Separation and crystal structure of two isomeric of 1,3,3-trimethyl-5- nitro-3-(4-nitrophenyl)-2,3-dihydro-1H-indene and 1,3,3-trimethyl-5-nitro-1-(4- nitrophenyl)-2,3-dihydro-1H-indene

Article abstract of DOI:10.14233/ajchem.2014.15410

The isomers, 1,3,3-trimethyl-5-nitro-3-(4-nitrophenyl)-2,3-dihydro-1H- indene (1) and 1,3,3-trimethyl-5-nitro-1-(4-nitrophenyl)-2,3-dihydro-1H-indene (2), have been prepared and separated effectively. Their crystal structures can not be confirmed by the r

Full text of DOI:10.14233/ajchem.2014.15410

Asian Journal of Chemistry; Vol. 26, No. 2 (2014), 399-402
http://dx.doi.org/10.14233/ajchem.2014.15410
Separation and Crystal Structure of Two Isomeric of 1,3,3-Trimethyl-5-nitro-3-(4-nitrophenyl)-
2,3-dihydro-1H-indene and 1,3,3-Trimethyl-5-nitro-1-(4-nitrophenyl)-2,3-dihydro-1H-indene
*
Y. WANG, D.F. WU, T. SHAO, J. MEN and G.W. GAO
Department of Chemistry, Sichuan University, Chengdu, P.R. China
*Corresponding author: Tel/Fax: +86 28 85412095; E-mail: gaoguowei@scu.edu.cn
Received: 2 March 2013;
Accepted: 9 May 2013;
Published online: 15 January 2014;
AJC-14552
The isomers, 1,3,3-trimethyl-5-nitro-3-(4-nitrophenyl)-2,3-dihydro-1H-indene (1) and 1,3,3-trimethyl-5-nitro-1-(4-nitrophenyl)-2,3-
dihydro-1H-indene (2), have been prepared and separated effectively. Their crystal structures can not be confirmed by the results of IR,
1H NMR, 13C NMR and MS studies, but determined by X-ray diffraction. The structure identity has explained the precise configurations
of title compounds. DSC/TG analysis illustrate that the isomers 1 and 2 possess excellent thermal stability.
Keywords: Indene, Aromatic nitration, Single structure, X-Ray diffraction.
were obtained from commercial sources and used without further
purification. Crystal structure determination was carried out
on a CAD4SDP 44 M/H diffractometer. IR spectra were
recorded on NEXUS 670 spectrometer with KBr pellets in
the 4000-400 cm-1 region. C, H, N and O elemental analyses
were performed with a Euro EA3000 apparatus. 1H and 13C
spectra were recorded at room temperature of 400 and 100
MHz, respectively. DSC analysis was implemented on a TA
Instrument DSC-Q100, TG on a TA Instruments TGA-Q500.
The data were recorded from room temperature to 500 ºC at a
heating rate of 20 ºC/min under N2 atmosphere.
INTRODUCTION
Bismaleimide (BMI) resins possess outstanding key prop-
erties such as high use temperature, thermooxidative stability,
high mechanical strength, high modulus, excellent electrical
properties and superior chemical resistance1,2. Recently, the
indene fragment has been developed by Ciba-Geigy company3
to design and synthetize novel bismaleimide resins. They
indicated that indene fragment features a rigid structure, a chiral
carbon atom and low melting point of the mixture of isomers
after nitration. The new findings decrease the melting point
and increase solubility of bismaleimide, not sacrifice their thermal
stability. The novel bismaleimides also reflect incredible stability
and mechanical properties. Terasaki et al.4 also introduced the
indene fragment into bisphenolA intermediates. However, they
haven’t supplied any compelling experimental evidence to illus-
trate those improvements of that designed fragment. The indene
fragment also kindles our interest in design some other novel
bismaleimides. Bismaleimides are usually obtained from conden-
sation of anhydrides and diamines5,6.Thetitlecompounds described
in this paper are precursors of diamines which are required for
bismaleimides synthesis. However, elemental analyses, IR,1H
NMR, 13C NMR and MS studies all failed to distinguish these
two isomers (Scheme-I). Herein, we separate the title isomers
effectively through general method and report the single crystal
structure to reveal the precise configuration of the title compounds.
O2N
NO2
1
HNO3/H2SO4
CHCl3
NO2
3
O2N
2
Scheme-I: Synthesis of compounds 1 and 2
General procedure: Compound 3 (23.6 g, 0.1 mol) and
chloroform (75 mL) were added to a 250 mL flask, after the
mixture was stirred and cooled down to 2-8 ºC, followed by
slow addition of a previously prepared solution of mixed acid
(HNO3 13.4 mL, H2SO4 39.6 mL). The process of the reaction
was monitored by using TLC analysis. Upon completion, the
reaction mixture was poured into ice water (300 mL). The
EXPERIMENTAL
1,3,3-Trimethyl-3-phenyl-2,3-dihydro-1H-indene (3) was
prepared according to reported procedure7,8. The other chemicals

