Facile synthesis, spectroscopic characterization and X-ray analysis of 4-alkoxylated 2-hydroxybenzophenones

Article abstract of DOI:10.1016/j.molstruc.2011.11.033

Two 2-hydroxy-4-alkoxy-3′-nitrobenzophenones were synthesized in a facile way. Their structures were characterized with the aid of mass spectra and ¹H NMR spectra analysis, as well as X-ray diffraction analysis. The ¹H NMR spectra sh

Full text of DOI:10.1016/j.molstruc.2011.11.033

Journal of Molecular Structure 1010 (2012) 79–84
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Facile synthesis, spectroscopic characterization and X-ray analysis
of 4-alkoxylated 2-hydroxybenzophenones
Lihua Lu a, Liang He b,c,
⇑
a College of Chemistry and Pharmaceutical Sciences, Qingdao Agricultural University, Qingdao 266109, PR China
b Engineering Research Center for Eco-Dyeing & Finishing of Textiles, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, PR China
c State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, PR China
a r t i c l e i n f o
a b s t r a c t
Two 2-hydroxy-4-alkoxy-30-nitrobenzophenones were synthesized in a facile way. Their structures were
characterized with the aid of mass spectra and 1H NMR spectra analysis, as well as X-ray diffraction analysis.
The 1H NMR spectra showed an intramolecular hydrogen bond formation in their structures. Compound 1
crystallizes in the monoclinic P2 (1) space group with the crystal cell parameters a = 3.9318(4) Å,
b = 7.1042(9) Å, c = 22.0400(19) Å,
Compound 2 crystallizes in the monoclinic space group P2 (1)/n with the crystal cell parameters
Article history:
Received 28 September 2011
Received in revised form 20 November 2011
Accepted 21 November 2011
Available online 9 December 2011
a = 90.00°, b = 92.3140(10)°, c
= 90.00°, V = 615.13(11) Å3 and Z = 2.
Keywords:
a = 3.9765(5) Å, b = 11.8286(15) Å, c = 28.867(3) Å,
a
= 90.00°, b = 92.8710(10)°,
c = 90.00°, V =
2-Hydroxybenzophenone
Spectroscopic characterization
X-ray analysis
Hydrogen bond
Stacking mode
1356.1(3) Å3 and Z = 4. Results showed that the benzophenone skeletons are non-planar, with a large tor-
sion to minimize their repulsive force. The substituted nitro or alkoxy groups are essentially coplanar with
respect to the benzene rings to which it connected, whereas the carbonyl group in benzophenone skeleton
is coplanar with the benzene ring which is substituted by alkoxy group. Classic and non-classic intra- and
intermolecular hydrogen bonds, together with the p–p stacking interactions stabilize their molecular con-
formations. The minor variations in the alkoxy group substituent cause great difference in their intermolec-
ular hydrogen bond formation and stacking mode.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
stabilizing dyes and pigments [8,9], as well as for synthesizing dis-
perse dyes as a built-in component [10,11].
Human skin needs to be protected against excessive radiation of
ultraviolet radiation (UVR) because UVR is the origin of premature
skin ageing, sunburns, allergies and even skin cancer. It is evident
that high levels of exposure to UVR increase the risk of three major
forms of skin cancer, with approximately 65–90% of melanomas
caused by UVR exposure [1]. In some countries, skin cancer is the
most common type of cancer and is increasing in incidence [2].
To protect skin against UVR, some measures recommended by
WHO including avoiding prolonged exposure to direct sunlight,
wearing sunglasses, using sunscreens, and use of loose-fitting
full-length clothes are very important and effective [3,4]. To pro-
duce merchants having anti-UVR functionality, UV absorbers hav-
ing intramolecular hydrogen bonding are widely employed [5,6].
2-Hydroxybenzophenone is a kind of typical UV absorber, which
can convert electronic excitation energy into harmless thermal en-
ergy via a fast, reversible, intramolecular proton transfer reaction
[7]. It is often used for preventing photodegradation of polymers,
The structural investigation of disperse dyes in solid state has
become an area of increasing research field [12–17]. