit, to rotational constants. analysis was used.
In these cases all observed yuadrupole component’s, including poorly resolved quartets and mcmbcrs of doublets, w-erc used in least-squares fitting. When two strong quadrupolc: components are observed as a single peak the coefficients of xaa and xcc for each component were calculated. An average coefficient
for each of xaa and xcc was then calculated,
of the two components
in proportion
to their calculated
weighting
the coefficients
intensities.
It may be seen from Table III that thr values of xaa, Xbband xECfor the first and second excited torsional states agree wit’h the values for the ground &ate within experimental error. The ground state coupling constants are more accurate, however. The element xcc corresponds t’o a principal value xrr of the quad-rupole tensor. The observed xcc for H2CCHC05’Cl should thcrcforc bc lower than xcc for H$2CHC035C1 by a factor QzT/Qsj= l/1.26%. A value of 23.S/1.26%S = IS.8 f 0.2 MHz is expectctd for xec compared t)o the experimcnt’al value of 16.9 + 0.4 MHz. One part’ial explanation of the discrepancy may be that’ as overlapping of adjacent lines becomes mow pronounced the observed hyperfine splittings are less than would be found if line widths wtre negligible so that, coupling con stants will tend to appear lower than the true values. Direct comparisons cannot be made for xoa and Xbbof the “‘Cl and 37C1 species because of tht: rotation 06 principal axes on isotopic substitution. Quadrupole analysis was not attempted for the higher excited states because of insufficiency of data.
MICROWAVE
Sl?ECTRUM TABLE
OBSERVED
FREQUENCIES
Transition 413 ---t 514
413 +
5%
432 --f 5a3 4 (0 + 541
F E’ Q/2 7/z 11/2 5/2 Q/2 7/2 11/Z 5/a 5/z II/2 7/2 Q/2
51: + 6”s 51: --t 61s 505 ---f 606 505 --f 616 514 + 615
1312 7/2 11/Z 5% + 6% Q/2 L3/2 712 St. dev. (r = 0.25 8 No quadrupole
--) --) + --) + -+ + -+ + -+ +
-+ ---t --t t + --t
7/‘2 13/z Q/2 11/a
1512 Q/Z 13,‘2 llj2 15/Z 9/z
HzCCHCOCl
449
II
OF S-TRANS ACRYLOYL CHLORIDE, H~CCHCO~CI, GROUND VIBR.%TION~L STATE Vobsd(MHZ)
11/2 Q/2 1312 7/2 U/2 Q/2 13/Z ?/2
OF s-TRANS
29 29 29 29
513.62 514.27 515.45 516.09
28 455.58 28 456.33 30 31 31 31 31 28 28 28 28 33 33 38 38 38 38
845.538 701.11 701.56 702.58 702.80 931.22” 936.86~ 954.76% 961.13% 699.21 699.56 846.12 846.62 847.56 848.05
Transition
F P’ 11/2 9/2 13,/Z ?/2 11/2 Q/2 13/2 7/z
-+ -+ -+ ---t --f -+ --, +
m.d(MHZ) 13/2 11/2 15/2 Q/2 1312 11/2 15/2 9/z
33 225.82 33 226.65 36 474.14 36 474.61 33 392.84” 33 394.40% 33 398.86*
13/2 U/2 15/2 Q/2 13/Z U/2 15/Z Q/2
3 -+ ---f + -+ -+ -3 --+
15/2 13/2 I?/2 11/Z 15/2 13/2 1712 11/z
37 973.94 37 974.69 37 807.99 37 808.71 37 848.56” 37 847.3P
st,ructure was resolved.
