Raman, infrared, and microwave spectra and conformational preferences of meso-Bisoxirane

Article abstract of DOI:10.1016/S0022-2860(00)00437-3

Vibrational infrared and Raman spectra of liquid and solid meso-bisoxirane and infrared spectra of the gaseous phase were recorded. Additionally, microwave rotational spectra from 40 to 18 GHz were recorded. The vibrational spectra demonstrate the presence of two conformations in the fluid phases but only one in the solid state. Infrared and Raman activities and gas-phase band contours indicate that the trans conformer with C(i) molecular symmetry is more stable than the gauche conformer (C₁ symmetry). Variable temperature studies of two pairs of Raman lines are consistent with a ΔH value of 0.31 ± 0.10 kcal/mol in the liquid state. Rotational constants (A = 9187.45 ± 0.04, B = 2651.80 ± 0.01, C = 2608.92 ± 0.01 MHz) and the dipole moment (μ(total) = 3.03 D) were determined for the gauche conformer. Model calculations give an acceptable match to the observed rotational constants for an H-C-C'-H' dihedral angle of 60°. The relationship of meso-bisoxirane to other similar three-membered ring compounds is discussed. Published by Elsevier Science B.V.

Full text of DOI:10.1016/S0022-2860(00)00437-3

Journal of Molecular Structure 550–551 (2000) 521–530
www.elsevier.nl/locate/molstruc
Raman, infrared, and microwave spectra and conformational
ଝ,ଝଝ
preferences of meso-Bisoxirane
a,
b
c
c
*
V.F. Kalasinsky , S. Subramaniam , C.-F. Su , R.L. Cook
a
Department of Environmental and Toxicologic Pathology, Armed Forces Institute of Pathology, Washington, DC 20306, USA
b
Department of Chemistry, Mississippi State University, Mississippi, MS 39762, USA
c
Department of Physics and Astronomy, Mississippi State University, Mississippi, MS 39762, USA
Received 1 December 1999; accepted 8 February 2000
Abstract
Vibrational infrared and Raman spectra of liquid and solid meso-bisoxirane and infrared spectra of the gaseous phase were
recorded. Additionally, microwave rotational spectra from 40 to 18 GHz were recorded. The vibrational spectra demonstrate
the presence of two conformations in the fluid phases but only one in the solid state. Infrared and Raman activities and gas-
phase band contours indicate that the trans conformer with C molecular symmetry is more stable than the gauche conformer
i
(
C
1
symmetry). Variable temperature studies of two pairs of Raman lines are consistent with a DH value of 0:31 ^
0
0
:10 kcal=mol in the liquid state. Rotational constants ꢀA ˆ 9187:45 ^ 0:04; B ˆ 2651:80 ^ 0:01; C ˆ 2608:92 ^
:01 MHz† and the dipole moment ꢀm
ˆ 3:03 D† were determined for the gauche conformer. Model calculations give an
0 0
total
acceptable match to the observed rotational constants for an H–C–C –H dihedral angle of 60Њ. The relationship of meso-
bisoxirane to other similar three-membered ring compounds is discussed. Published by Elsevier Science B.V.
Keywords: meso-Bisoxirane; Raman, infrared and microwave spectra; Coformational preferences
1
. Introduction
activity [1,2]. An extensive study on d,l-bisoxirane
has been reported by Su et al. [3] in which rotational
constants, possible conformers and a vibrational
analysis of this molecule were discussed. The mole-
cule was shown to exist in predominantly two confor-
mers in the liquid and gaseous states. In the solid state,
it was found to exist in the more stable nearly trans
meso-Bisoxirane is a structural analog of bicyclo-
propyl (Fig. 1), with an oxygen atom substituted for
one of the carbons on each three membered ring. d,l-
Bisoxirane is its structural isomer, and both these
compounds have been shown to possess carcinogenic
0
0
conformer with an HC–H C dihedral angle near
90Њ. In the liquid phase, the nearly trans conformer
was found to be more stable than a nearly gauche
1
ଝ
Dedicated to Professor James R. Durig on the occasion of his
6
5th birthday.
0
0
ଝଝ
conformer (HC–C H ϳ40–50Њ) by 0.23 ^ 0.08 kcal/
mol. Rotational constants and dipole moment for the
nearly trans conformation were determined in the
gaseous state using microwave spectroscopy.
