Synthesis, Raman spectrum, ab initio calculations, and structure of 3,7-dioxabicyclo[3.3.0]oct-1,5-ene

Article abstract of DOI:10.1016/j.molstruc.2004.09.036

The bicyclic bisether molecule 3,7-dioxabicyclo[3.3.0]oct-1,5-ene (DOBO) molecule has been synthesized in small quantities and has been shown to be analytically pure by NMR and mass spectra. The vapor-phase Raman spectrum has been analyzed and compared to the predicted spectra from DFT calculations. This spectrum further confirms the structure of the molecule and shows the skeleton of both rings to be planar with D_2h symmetry. Ab initio calculations were carried out to predict the bond distances and angles of the molecule, and these also showed the molecule to be planar.

Full text of DOI:10.1016/j.molstruc.2004.09.036

Journal of Molecular Structure 742 (2005) 161–164
www.elsevier.com/locate/molstruc
Synthesis, Raman spectrum, ab initio calculations, and structure
of 3,7-dioxabicyclo[3.3.0]oct-1,5-ene
Cornelia Mlyneka, Henning Hopfa, Juan Yangb, Jaan Laaneb,
*
a
¨
¨
Institut fur Organische Chemie, Technische Universitat, D-38106 Braunschweig, Germany
bDepartment of Chemistry, Texas A&M University, College Station, TX 77843-3255, USA
Received 1 September 2004; revised 24 September 2004; accepted 27 September 2004
Available online 2 March 2005
Abstract
The bicyclic bisether molecule 3,7-dioxabicyclo[3.3.0]oct-1,5-ene (DOBO) molecule has been synthesized in small quantities and has
been shown to be analytically pure by NMR and mass spectra. The vapor-phase Raman spectrum has been analyzed and compared to the
predicted spectra from DFT calculations. This spectrum further confirms the structure of the molecule and shows the skeleton of both rings to
be planar with D2h symmetry. Ab initio calculations were carried out to predict the bond distances and angles of the molecule, and these also
showed the molecule to be planar.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Raman; Vapor-phase; DFT calculation; Molecular structure; 3,7-dioxabicyclo[3.3.0]oct-1,5-ene
1. Introduction
has been synthesized before (see below), but we were
interested in studying its vibrational spectrum, structure,
and the nature of its ring-puckering motions. The ring-
puckering spectra of BCO are expected to be very
complicated, and because the vibrations do not have
much of dipole moment changes, they are expected to be
weak [1,2]. DOBO, on the other hand, will have a large
dipole moment change for the in-phase puckering, and its
spectra should be simpler as the planar form should be the
most stable.
We have previously reported [1] the vibrational spectra
and ab initio calculations for bicycle[3.3.0]oct-1,5-ene
(BCO). This molecule is structurally interesting in that the
two five-member rings can pucker in either the same or
opposite directions producing either cis (C2v) or trans (C2h)
structures. Because the barriers to inversion are small, the
vibrational spectra can be described quite well on the basis
of a planar (D2h) structure. Nonetheless, the spectra and ab
initio calculations both show the cis C2v conformation to be
the lowest energy form. The C2h trans form is slightly
higher in energy but still about 1 kcal/mole more stable than
the planar structure.
For this initial report only 15 mg of DOBO were
prepared and this only allowed its vapor-phase Raman
spectrum to be recorded. Because of the small amount of
sample, no other spectra were recorded. Together with ab
initio calculations, the Raman spectrum was used to
determine the symmetry and structure of the molecule.
In the present paper, we present the method of
preparation for 3,7-dioxabicyclo[3.3.0]oct-1,5-ene
(DOBO) as well as its Raman spectrum. This molecule
2. Experimental
Raman spectra of the DOBO vapor at a temperature of
250 8C were recorded using an Instruments SA JY-U1000
spectrometer and a Coherent Radiation Innova 20 argon ion
laser with excitation at 514.5 nm and 4 W laser power.
* Corresponding author. Tel.: C1 979 845 3352; fax: C1 979 845 3154.
E-mail address: laane@mail.chem.tamu.edu (J. Laane).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.09.036