The quadrupole analysis for the ground vibrational state of H&CHC035C1 yielded the unperturbed frequencies for each of the six well-resolved quartets. Unperturbed frequencies for transitions appearing as doublets or poorly resolved quartets were obtained by averaging of component frequencies using weights proportional to calculated intensities. These frequencies were combined with those of the transitions occurring as single, unresolved peaks giving a total of thirty lines. The rotational constants were then determined by a least-squares fit, the standard deviation of which was 0.20 MHz. The rotational constants are given in Table IV. For the first and second excited states of H&CHC035C1 and for H&CHC037C1 the frequencies used were those given directly by the quadrupole analysis and those of completely unresolved transitions. For the third and fourth excited states the procedure is essentially similar to that used for
450
KEWLEY,
34234
233
s-trans
HEMPHILL,
AND
CUILL
231
232
acryloyl
34230
MHz
chloride
6 microns
4.2 kv/cm
FIG. 1. 3VZ1 nuclear quadrupole hyperfine structure of the 511 + 615 transit,ion of s-trank: acryloyl chloride. This is a typical example of the type of resolved hyperfine quartet Itsed in the quadrupole analysis for the ground vibrational state of H&CHC036Cl. TABLH NUCLE.IR
QU.\DRUPOLE
Species H,CCHC03VZ1 H&CHCO=Cl H,CCHC036Cl H,CCHC03’Cl
COUPLING
III
CONRTISTS
x,,(MHz) (g.s.) (T = 1) (T = 2) (g.s.)
O.Ci(O.1) O.l(O.2) 0.8(2.0) 0.3(0.2)
OF S-TRAM
ACRVLOYL
CHLOKIDE
x&MHz)
,&MHz)
-24.4(0.3) -23.6(0.5) -23.7(3.2) -17.2(O.B)
23.X(0.2) 23 .5 (0.3 22.9(1.2) 16.9(0.4)
)
the ground state except that> t’here are no unperturbed frequencies from quad-. rupole analysis to consider. The standard deviations are given at the foot of Tables I and of II. As already mentioned above, rotat’ional transitions of HsCCHC03?3 in four excited vibrational states were observed in addition to the ground state lines., The values of the intertial defect A = I, - I, - Ib for the ground stat,w Oi H&CHC035CI and H&CHC03’C1 confirm the planarity of the s-trans con-. former. ills0 it may be seen that there is an approximately linear decrease in. A for successive excited states. The A values show that the vibration is an out-. of-plane mode. The fact, that these are strong satellites confirms their assignment,
3
* Conversion
;, (1162) Ih ((hi’) I, (udS, A (d2j
A (MHz) B (MHz) G (MHz)
fahor
~.“__
5550.57(0.07) 3807.3e(0.01~ 2265.29(0.01) -0.061248 91.0496 132.7369 223.0963 -0.6902(0.0021)
...___. r=l
= 5OW77 MHz uA2
~-~___
5546.24(0.05) 3821.10(0.0~) 2262.07(0.01) -0.050571 91.1207 132.2596 223.4135 0.0333(0.0017)
_^~__._“__.___ gs. .~
-.-
TABLE
IV
7=3 5563.49(0.09) 3780‘13(0.01) 227O.OO(O.O1) -0.082972 90.8381 133.6930 222.6330 -1,8981(0.0023)
5556.26(0.09) 3793.74~0,01) 2267.88(0.01) -0.071945 90.9563 133.2134 222.8412 -1.3285(0.0023)
H2CCHC03Tf 7=2
-_-.~---
._~ 5570.84(0.20) 3766.53(0.02) 2271.80(0.01) -0.094211 90.7183 134.1758 222.4566 -2.4375(0.~~)
--____.-_-“.-. 7=4
IIUT.SIYON.~LCONST.\NTS AND MOMENTS OF INEBTU* OF ;Y-TR.INS ACRYLOYL CRLOR~DE _~ ___I_~~~~ ~-..