Disclaimer: The opinions and assertions expressed herein are
the private views of the authors and are not to be construed as
official or as representing the views of the Armed Forces Institute
of Pathology, the Department of the Army, or the Department of
Defense.
Even though d,l-bisoxirane has been well-charac-
terized, relatively little work has been reported on the
*
Corresponding author. Tel.: ϩ 1-202-782-2835; fax: ϩ 1-202-
7
82-9215.
0
022-2860/00/$ - see front matter Published by Elsevier Science B.V.
PII: S0022-2860(00)00437-3

5
22
V.F. Kalasinsky et al. / Journal of Molecular Structure 550–551 (2000) 521–530
that the trans isomer with C symmetry exists in the
i
solid state [4].
The measured values of dipole moments and molar
Kerr constants for meso-bisoxirane in solution [5] in
another study suggested that this molecule existed as a
mixture of trans and gauche conformers in solution. A
trans–gauche equilibrium in which the trans:gauche
ratio is approximately 20:80 was proposed. The
0
0
reported HC–C H dihedral angle of 60Њ for the
gauche conformer and the equilibrium ratio of the
gauche and trans conformers in the liquid phase can
be confirmed or refuted by using infrared, Raman, and
microwave spectroscopic data, but the data for meso-
bisoxirane are incomplete. Hence, this project was
undertaken to carry out a systematic vibrational and
rotational assignment and to determine the conforma-
tional stability of meso-bisoxirane.
2
. Experimental section
The preparation of meso-bisoxirane was carried out
in three steps as described in the literature [6].
Reagents were obtained from the Aldrich Chemical
Company. trans-l,4-Dibromo-2-butene was refluxed
with PbO in water to obtain trans-l,4-dihydroxy-2-
butene. The crude diol was purified by vacuum distil-
lation. The purified trans-2-butene-l,4-diol was
dissolved in dry ether, and bromine (in dry ether)
was added to obtain 1,4-dihydroxy-2,3-dibrombutane.
The product was dried under vacuum and recrystal-
lized with alcohol and hexane. Dehydrobromination
of 1,4-dihydroxy-2,3-dibromobutane was carried out
by using a suspension of KOH in anhydrous ether to
produce meso-bisoxirane. The product was purified by
trap-to-trap distillation with traps cooled to Ϫ76ЊC
and Ϫ196ЊC.
Raman spectra were recorded on a Spex Ramalog
DUV spectrometer equipped with a Spectra-Physics
Model 171 argon-ion laser operating at 488 nm.
Spectra of liquid samples were obtained after sealing
the samples in Pyrex capillary tubes, and spectra of
samples at low temperatures were recorded using a
Raman cell similar to one described by Miller and
Harney [7]. Temperatures were monitored with an
iron–constantan thermocouple and an Omega Engi-
neering model 199 digital thermometer.
Fig. 1. Conformations of (a) bicyclopropyl, (b) d,l-bisoxirane and
c) meso-bisoxirane.