400 Wang et al.
Asian J. Chem.
TABLE-1
CRYSTAL DATA AND STRUCTURE REFINEMENT FOR COMPOUND 1 AND 2
1
2
C18H18N2O4
326.34
Empirical formula
Formula weight
C18H18N2O4
326.34
Temperature (K)
291(2)
113(2)
Wavelength (Å)
0.71073
0.71073
Crystal system
Space group
Monoclinic
P21/c
Monoclinic
P21/n
Unit cell dimensions (Å)
a = 9.501(4)
b = 16.660(4)
c = 12.732(4)
β = 127.06(4)
1608.2(9)
a = 8.0246(16)
b = 29.435(6)
c = 13.328(3)
β = 90.92(3)o
3147.7(11)
8
(Å)
(Å)
(o)
Volume (Å3)
Z
4
Density (calculated) (g/cm3)
Absorption coefficient
F(000)
1.348
0.096
688
1.377
0.098
1376
Crystal size (mm3)
Theta range for data collection (o)
Index ranges
0.46 × 0.42 × 0.38
2.35-25.52
-11 ≤ h ≤ 11
-20 ≤ h ≤ 0
-10 ≤ h ≤ 15
3,214
0.20 × 0.18 × 0.12
2.06-25.02
-9 ≤ h ≤ 9
-21 ≤ h ≤ 35
-15 ≤ h ≤ 15
20,260
Reflections collected
Independent reflections
Data/restraints/parameters
Refinement method
2,985
5,540
2985/0/220
2985/0/220
Full-matrix least-squares of F2
0.975
R1 = 0.0509, wR2 = 0.1462
R1 = 0.1005, wR2 = 0.1679
-0.21/0.18
Full-matrix least-squares of F2
1.077
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
R1 = 0.0485, wR2 = 0.1102
R1 = 0.0556, wR2 = 0.1153
-0.22/0.25
∆ρmin/∆ρmax (e Å-3)
organic extracts were successively washed with 5 % NaHCO3
solution, dried over anhydrous MgSO4 and then evaporated
under reduced pressure. The yellow oil residue was purified
through a silica gel column chromatography to produce 25.2 g
(16.8 g + 8.4 g) (yield 77.3 %) of the title isomers 1 and 2.
Data of the two isomers are same unless specified (Table-1).
(m.p. 138-140 ºC) anal. calcd.(%) for C18H18N2O4: C, 66.25;
H, 5.55; N, 8.58. Found (%): C, 66.15, 66.25; H, 5.65, 5.87;
N, 8.58, 8.95. Main IR peaks (KBr, νmax, cm-1): 3066 (C-H),
1592 (C=H), 2963, 2923, 2866 (C-H), 1013 (C-H), 1518 (N-O).
1H NMR (CDCl3, 400 MHz, δ ppm): 1.11(s, 3H, Me), 1.43 (s,
3H, Me), 1.76 (s, 3H, Me), 2.34 (d, J = 12, 2H, -CH2-), 2.48
(d, J = 12, 2H, -CH2-), 7.22-7.32 (m, 3H, Ar-H), 8.09-8.19
(m, 4H, Ar-H). 13C NMR for 1 (CDCl3, 100 MHz, δ ppm):
156.92, 154.76, 154.06, 148.46, 146.31, 127.38, 125.54,
123.64, 123.95, 118.58, 58.95, 51.40, 43.22, 30.43, 30.28,
30.27. 13C NMR for 2 (CDCl3, 100 MHz, δ ppm): 159.62,
156.92, 149.17, 147.87, 146.31, 127.37, 123.81, 123.80,
123.67, 120.24, 58.85, 51.10, 43.44, 30.50, 30.23, 30.06.
gel column chromatography. We can not distinguish these two
isomers. According to IR, 1H and 13C NMR spectrum of 1 and
2, there is no obvious difference between the two compounds.
After analyzing the mixture’s 1H NMR spectrum (the residue
before purification by silica gel column chromatography), there
are two single-proton-peaks near the low field δ = 8 ppm and
the other proton shifts are all the some compared with the
1H NMR spectrum of 1 or 2. By classifying the proton shifts
of all the hydrogen atoms, it can be confirmed that the proton
peaks δ = 8.09 ppm and δ = 7.96 ppm are located in C17-H
(1, Fig. 2) or C14-H (2, Fig. 4). Mixture helps to increase the
split between C17-H (1) and C14-H (2) under the detection of
NMR. The ratio between the two proton peak areas is 1:1.79
(Sδ = 8.09 ppm/Sδ = 7.96 ppm), in Fig. 1, matching closely with the
ratio of 1 and 2 after purification by silica gel column chroma-
tography. However, those methods also can not help to distinguish
which one is 1 or 2. We turn to single-crystal X-ray diffraction
for help at last.
Structure description: Suitable crystals of 1 and 2 were
obtained by slow evaporation from methanol/CHCl3 solution
at room temperature.After analyzing by X-ray diffraction, we
can confirm that the major product is 2 finally. The molecular
structures of 1 and 2 are revealed in Figs. 2 and 4 and their
packing diagrams in Figs. 3 and 5.
As shown in Tables 2 and 3, the bond lengths and angles
in the 1 and 2 have normal values. In the title molecules, the
five-membered rings of the indene fragment adopt an envelope
conformation, while the flap atoms deviate by 0.5177(19) Å
(1) and 0.4329(30) Å (2) from the plane of the remaining
RESULTS AND DISCUSSION
Synthesis and separation: Nitration of 3 was achieved
with 2.2 equivalent of 65 % HNO3 and 7 equivalent of 98 %
H2SO4 at 0-15ºC. Upon completion, the residue contains very
small quality of mononitration compound. With the increase
of the ratio of the HNO3 and temperature, mononitration
product decreases, but the total yield of the title compounds
also decreases noticeably. Under the standard conditions, we
obtained 1 and 2 in ratio 1:2 or 2:1 after purification by silica