_
5472.43(0.10) 3753 34 (0 ‘ 02) 2226.20(0.01) -0.058802 92.3497 134.6293 227.0133 0.0343 (0.0030 )
HzCCHCWCl -,--_g.s.
to ihe torsional motion about the CX single bond. ~4ppr(.)~irnat~rclativc intrw sity nl~asuremen~~ on the transitions & -+ &r, &:j 3 631, 6, + 716, 7,,~ --) SOB: and 717- sa were made yielding an average value 95 (2.3) cm-’ for the ftyrwnc>; of the torsional vibration, which is a little lowr than the value of 115 (25) cm f~lund in acryloyl fluoride @), as expected from the increased halogen mass. The torsional k~~urnry may also be &imated from the inertial defect, rclatir~~l((;I A@ = 1) -
A(/I
=
Oj = -l(h/S~~~)(l&+
l.Ysing the values of A from Table IV a value of ‘34 cmC’ is obtained, in good agrw mc>nt with the figure from intcrlsity measurements. I:ull use of thcl spwtrcmettsr intcrlsity measuring capability was unfort~unatcly not possible for acryloyl &oridtl bwzause the dpnw sp~k(~tr~lrn produws v~~riati(~I~ of hasrlinc and malty WSP~ t )f overlapping pcalts. J1Il’OLE
M0MJ5NT
Thrt tlcct,ric dipolc momtwt of s-trans acryltryl chloride was determint~d by ~~(~~UreI~l~rltof the St,ark Iobw of the tran&ions given in Table V. In making thtase measurements pressures in t,hc range E-30 ,~m were used giving a t8ypic:tl signal-to-noise ratio of about, 40: 1 for the unshifted line and in t,he rangch 5: 1 to 10: 1 for the Stark lobes. E’requenciw of Stark lobes could be mt~asurcd to ~0.1 ,1IHe or better. The J = i --+ 5 and 5 ---f 6 transitions of Table V ww s&&cd on t,he basis of involving 1~~1s with wry small q~adrupol~ enrrgirs :tntl also having few and very weak nrarby interfrring lines. Electric field valuw uwd were generally in thr rangcl 500-2‘200 V cm-‘. The points used in thtb dctwmination of the St’ark lobe spwds all lay wry ~loscly on linear AV vww~s 1s”
MICROWAVE
SPECTRUM
OF s-TRANS
HzCCHCOCl
453
plots. Since no curvature of the type that might occur for the intermediate field case, due to comparable nuclear quadrupole and Stark interaction energies, was noticed in the plots, the high field case or usual Stark effect equations were used in determining pa and pb. For t’he 101 + 202 transition t’he quadrupole pattern covers a wider region of frequency (6 MHz) than for t’he other lines used in Stark measuremcnt’s. However the M = 1 lobe could be followed in the range 11489 to 11508 MHz and gave a linear Av versus E2 plot. Following least-squares fitting to obtain the values of pL,and pb the calculated Av/E’ values arc found to be self-consistent indicating that the treatment used is satisfactory. The value of 3.12 D for the total dipole moment is similar to that of 3.26 D found in s-tram acryloyl fluoride. The Stark cell was calibrated with methyl acetylene which has a dipole moment of 0.784 (0.001) D when referred to the value of pots = 0.71521 (0.00020) D (7, 8). This method of calibration was used because the Stark lobes of the J = 2 -+ 3 transition (ground vibrational state) of OCS arc not well separated from the line for St’ark fields in the range 0 to about 1500 V cm-‘. DISCUSSION (i)
Molecular Stmctwe
Tho structure of s-t,rans acryloyl chloride is defined by seven bond lengths and six angles, thirteen parameters in all. The analysis of the spectra of HzCCHC03%1 and HzCCHC037C1 (ground vibrational state) yields a total of four independent rotational constants because of the planarity of the molecule. Thus assumptions must be made concerning nine structural parameters in order to obtain information about the remaining four from the observations. There are obviously many ways in which this could be done. The following procedure is considered to be the most satisfactory. H3 H2\