162
C. Mlynek et al. / Journal of Molecular Structure 742 (2005) 161–164
A liquid nitrogen cooled charge-coupled device (CCD) was
used as the detector. The spectral resolution was 0.7 cmK1
with the CCD. The sample was contained in a high-
temperature Raman cell previously described [3]. The
sample pressure was about 700 Torr.
4. Computations
Ab initio calculations were carried out using the
GAUSSIAN 03 package at both the Moller–Plesser second-
order perturbation (MP2) and the density functional
(B3LYP) levels of theory with various basis sets. Energies
and structural parameters were calculated using the MP2
theory with the CC-pVTZ (triple zeta) basis set, while
the vibrational frequencies with both the infrared and
Raman intensities were obtained with the density func-
tional (B3LYP) method and the 6-311CCG** basis
set. The frequency scaling factors are 0.964 for the
2800–3000 cmK1 region and 0.985 for the region below
3. Synthesis
The title compounds was essentially prepared by the
route described by Ripoll [4], and this is shown in Scheme 1.
Thus the Diels–Alder adduct 3 was prepared by cycloaddi-
tion of tetraethyl ethylentetracarboxylate 2 (Lancaster
Chemicals) to anthracene 1. LiAlH4 reduction of 3 then
provided the tetraalcohol 4 which on heating in DMSO [5]
for extended periods of time was dehydrated to furnish the
bisether 5.
1700 cmK1
.
5. Results and discussion
Although the thermal fragmentation of 5 by high
temperature vacuum pyrolysis yielded the starting material
1 in quantitative yield, the isolated amounts of the title
compound 6 varied and were much smaller. We believe that
this was due to the design of our pyrolysis system the tube of
which was much longer than the one employed in the
original literature [4]. Contact time was hence longer and
material lost by subsequent thermal reactions. The bisether
was purified in a two-step approach: filtration over silica gel
with pentane first allowed the removal of anthracene,
and after 6 had been isolated from the column by ether
extraction it was purified by vacuum sublimation (50 8C,
15 Torr). MS and NMR analysis showed the material to
be analytically pure (1H NMR (200.1 MHz, CDCl3): dZ
4.54 (s).K13C NMR (50.3 MHz, CDCl3): dZ70.15 (t),
141.67 (s).
Fig. 1 shows the vapor-phase Raman spectrum of 3,7-
dioxabicyclo[3.3.0]octane-1(5) (DOBO) recorded at 2508.
The sharp, more intense bands all correspond to the totally
symmetric Ag vibrations in D2h symmetry. The broader band
types correspond to B1g, B2g, and B3g modes. All other
vibrations are Raman inactive. Due to lack of sample, no
infrared spectra were recorded and thus the frequencies for
the infrared active ungerade modes were not determined
experimentally. Density functional theory (DFT) compu-
tations were used to calculate both the structure and Raman
spectrum of this molecule, and Fig. 1 also compares the
computated spectrum to the experimental one. The computed
spectrum assumes Lorentzian band shapes and therefore
makes no attempt to predict the vapor-phase band types. The
frequency agreement between the recorded spectrum and
calculated spectrum is excellent; the intensity agreement is
Fig. 1. Vapor-phase Raman spectrum of DOBO at 250 8C (top) and
calculated Raman spectrum using the B3LYP/6-311CCG** basis set
(bottom).
Scheme 1.