(
isomeric form, meso-bisoxirane. The earliest report on
meso-bisoxirane indicated that two conformers exist
in the liquid and gaseous states while only the more
stable of these two conformers, which is the trans
isomer, was found in the crystalline state [4]. The
less stable form was presumed to possess C1
symmetry, and the trans isomer possesses C point
i
group symmetry. Only the gauche isomer with C1
symmetry can possess a permanent dipole moment
and, hence, molecular constants like principal
moments and rotational constants may be determined
for the gauche conformer using microwave spectro-
scopy. The infrared and Raman spectra of crystalline
meso-bisoxirane showed mutual exclusion confirming
Infrared spectra were obtained between 4000 and

V.F. Kalasinsky et al. / Journal of Molecular Structure 550–551 (2000) 521–530
523
Table 1
Ϫ1
Observed Raman and infrared frequencies (cm ) for meso-Bisoxirane
Raman
Liquid
Infrared
Gas
Assignments
Solid
Liquid
Solid
3
077 m
3077 m
CH
2
2
antisymmetric stretch
antisymmetric stretch
3
3
3
064 R
060 Q,s
052 P
3060 m
3076 w
CH
3
3
024 s
C–H stretch
3
010 vs
015 s,sh
CH
CH
CH
CH
2
2
2
2
symmetric stretch
symmetric stretch
deformation
3
3
3
012 R
006 Q,s
000 P
3000 s
3013 s
1
493 m
478 sh
1506 w
500 sh
1
1
deformation (gauche)
1494 R
1488 Q
1486 Q,w
1481 P
1480 m
1472 m
CH
2
deformation
1449 m
1421 m
1388 vw
1451 s
C–H bend
C–H bend (gauche)
C–H bend (gauche)
1425 vw
1382 Q,w
1418 m
1380 w
1
1
1
320 R
314 Q,m
308 P
1321 s
1307 s
1315 m
1263 m
C–H bend
1
1
268 s,sh
254 s
1265 Q
Ring breathing (gauche)
1262 vs
Ring breathing
1
250 vw,sh
1
1
259 R
250 P
1
250 m
150 w
1252 w
Ring breathing
1
1
200 vw
188 vw
1200 vw
1190 vw
CH
CH
2
twist
twist
1
158 Q vvw
148 Q,vvw
1159 s
2
1
1
1138 m
CH
CH
2
wag
wag
1
141 m
1146 w
2
1
142 sh
1
1
103 w
082 w
1100 vw
CH
C–H bend
2
wag (gauche)
1089 vw
1
077 Q
1075 vw
1030 w
1078 vw
C–H bend
C–H bend (gauche)
1
035 w
005 w
1031 Q
010 R
1003 Q,w
1
1
1000 w
C–H bend (gauche)
9
95 P
9
46 sh
9
40 m
938 m
Ring deformation (asymmetric)
Ring deformation (asymmetric)
Ring deformation (gauche)
Ring deformation (gauche)
9
39 Q,vvw
940 w,sh
910 s
943 w
913 vw
9
8
15 m
76 m
925 Q,vw
8
8
8
88 R
84 Q,s
76 P
875 vs
870 vs
858 vs
Ring deformation (symmetric)

5
24
V.F. Kalasinsky et al. / Journal of Molecular Structure 550–551 (2000) 521–530
Table 1 (continued)
Raman
Infrared
Gas
Assignments
Liquid
Solid
831 s
Liquid
842 sh
Solid
850 sh
830 m
807 m
Ring deformation (gauche)
Ring deformation (symmetric)
CH
CH
CH
2
2
2
rock (gauche)
8
8
8
32 R
27 Q,m
22 P
802 s
804 m
rock
7
91 m
82 m
rock
787 m
735 w
588 vw
7
C–C stretch
CH rock (gauche)
7
46 R
740 Q,s
730 m
580 m
2
7
5
33 sh
90 R
584 Q,w
C–C–O bend, out-of-plane
gauche)
(
5
5
83 Q
77 P
5
17 sh
5
12 w
74 w
513 w
C–C–O bend, out-of-plane
C–C–O bend, in-plane
4
70 R
4
465 Q,vw
470 m
(gauche)
4
60 P
4
2
08 m
58 w
408 s
C–C–O bend, in-plane
C–C–O bend, out-of-plane
(gauche)
1
50 vw
Lattice mode
Ϫ1
400 cm by using a Nicolet 7199 Fourier transform
measurements are accurate to 0.10 MHz or better.
For the Stark effect studies, the Stark cell was cali-
brated at high electric field with OCS, m ˆ 0.71521 D,
interferometer equipped with a KBr/Ge beamsplitter
and a liquid-nitrogen cooled mercury–cadmium–tell-
uride (MCT) detector. Spectra of the vapor were
obtained by placing the sample in a 12-cm, glass-
bodied, O-ring cell fitted with KBr windows, while
spectra of solid samples were obtained by using a
low-temperature cell which was equipped with a
cold finger attached to a brass block and cooled with
liquid nitrogen. Sample was sprayed onto a KBr
window, which was supported on the cold brass block.
The microwave rotational spectral lines presented
in this report were measured by using conventional
Stark-modulated Hewlett-Packard 8400 or 8460
microwave spectrometers in the X-, K-, and R-band
frequency regions. The measurements in the X-band
region were used only for the Stark effect studies. The
measurements were made at room temperature with a
sample pressure of 60 mtorr or less. The frequency
and at low fields with CF CCH, m ˆ 2.327 D.