Ct
/ c3 \ / HI
c-C 2
/ I \
0
The structure of the vi@ group is taken to be the same asoin acrolein (1) HZ-C3and3H-C3 = 1.086 A, C&-HI = 1.084 A, C&=Cz = 1.345 A, LHS-C3---C2 = 120.0”, L HZ-C&C, = 121.5” and L C&C&-H1 = 122.8”. Ther eare six parameters remaining. The paramet,ers of the CCOX group for molecules related to s-trans acryloyl chloride ar’c summarized in Table VI. It may be seen t,hat
so. of isotopic species studied
Molecule
H,CCHCOCl HsCCOCl~’
C-C(A)
2 10 1 8 11 9
H?(:CIICOF~(,~-trarts) 11.(‘COF” H~(‘CHCHOr(.s-tr~tts, H:tCCHO’
1, -L7(i 1.499 (1.49) 1.503 1.470 1.501
a S = Cl, F or H. t>l
of the methyl
rcplawmc~nt
distance
in the aldehydes,
fc)re it is reasonable
c-o
c-sc:l,
1.81(i l.iSY
C-C-S(“)
l.l92(nss.) 1.192 (1.18) 1.181 1.219 1.210
(1.35) 1.348 1.108 1.114
least squares
(a)
C-C-0(“,
116.3 112.7 (111.3) 110.3 115.1 117.5
127.2(:tss.) 127.2 (127.0) 128.5 1’,3.3 I . 123 !4
(10).
group by vinyl
has very
little
effecf
on the C’=O
for xvhich the st,ruct~urw are known accurately.
to take
the C=O
distance
in s-trans
acryloyl
There
chloride
as
fixed at the acetyl chloride value, 1.192 8 (9). Both of t’hesc molecules have the same coplanar HICsCIO arrangement. Also there is only a small change in the C--C=0 chloride
angle between it is justifiable
acctaldrhydr
value of 127.2”. The C-Cl arryloyf ehloridc &TtrOn to keep this parameter
112.ci” (acetyl
chloride
=
value).
119,s” With
were A = 5374.20
and K = 0.217593.
A partial
in s-trans
into
to change
MHz,
acryloyl c&hloride slightl)
the s-trans
(4 ) it was dwided value of 1.7S9A as
and their initial values were Cm X‘? =
(acrolrin
t,his assumed
structural
only
consideration
value of 1.74 (0.02)8 assigning it an initial
The othw three variables
L C,=C--Cl
tional constants
but in order to take
diffraction as a variable,
1.4-70 A and
so that
angle as fixed at t’he a&y1
bond length would he expected
bet n-wn the t\vo chlorides
in acetxl chloride.
and acrolcin
to take the C-C=0
values)
R = 4193.24
refinement
and
structure
L C,--Cr
X11 =
the calculat cd rota
JfHz,
(! = 2355.42
was achieved
;\IHz
by varying
thus
four paranwtcrsC&Cl, C,---Cl, L Cr=C2----Cl and L C-C--Cl to fit t,he otwrwd B and C rOtatiOna constants of the ““Cl and “‘Cl species of s-trans ncryloyl chloride. These
rotational
constants
were selected
because
they are more accurat PI,I
determint~d than the A rotational constants. The results of the fitting procedurc~ arc summarized in Table VII. Error estimates were obtained by allowing all sev(~n heavy atom parameters t(J vary and using the diagnostic least-squarw nicttrotl (10). This method wxs not used for the refinement8 of the structural p:uwnc~t,c~rs:ts it \\-a~found that the initial struct~urc was not
rlow
mough
to
th
tinal
OIW
for t,lrcL
MICROWAVE
~PFXTRUM TABLR
H,CCHCOCl
4;55
VII
P.\n LMETERS :\ND PARTIAL REFINEMENT nv FITTING TO B .\NU C ROTATIONAL CONSTANTS
ASSUMED
STRUCTUR.~L
Parameter*
Heavy
OF s-TRANS
Assumed
Estimated SE
Refined
SE
atom 1.470 1.789 119.8 112.6 1.345 1.192 127.2
Ii (CC) IL(C-Cl) L c=c-c L C-C-Cl R (C=C, R (C=O) L c-c=0
0.01 0.02 1.8 3.0 0.01 0.02 3.0
1.476 1.816 122.6 116.3
0.01 0.02 1.5 1.0
Hydrogen” PR(C-H) R(C-H) L C=CH L C=C-H L C-C-H
1.086 1.084 121.5 120.0 117.4
(outer) (inner)
0
8 All distances are in A, all angles in degrees. s Uncertainties in the hydrogen parameters were not included when estimating the errors in the refined parameters since the calculated rotational constants are relatively insensitive to the hydrogen positions.