C. Mlynek et al. / Journal of Molecular Structure 742 (2005) 161–164
163
Table 1
Vibrational assignments (cmK1) for the Raman active (gerade) modes of 3,7-dioxabicyclo[3.3.0]oct-1,5-ene
Symmetry
D2h
v (D2h
)
Description
Raman
BCO vaporb,c
Ab initioa
Vaporb
D2h
b,d
CH2 sym. stretch (ip, ip0)
CaC stretch
CH2 deformation (ip, ip0)
CH2 wag (ip, op0)
Ring stretch
Ring breathing (ip0)
Ring bend (ip, ip0)
CH2 sym. stretch (op, op0)
CH2 deformation (op, op0)
CH2 wag (op, ip0)
Ring stretch
Ag
2870
1690
1486
1350
897
(100)
(4)
(100)
1
2
3
4
5
6
7
2857
1677
1473
1287
889
852
522
(2857)e
–
(100)
(27)
(17)
(5)
(22)
(14)
(7)
–
2887
1716
1501
1363
887
R:P
(5)
(10)
w
(8)
(0.7)
(2)
(7)
857
(2)
(0.2)
(1)
863
537
(4)
535
B1g
(2870)e
1469 sh
1385
–
(18)
(4)
8
9
2877
1488
1392
1235
1013
676
R:D
(4)
vw
(1)
w
–
–
–
(1)
10
11
12
13
1237
–
–
(0.8)
(0.2)
(0.3)
Ring stretch
Skeletal bend (op, op0)
1018
vw
vw
968
676
683
(1)
CH2 antisym. stretch (ip, op0)
CH2 twist (ip, ip0)
CH2 rock (ip, op0)
B2g
2902
1148
941
–
(5)
(2)
w
(10)
(2)
14
15
16
17
2954
(42)
2900
1130
932
R:D
–
–
–
–
–
–
(0.4)
(0.1)
Ring puckering (op0)
–
115
CH2 antisym. stretch (op, ip0)
CH2 twist (op, op0)
CH2 rock (op, ip0)
B3g
2886
1201
1071
450
(5)
(1)
vw
(2)
vw
–
(57)
(1)
18
19
20
21
2874
2899
1203
1074
449
R:D
–
–
–
–
(0.3)
(0.0)
Ring twisting (ip0)
–
ip, in-phase; op, out-of-phase; w, weak; v, very; sh, should; R, Raman; P, polarized; D, depolarized.
a
Calculated using the B3LYP/6-311CCG(d,p) basis set.
Relative intensity in parenthesis.
b
c
From Ref. [1].
Frequency scaled with a scaling factor of 0.985 for frequencies less than 1800 cmK1 and 0.964 for frequencies greater than 2800 cmK1
Frequency used twice.
d
.
e
Table 2
Calculated vibrational frequencies (cmK1) for the ungerade modes of 3,7-dioxabicyclo[3.3.0]oct-1,5-ene (DOBO) compared to bicyclo[3.3.0]oct-1,5-ene
(BCO)
Symmetry D2h
v (D2h
)
Description
Ab initioa
BCO (C2v)
b
c
DOBO (D2h
)
CH2 antisym. stretch (op, op0)
CH2 twist (op, ip0)
CH2 rock (op, op0)
Au
(0)
(0)
(0)
(0)
(47)
22
23
24
25
2898
1189
999
2896
1219
865
(0.86)
(0.37)
(0)
Ring twisting (op0)
209
191
CH2 antisym. stretch (ip, ip0)
CH2 twist (ip, op0)
CH2 rock (ip, ip0)
Ring flapping (ip0)
Ring puckering (ip0)
B1u
(54)
(19)
26
27
28
29
30
2901
1172
1025
166
2891
1217
1067
207
(1.6)
(2.8)
(0.78)
(8.7)
(2.5)
(1.6)
(4.2)
(0.05)
100
74
CH2 sym. stretch (op, ip0)
CH2 deformation (op, ip0)
CH2 wag (op, op0)
Ring stretch
B2u
(100)
(0.47)
(2.1)
(31)
(100)
(1.6)
31
32
33
34
35
36
2883
1493
1311
1069
1008
367
2864
1466
1305
1008
970
(1.6)
(0.57)
(0.02)
(1.1)
Ring stretch
Skeletal bend (op, ip0)
(27)
(0.61)
361
CH2 sym. stretch (ip, op0)
CH2 deformation (ip, op0)
CH2 wag (ip, ip0)
B3u
(8.2)
(0.57)
(8.4)
(1.0)
(20)
(43)
37
38
39
40
41
42
2881
1496
1375
1211
864
2860
1456
1316
1162
877
(1.4)
(0.40)
(0.11)
(0.29)
(0.45)
Ring stretch
Ring breathing (op0)
Ring bend (ip, op0)
(7.7)
785
658
ip, in-phase; op, out-of-phase.
a
Calculated using the B3LYP/6-311CCG(d,p) basis set.
Calculated relative infrared intensity in parenthesis. Frequency scaled with a scaling factor of 0.985 for frequencies less than 1800 cmK1 and 0.964 for
b
frequencies greater than 2800 cmK1
c
.
From Ref. [1].

164
C. Mlynek et al. / Journal of Molecular Structure 742 (2005) 161–164
6. Conclusions
The vapor-phase Raman spectrum of the DOBO
molcules is reported for the first time; it is in excellent
agreement with the computed spectrum and this further
verifies the molecular structure. Both the Raman spectrum
and ab initio calculations show that both of the rings for this
bicyclic molecule are planar.
In future work we hope to elucidate the nature of the
coupling between the puckering motions of the two rings.
Fig. 2. Structure of DOBO from the MP2 calculation (MP2/CC-pVTZ).
Acknowledgements
fairly good but certainly not close to perfect. Table 1 lists the
vapor-phase Raman frequencies for DOBO and compares
these to the BCO values. The DFT calculated vibrational
frequencies and intensities are also listed. The observed and
The authors wish to thank the National Science
Foundation (Grant CHE-0131935) and the Robert A.
Welch Foundation (Grant A-0396) for financial assistance.
This paper is dedicated to Walt Lafferty who preceded JL in
the R.C. Lord Spectroscopy Laboratory and helped to begin
the studies of large-amplitude vibrations with very non-
harmonic potential energy functions. His trimethylene oxide
work will be long remembered.
calculated frequencies agree on average within 9 cmK1
.
Table 2 lists the Raman inactive vibrations and their
DFT calculated frequencies for DOBO. These are also
compared to the experimental values of BCO. The
frequencies are fairly similar except that the ring modes
for DOBO are higher since C–O bond stretching force
constants are greater than those for C–C bonds. No
experimental data for the infrared active vibrations are
shown since there was not enough sample to record the
infrared spectra.
References
Fig. 2 shows the optimized structure for DOBO
from the MP2/CC-pVTZ (triple zeta) calculation. The
skeletal atoms, unlike the case for BCO which has
puckered rings, all lie within a plane resulting in D2h
symmetry. The recorded Raman spectrum, which shows
only the gerade vibrations, provides further evidence that
the molecule has D2h symmetry with a center of
symmetry.
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