Vol. 26, No. 2 (2014)
Separation and Crystal Structure of Two Isomeric of (4-nitrophenyl)-2,3-dihydro-1H-indene 401
According to the Figs. 2 and 4, it can be seen that the
C15-nitro is farther from the nitrophenyl (C1-C6) than C16-
nitro. The dihedral angle of 2 between the phenyl ring (C1-C6)
and the indene benzene ring (C13-C18) 21.48º is greater than
that of 1. It is the torsion of the nitrophenyl, which helps reduce
the oppression of nitrophenyl on indene fragment and flap
atom of 2 deviates shorter than that of 1. In other words, we
can speculate, in the fragment of 3, that C16 holds greater
steric hindrance than C15 from the geometrical parameters
for the crystal structure of the title isomers9,10
.
8.25
8.20
8.15
8.10
8.05
8.00
7.95
ppm
Fig. 1. 1H NMR data for mixture of 1 and 2
Fig. 4. Molecular structure of the title regioisomer 2
From the crystal packing diagrams of 1 and 2, in Figs. 3
and 5, the molecule crystals are composed of dispersive
molecules hold together by van der Waals forces, without other
obvious intermolecular interactions. These non-covalent
interactions, in the title compound of 1 and 2, mainly come
from the diploe-dipole interaction of NO2-NO2 and the dipole-
induced dipole interaction of NO2-phenyl11.
Fig. 2. Molecular structure of the title regioisomer 1
Fig. 3. Packing diagram of regioisomer 1
four atoms (C10, C13, C18, C7), respectively. The dihedral
angles between the phenyl ring (C1-C6) and the indene benzene
ring (C13-C18) are 59.68(19)º(1) and 81.16(51)º(2), respec-
tively. C7, the chiral atom connects the indene ring and phenyl
ring, must be mentioned. Each angle of the four carbon atoms
(C6, C8, C9, C18) attached to C7(∠C6-C7-C9, ∠C6-C7-C8,
∠C8-C7-C9, ∠C8-C7-C18) is near close to 109.47º, the
standard angle of regular tetrahedron structure, which means
C7 dominates the twisty configuration of the title compounds
and enforces the molecules’rigidity. The indene benzene ring
forms dihedral angle of -33.47(08)º (1) and -29.14(20)º (2)
with the plane defined by the indene sp3-hybridized carbon
atoms C7, C9 and C10.
Fig. 5. Packing diagram of the title regioisomer 2
DSC-TG analysis: The thermal properties of the two
isomers, 1 and 2, have been investigated by DSC and TG
methods. Experimental data are shown in Table-4. The
absorption peaks of isomers 1 and 2 are all matched with their
melting-point. Especially, there are no any other absorption
peaks existing under 300ºC, which means no polymerization
or decomposition carrying out below 300ºC. The TG data show
that the isomers, 1 and 2 have excellent initial decomposition
temperature (T5 %), 221.2 ºC, 234.1 ºC and 234.1 ºC, respectively.