3
3
. Results
Vibrational Assignments. Each conformer of meso-
bisoxirane possesses 30 normal vibrations. For the
more stable conformer with C symmetry, the prin-
i
ciple of mutual exclusion applies, so 15 are infrared
active and 15 are Raman active. The infrared active
A vibrations of this conformer will give rise to A-, B-,
u
C-type or hybrid band contours in the infrared spec-
trum of the gas. All 30 normal vibrations of the
gauche conformer (C1 symmetry) will be both
Raman and infrared active. The assignments of the
observed infrared and Raman spectra are shown in

V.F. Kalasinsky et al. / Journal of Molecular Structure 550–551 (2000) 521–530
525
Fig. 2. Raman spectra of (a) liquid meso-bisoxirane and (b) crystalline meso-bisoxirane. The marks indicate conformational peaks which
disappear during the crystallization process.
Table 1 and are consistent with those made for other
oxirane derivatives [3,8–11].
bands observed for the crystalline solid and are, there-
fore, assigned to the more stable conformer, while the
peaks that disappeared in going from the liquid to the
solid were assigned to the less stable conformer. In
comparing the Raman and infrared spectra of the crys-
talline solid, it is clear that the principle of mutual
exclusion holds as expected for Ci molecular
symmetry in the trans conformer [4]. (See Fig. 1.)
By contrast, the peaks assigned to the less stable
gauche conformer are generally coincident in the
Raman and infrared spectra as expected for C1
symmetry. Thus the peaks at 1478, 1421 (1418),
1388 (1380), 1268, 1103 (1100), 1035 (1030), 1005
(1000), 915, 876, 850, 807, 735 (730), 588 (580), 474
The infrared band contours are not particularly
helpful in making assignments or distinguishing
conformers because of the hybrid contours observed
in the spectrum of the vapor. The one exception is the
Ϫ1
B-type contour, with maxima at 1259 and 1250 cm ,
which corresponds to the infrared-active ring
breathing mode of trans-meso-bisoxirane.
The Raman and infrared spectra of liquid meso-
bisoxirane show bands corresponding to the two
conformers of this molecule. On cooling and subse-
quent solidification, several of the bands in the spectra
of the liquid and amorphous solid disappeared in the
crystalline solid (Figs. 2 and 3). The most intense
bands in the spectra of the liquid correspond to
Ϫ1
(470) and 258 cm in the Raman (or infrared) spec-
trum of the liquid state, which are absent from the

5
26
V.F. Kalasinsky et al. / Journal of Molecular Structure 550–551 (2000) 521–530
Ϫ1
Fig. 3. Infrared spectra of (a) gaseous, (b) amorphous, and (c) crystalline meso-bisoxirane in the frequency region between 3150 and 400 cm
.
The marks indicate conformational peaks which disappear during the crystallization process.
Ϫ1
spectra of the solid, were attributed to the gauche
conformer. The very weak feature at 913 cm in
the infrared spectrum is probably due to a small
number of gauche molecules remaining in an incom-
pletely annealed solid. The peaks in the liquid at 1268,
735, 588 and 474 cm were assigned to the ring
Ϫ1
0
breathing, CH rock, C CO bend (in-plane, out-of-
2
0
phase), and C CO bend (in-plane, in-phase), respec-
tively, for the gauche conformer and are candidates
for studying the conformational equilibrium.
Fig. 4. Microwave spectrum of meso-bisoxirane vapor from 21 to 19 GHz.

V.F. Kalasinsky et al. / Journal of Molecular Structure 550–551 (2000) 521–530
527
Table 2
Observed transition frequencies (MHz) of the ground vibrational state of gauche meso-Bisoxirane (calculated frequencies are obtained using the
spectroscopic constants in Table 3)
Transition
Observed
Obs.–Cal.
Transition
Observed
Obs.–Cal.