assumption that the rotational constants vary linearly with changes in the parameters to be valid. The most significant result of the fitting is the 3.7” increase in the C-C-Cl anglr and thr decrease in the estimated standard error in this angle from 3.0 t,o 1.O”. The refined angle is quite close to the C-C-H (aldehydic) angle of 115.2” (0.2”) 111acrolcin (I), which could have been an alternate initial estimate. It should be noted that the C-C-C angle also increases, by 2.8”, relative to the acrolein value. The opening up of both of these angles between the assumed and refined structures suggests that some increased repulsion between the vinyl group and the X atom of the CCOX group is introduced when the aldehydic hydrogen is replaced by chlorine. The results also indicate that the C-Cl bond length may bc slightly greater in s-trans acryloyl chloride than in acetyl chloride. Although this last conclusion is questionable it can be stated with confidence that the prosent work shows that the electron diffraction value for the C-Cl bond length of 1.74 (0.02)A is too low. The T’~substitution coordinates of the chlorine atom were calculated from the changes in the moments of inertia 1, and Ib on isotopic substitution. The coordinates arc 1 acl 1 = 1.085 (O.OOl)A and 1bcl 1 = 0.816 (0.005)B. The angle of rotation of the principal axes on isotopic substitut’ion is determined to be 2.3”.
KEWLEY,
4.56
HISMPHILL,
ANI)
CURL
(ii) Nuclear Quadrupole Coupling Constants The calculation of the quadrupolc principal axis elements xTZand xzlz,rcyuires a knowledge of the off diagonal element xd in addition to the c>xperimclntal xnu and xbbvalues. Unfortunately, in the present case the angle of rotation of principal inert,ial axes on isotopic subst,itution is too small and t,hr (‘rrors in thta “7c’1 species quadrupole coupling constants arc too large to allow a mc,aningful rstimate of Xab to be made. 111 interpreting the nuclear quadrupolc coupling constants of awtyl ChkJridc' Sirmot t (9) considered the rcsonancc st#ructurw
CRO@c/o-
H3C -
H$
I
\
CL
-
ci,
II
\
Ct+
Of
H,Cm
Ct
and deduced that the C-Cl bond has 9 ‘? double bond character and 41’ ‘G ionic character. It is of interest t#oconsider if replacement of the methyl group 1)~ thus vinyl group of s-trans acryloyl chloride favors the type II resonanw structuw because of conjugation of the H&=CH and C=Cl+ bonds. The affect \\ould cause loss of electron density from the chlorine, 3p, orbital and rcduw the: valw of_xZibelow the acetyl chloride value of xZZ= “1.6 (1) I\lHz. Thr c~xptrrimcntal value of 23.8 (0.2) l\$Hz for s-trans acryloyl chloride (see Table III) dors not indicate increased C-Cl double bond charactw but rather that the C:LCl bond is very similar in the two molecules. (iii)
Other Con_fomers