402 Wang et al.
Asian J. Chem.
TABLE-2
SELECTED BOND LENGTHS (Å)
AND ANGLES (º) BY X-RAY FOR 1
They also perform well in the maximal decomposition tempe-
rature (Tm), 287.6, 304.2 and 304.2 ºC, respectively. Those data
cited above illustrate that the isomers 1 and 2 possess excellent
thermal stability. It is concluded that the thermal properties of
material, in this paper, are mainly controlled by the rigidity or
configuration of the molecules and the existence of isomer
molecule.
Bonds
O1-N1
O2-N1
O3-N2
O4-N2
C3-N2
C3-C4
C6-C7
C7-C9
C7-C18
C9-C10
C10-C13
C14-C15
C15-C16
C15-N1
Dist.
Angle
(o)
1.210(3)
1.204(3)
1.225(3)
1.216(3)
1.469(3)
1.374(3)
1.532(3)
1.548(3)
1.514(3)
1.547(3)
1.524(3)
1.375(3)
1.372(3)
1.471(3)
O1-N1-O2
O1-N1-C16
O2-N1-C16
O3-N2-C3
O3-N2-O4
O4-N2-C3
C6-C7-C9
C6-C7-C8
C7-C9-C10
C7-C18-C17
C8-C7-C9
C8-C7-C18
C9-C10-C13
–
123.22(17)
118.37(16)
118.39(16)
118.68(16)
122.50(17)
118.82(18)
111.67(15)
108.79(15)
107.52(15)
128.06(16)
111.18(15)
110.44(15)
101.34(15)
–
Conclusion
1,3,3-Trimethyl-5-nitro-3-(4-nitrophenyl)-2,3-dihydro-
1H-indene (1) and 1,3,3-trimethyl-5-nitro-1-(4-nitrophenyl)-
2,3-dihydro-1H-indene (2) were separated successfully
through general method and characterized. Crystal structure
of 1 and 2 were determined by the X-ray single crystal diffrac-
tion analysis. In addition, the DSC-TG data show that the title
compounds have good thermal stability. These evidences conduct
us to design some other novel bismaleimide resins containing
the attractive indene fragment in the following work.
TABLE-3
SELECTED BOND LENGTHS (Å)
AND ANGLES (º) BY X-RAY FOR 2
ACKNOWLEDGEMENTS
The authors are grateful to Mr. Z.H. Mao of Sichuan Uni-
versity for the X-ray data collection. This work is supported
by Supported by Ministry of Education Project combining the
Industry and Teaching with Research of Guangdong Province
of China. (NO.2011B090400062).
Bonds
O1-N1
O2-N1
O3-N2
O4-N2
C3-N2
C3-C4
C6-C7
C7-C9
C7-C18
C9-C10
C10-C13
C14-C15
C15-C16
C15-N1
Dist.
Angle
(o)
1.210(3)
1.204(3)
1.225(3)
1.216(3)
1.469(3)
1.374(3)
1.532(3)
1.548(3)
1.514(3)
1.547(3)
1.524(3)
1.375(3)
1.372(3)
1.471(3)
O1-N1-O2
O1-N1-C15
O2-N1-C15
O3-N2-C3
O3-N2-O4
O4-N2-C3
C6-C7-C9
C6-C7-C8
C7-C9-C10
C7-C18-C17
C8-C7-C9
C8-C7-C18
C9-C10-C13
–
122.6(2)
118.7(2)
118.6(2)
117.8(3)
123.7(3)
118.5(3)
111.52(19)
109.14(19)
107.62(17)
127.6(2)
111.98(19)
112.34(19)
100.42(19)
–
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TABLE-4
DSC AND TG DATA OF ISOMERS, 1 AND 2
DSC TG
Compound
m.p. (ºC)
138-140
138-140
108-126
Tm (ºC)
143.8
143.8
121.3
T5 % (ºC)
234.1
234.1
Tmax (ºC)
304.2
304.2
1
2
Isomers
221.2
287.6