2
3
4
6
6
6
7
7
7
8
8
9
9
0
1
21 ← 111
22 ← 212
13 ← 303
06 ← 505
15 ← 514
24 ← 523
07 ← 606
16 ← 615
25 ← 624
35 ← 827
08 ← 716
37 ← 927
19 ← 827
37 ← 1029
38 ← 112,10
30213.54
35516.94
27814.85
31557.42
31691.87
31571.42
36183.44
36972.66
36835.57
32796.60
34890.00
32734.41
26700.03
32815.29
32829.63
36761.06
32848.26
32872.20
32902.15
32939.22
32984.45
33039.09
33104.61
33182.19
33273.50
33380.17
27344.89
31296.80
33646.91
39183.94
30745.54
33998.28
34211.20
39703.28
29297.94
28864.03
28401.96
27912.48
27396.30
26854.59
26288.27
25698.42
25086.50
24453.87
39750.26
22445.00
21029.21
19567.87
18075.86
0.07
Ϫ0.24
Ϫ0.10
0.30
0.37
0.30
Ϫ0.08
Ϫ0.02
Ϫ0.13
0.17
Ϫ0.31
Ϫ0.05
Ϫ0.37
0.16
0.10
Ϫ0.14
0.01
0.06
0.03
0.03
Ϫ0.02
0.08
2
3
5
6
6
6
7
7
7
8
9
9
9
20 ← 110
21 ← 211
14 ← 404
16 ← 515
25 ← 524
15 ← 505
17 ← 616
26 ← 625
07 ← 615
36 ← 826
36 ← 928
09 ← 817
18 ← 826
30171.02
35389.38
33184.18
31434.47
31564.32
38575.99
36672.32
36823.79
29794.27
32752.12
32304.52
39958.70
28585.59
32710.04
32677.81
39487.18
32635.69
32582.33
32515.77
32434.13
32335.76
32218.91
32081.54
31922.14
31739.02
31531.09
33504.06
28232.24
31035.21
33810.96
30427.24
30201.57
34452.10
34723.74
35028.54
35369.46
35749.42
36171.20
36637.88
37152.50
37718.12
38337.68
39014.22
23801.60
23131.47
21743.54
20303.28
18824.75
0.21
Ϫ0.22
0.03
0.26
0.55
Ϫ0.17
Ϫ0.02
Ϫ0.14
Ϫ0.21
0.10
0.20
0.05
Ϫ0.17
Ϫ0.19
Ϫ0.06
0.46
Ϫ0.11
Ϫ0.01
0.17
Ϫ0.06
Ϫ0.09
0.00
Ϫ0.05
Ϫ0.06
Ϫ0.17
Ϫ0.04
0.05
1
1
1
1
3
4
5
6
7
8
9
0
1
2
2
3
4
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
0
2
4
6
1038 ← 1028
1139 ← 1129
1
1,11 ← 1029
111,10 ← 1028
123 10 ← 122,10
133,11 ← 132,11
143,12 ← 142,12
153,13 ← 152,13
163,14 ← 162,14
173,15 ← 172,15
183,16 ← 182,16
193,17 ← 192,17
203,18 ← 202,18
213,19 ← 212,19
223,19 ← 222,21
232,21 ← 231,23
233,21 ← 232,21
243,21 ← 242,23
253,23 ← 252,23
252,23 ← 251,25
273,24 ← 272,26
283,25 ← 282,27
293,26 ← 292,28
303,27 ← 302,29
313,28 ← 312,30
323,29 ← 322,31
333,30 ← 332,32
343,31 ← 342,33
353,32 ← 352,34
363,33 ← 362,35
373,34 ← 372,36
383,36 ← 382,36
393,37 ← 392,37
413,39 ← 412,39
433,41 ← 432,41
453,43 ← 452,43
239 ← 122,11
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
4
4
4
4
3,10 ← 132,12
3,11 ← 142,13
3,12 ← 152,14
3,13 ← 162,15
3,14 ← 172,16
3,15 ← 182,17
3,16 ← 192,18
3,17 ← 202,19
3,18 ← 212,20
2,20 ← 221,22
3,20 ← 222,20
3,20 ← 232,22
2,22 ← 241,24
3,22 ← 242,22
3,22 ← 252,24
3,23 ← 262,25
3,25 ← 272,25
3,26 ← 282,26
3,27 ← 292,27
3,28 ← 302,23
3,29 ← 312,29
3,30 ← 322,30
3,31 ← 332,31
3,32 ← 342,34
3,33 ← 352,33
3,34 ← 362,34
3,35 ← 372,35
3,35 ← 382,37
3,38 ← 402,38
3,40 ← 422,40
3,42 ← 442,42
3,44 ← 462,44
0.00
Ϫ0.01
Ϫ0.01
0.01
Ϫ0.18
0.01
0.03
Ϫ0.05
0.07
Ϫ0.05
0.34
0.03
0.20
0.14
0.03
0.02
Ϫ0.05
Ϫ0.01
Ϫ0.06
Ϫ0.08
Ϫ0.01
Ϫ0.03
Ϫ0.05
Ϫ0.06
Ϫ0.04
Ϫ0.20
Ϫ0.12
Ϫ0.04
0.03
Ϫ0.12
Ϫ0.11
Ϫ0.05
Ϫ0.03
0.01
Ϫ0.04
0.03
Ϫ0.07
Ϫ0.01
0.01
Ϫ0.14
0.11
0.09
0.06
Ϫ0.03
Ϫ0.04
Ϫ0.05
Ϫ0.03
Ϫ0.03

5
28
V.F. Kalasinsky et al. / Journal of Molecular Structure 550–551 (2000) 521–530
In the solid state, some of the bands for the trans
conformer exhibit splitting probably due to the
presence of two or more molecules per unit cell in
Q-branch transitions ꢀJ3
← J
† would domi-
;JϪ2
2;JϪ2
nate in the K-band frequency region and that the