The observed dipole moment components of the s-trans form of 2.76 and 1.45 D when resolved in relation t’o thtl C-C single bond direction yield ~11 = 3.00 and pLI = 0.84 D. If as in acryloyl fluoride a vinyl group p,. rnornt>nt,(If about, 0.S D is present, directed towards t’he rest of the molecule, thaw it is most, reasonable to choose t’he direction of ~1as bet~wwn t’he C-Cl and C-O bonds and making an angle of 34.3” with the C-O direction, see Fig. 2. An approximate barediction of t’he dipole components and also th(, rotational constants of th(s s-cis form may be made by assuming the structure to be derived from the s-trans form solely by a 180” rotat’ion of the COCl group about the C-C single bond. The cxstimated quantities are pC(a = 2.7 L>, ,.L!,= 1.5 I), pCctot = 3.1 D, orientrd at’ 62’ to t,hcx carbon-oxygen bond and between the C=O and C--Cl directions, ,4 = 95X,5 AlHz, B = 2524 MHz, C = 1998 MHz and K = -0.861. The direction of the predicted dipole moment and principal a and b axes arc shown in Fig. 2. On this basis the “Ro,l type lines of the s-cis form falling in the 26.5-40 (;Hz range arc’ those of the J = .5 + 6, 6 --s 7 and 7 j s transitions. A consid~~rablr~
MICROWAVE
SPECTRUM OF s-TRANS H&CHCOCI
4.77
b
H
i.,.._._ __... ‘/ cc ;
Cl
c
pot
Cl
C-
H
\
/
0
‘a S-CIS
S -TRANS
(Predicted) FIG. 2. Dirertions of principal u and b inertia axes and electric dipole moment for s-trans acryloyl chloride together with the predicted directions for the a-& conformer. The total dipole moment is oriented at 27.7” to the principal Q-axis and at 33.3” to the C=O bond direction in the s-trans form. For t,hes-cis form the total dipole moment is predicted to make art angle of 33.7’ with t,he principal a axis and 62.3” with t,he C=O direction. amount of time has been used in trying to identify these peaks amongst the many strong lines of the s-trans form. An assignment has not yet been made even though a number of lines have bcrn studied in the 33-34 GHz range which show nuclear quadrupole hyperfine st,ructurc and are very likely not due to t,he s-trans form. In the infrared study (5) it was mentioned that there was no definite evidence that could rule out a skewed or gauche form as the less abundant conformer. Also in electron diffract,ion work on oxalyl chloride (15) the results at 0°C show that the gas is a, mixt,urc of s-trans and gauche conformers with t,he latter in 83 5%abundance. It may be that acryloyl chloride has a gauche conformer although this is not considrred very likely in view of the s-trans and s-cis conformers being found for acryloyl fluoride (.2). RECEIVED:
April
12, 1972 > REFER P’NCES
1. E. A. CHERNIAK AND C. C. C~STAIN, J. Cihcrn. Phys. 46,104 (1966). 8. J. J. KEIRNS AND R. F. CUBL, Jlt., J. ChmL. Phys. 48, 3773 (1968). 3. G. L. CARLSON, W. G. FATELEY, AND IL E. WITKOU’SKI, J. Aweer. Chevn. Sot. 89, 6437 (1967). /t. T. U~JI, Bull. Chew Sot. dap. (~~?ip~vn~u~a~~~ui) 30, 737 (1957). 5. J. E. KATON AND W. R. FEAIRHELLER, J. Chm. Phys. 47, 1248 (1967). 6. J. H. H@c, L. NYGAAED AND G. 0. SORENSEN, J. Mol. Stmct. 7, 111 (1970). 7. J. S. MUENTER AND V. W. LAUHE, J. Chcm. Ph,ys. 46,855 (1966). 8. J S. MUENTER, J. Chcm. Phys. 48, 4544 (1968). 9. K. M. SINNOTT,J. Chcm. Phys. 34, 851 (1961).
158
BEWLEY,
HEMPHILL,
ANI)
CURL
10. R. F. CURL, JR., J. Computational Phys. 6, 367 (1970). 11. L. PIERCE AND L. C. KRISHEH, J. Chem. Phys. 31, 875 (1959). 12. IL. W. &LB, C. C. LIN AND E. B. WILSON, JR., J. Chem. Phys. 26, 1695 (1957). 13. Ii. HEDBERG, Fourth Austin Symposium on (+as Phase Molecular Structure, The Un versity of Texas at Austin, 1972. Paper W2.