spacing between two adjacent lines would increase
very slightly as the frequency decreases and the rota-
tional quantum number increases. A portion of the
recorded low-resolution spectrum in K-band is
shown in Fig. 4. It is obvious that a number of strong
lines marked with arrows appear with approximately
even spacings. Preliminary analysis provided an
assignment of the thirteen lines observed in the K-
band frequency region for the rotational quantum
numbers from 34 to 46. Analysis of these lines gave
an improved set of rotational constants. Transitions of
the same series at higher frequency and transitions of
the crystalline solid. The pairs of bands in the infrared
Ϫ1
spectrum at 1320 and 1310 cm
and 875 and
Ϫ1
8
58 cm , for the C–H bend and a ring deformation,
respectively, are examples. Similarly the peaks at
Ϫ1
Ϫ1
1
200 and 1190 cm
and at 517 and 513 cm ,
0
assigned to the CH rock and C –C–O bend, are
2
observed in the Raman spectrum. Another pair of
Ϫ1
Raman lines, at 791 and 782 cm , might reflect
crystal splitting or two different fundamental vibra-
tions as indicated in Table 1, but it is impossible to
be certain.
Conformer Stability. The changes in intensity of the
another series ꢀJ3
← J
† were predicted, and
;JϪ3
2;JϪ1
Ϫ1
pairs of conformer peaks at 474 and 408 cm and at
these lines were measured and added to the analysis.
The observed Q-branch transitions could only be
used to determine two rotational parameters. R-
branch transition lines were needed to evaluate the
three rotational constants. The predicted spectrum
showed that two series of c-type, low-J, R-branch
transitions were in the K- and R-band frequency
Ϫ1
5
88 and 512 cm in the Raman spectrum of the
liquid were monitored over a temperature range
from 297K to 247K. These pairs showed changes in
peak area with changes in temperature. The van’t Hoff
equation for the determination of DH is given by:
0
lnꢀI=I † ˆ ϪꢀDH=R†ꢀ1=T† ϩ const:
regions. The series are J0;J ← ꢀJ Ϫ 1†
and
1;JϪ2
Using the intensity ratios and absolute tempera-
tures, plots of reciprocal temperature versus the
natural logarithm of intensity ratios for the aforemen-
tioned peak pairs were prepared. The slopes ꢀDH=R† of
the least-squares straight lines were 142:1 ^ 20:9 K
and 172:7 ^ 47:3 K for the lower- and higher-
frequency peak pairs, respectively. The average DH
value was found to be 0:31 ^ 0:10 kcal=mol:
Microwave spectra. The structural parameters used
for d,l-bisoxirane were used to predict the rotational
spectrum of meso-bisoxirane, and the dipole moment
of ethylene oxide was used to estimate its dipole
moment components. Because of symmetry, the
dipole moment components were found to be zero
in the trans form. Those of the gauche form, on the
other hand, were found to be substantial. Hence, the
rotational spectrum of the gauche form is expected in
the observations. Calculations indicate the gauche
Ϫf o 0r m: 98i 7s :a nearly prolate asymmetric rotor with k ˆ
J1;JϪ1 ← ꢀJ Ϫ 1†
: In each of the series, the
0;JϪ1
spacing between two adjacent lines was approxi-
mately B ϩ C. Additionally, the Stark behavior of
the transition lines for each series was expected to
be similar. After some searching, four lines of each
series were assigned and used to predict other
transitions.
Besides the c-type transitions, the weaker a- and b-
type R-branch transitions were also assigned and
included in the analysis. The 97 assigned lines listed
in Table 2 were used to evaluate the spectroscopic
constants. An effective rotational Hamiltonian
including the effects of centrifugal distortion was
employed [12]. The evaluated constants are listed in
Table 3. The spectral lines were fit with a standard
deviation of 0.15 MHz using these constants.
Due to a dense spectrum, only three rotational tran-
sitions listed in Table 2 were studied for the Stark
effect analysis. The Stark effect was found to be
second order. The Stark splittings and necessary para-
meters were used to determine the dipole moment
components by a least-squares fit method. The eval-
uated values are also listed in Table 4.
The calculated moments of inertia along with the
estimated dipole moment components indicate that
the c-type transitions would be the strongest and the
b-type ones the weakest. The predicted rotational
spectrum also indicated that a series of high-J
The structural parameters initially used to predict
the rotational transitions were adjusted slightly to

V.F. Kalasinsky et al. / Journal of Molecular Structure 550–551 (2000) 521–530
529
Table 3
Table 4
Spectroscopic constants (in MHz) for the ground vibrational state of
Dipole moment components of the ground vibrational state of
gauche meso-Bisoxirane
gauche meso-Bisoxirane
A ˆ 9187:45 ^ 0:04
B ˆ 2651:80 ^ 0:01
m ˆ 1:084 ^ 0:024 D
a
m ˆ 0:350 ^ 0:128 D
b
C ˆ 2608:92 ^ 0:01
m ˆ 2:808 ^ 0:049 D
c
Ϫ3
D ˆ ꢀϪ0:182 ^ 0:047† × 10
m ˆ 3:030 ^ 0:139 D
J
Ϫ1
D
ˆ ꢀϪ0:533 ^ 0:00011† × 10
Transition
|M|
2
1
1
1
K
Ϫ2
DJK ˆ ꢀϪ0:496 ^ 0:304† × 10
312 ← 202
312 ← 202
202 ← 101
505 ← 413
Ϫ4
d ˆ ꢀϪ0:441 ^ 0:0012† × 10
J
Ϫ3
d
K
ˆ ꢀϪ0:175 ^ 0:101† × 10
obtain a better agreement with the experimental
rotational constants. These are shown in Fig. 5.
Several assumed parameters were used. They are:
conformer present. d,l-Bisoxirane, which is a struc-
tural isomer of meso-bisoxirane, has been shown by
infrared and Raman studies to exist in a nearly trans
conformer and at least one nearly gauche form. The
dihedral angles (defined as the angle between the C–H
bonds of the two rings) for these two conformers in
d,l-bisoxirane were estimated to be 190 and 45Њ,
respectively. However, the trans conformer of meso-
bisoxirane is presumed to possess a dihedral angle of
0
0
˚
ЄHCH ˆ 120Њ, Є HCC 116Њ, C–H ˆ 1.09 A, and
0
0
ЄHCC H (dihedral angle) ˆ 65.5Њ. The rotational
constants based upon these structural parameters
are (in MHz) A ˆ 9173; B ˆ 2666; and C ˆ 2605:
These predicted rotational constants are very consis-
tent with those listed in Table 3.
4. Discussion
180Њ based on the molecular symmetry (C ) deter-
i
mined from the vibrational spectra and the lack of a
microwave spectrum, which implies a zero dipole
moment. The gauche conformer of meso-bisoxirane,
which exhibits the observed microwave spectrum,
was determined to possess a dihedral angle of
approximately 60Њ. The derived rotational constants
meso-Bisoxirane is known to exist as two different
conformers. Both the gauche and trans conformers
have been found to exist in the liquid and gaseous
states. In the crystalline solid state, the more stable
trans conformer with C symmetry is the only
i
Fig. 5. Assumed structure of gauche-meso-bisoxirane.

5
30
V.F. Kalasinsky et al. / Journal of Molecular Structure 550–551 (2000) 521–530
and dipole moments consistent with this structure are
shown in Tables 3 and 4.
meso-bisoxirane. These calculations are consistent
with the data which favor a trans conformer for
meso-bisoxirane, but this unfavorable interaction for
Two conformers of meso-bisoxirane have been
confirmed by the present study, and vibrational
bands corresponding to the more stable trans
conformer were found to be present in the solid
0
the gauche form can be minimized if the C –C–O
angle (or the tilt between the oxirane rings) is slightly
larger than originally assumed. From the diagrams in
Fig. 1, it is apparent that the dihedral angle is an
important factor in determining the non-bonded
0
0
state. The peaks corresponding to the CC O bends
of the gauche and trans conformers were monitored
in a variable temperature study of the liquid phase. It
was found that the trans conformer is more stable than
0
0
C ···O and O ···O distances. In meso-bisoxirane, a
dihedral angle of the order of 60Њ satisfactorily
achieves this balance, while a smaller dihedral angle
(40–50Њ) is necessary for d,l-bisoxirane as indicated
previously [3].
0
0
the gauche conformer (HC–C H 60Њ) by 0:31 ^
:10 kcal=mol: The corresponding enthalpy difference
0
for these conformer pairs is 0:23 ^ 0:08 kcal=mol in
d,l-bisoxirane [3].
Two conformers were considered in a study of the
solution polarizability of meso-bisoxirane [5]. Based
on the measured polarizability and molar Kerr
constants, the more abundant solution-state confomer
for meso-bisoxirane was predicted to be the gauche
conformer with the HC–C H dihedral angle of 60Њ.
The dihedral angle inferred in the present study was
found to be close to 60Њ for the gauche conformer
based on the microwave and infrared data, but the
gauche conformer is less stable than the trans. The
DH value for the liquid is small enough, though, that
the degeneracy of the gauche conformer might make
it the more abundant conformer.
References
[1] B.L. Van Dauren, L. Langseth, B.M. Goldschmidt, L. Orris, J.
Natl. Cancer Inst. 39 (1967) 1217.
[2] L. Otvos, I. Elekes, Tetrahedron Lett. (1975) 2481.
0
0
[3] C.F. Su, R.L. Cook, C. Saiwan, J.A.S. Smith, V.F. Kalasinsky,
J. Mol. Spectrosc. 127 (1988) 337.
[
[
4] W. Luttke, A. Demeijere, Tetrahedron Lett. (1966) 4149.
5] M.J. Aroney, K.E. Calderbank, H.J. Stootman, Aust. J. Chem.
27 (1974) 3194.
[6] W.F. Beech, J. Chem. Soc. (London) (1951) 2483.
[7] F.A. Miller, B.M. Harney, Appl. Spectrosc. 24 (1971) 291.
[8] V.F. Kalasinsky, C.J. Wurrey, J. Raman Spectrosc. 9 (1980)
4
5.
9] V.F. Kalasinsky, C.J. Wurrey, J. Raman Spectrosc. 9 (1980)
15.
[
Assumed structural parameters taken from d,l-
bisoxirane [3] were used to calculate distances
between nonbonded atoms for meso-bisoxirane as a
function of dihedral angle. If van der Waals radii [13]
3
[10] C.J. Wurrey, R. Krishnamoorthi, S. Pechsiri, V.F. Kalasinsky,
J. Raman Spectrosc. 12 (1982) 95.
[11] C.J. Wurrey, Y.Y. Yeh, R. Krishnamoorthi, R.J. Berry, J.E.
DeWitt, V.F. Kalasinsky, J. Phys. Chem. 88 (1984) 4059.
˚
of 1.7, 1.2, and 1.5 A for carbon, hydrogen, and
[12] W. Gordy, R.L. Cook, Microwave Molecular Spectra, 3,
Wiley, New York, 1984.
oxygen, respectively, are utilized, the only calculated
non-bonded distance which is less than the sum of the
[13] B.E. Douglas, D.H. McDaniel, J.J. Alexander, Concepts and
Models of Inorganic Chemistry, 2, Wiley, New York, 1983.
0
appropriate radii is the C ···O distance in gauche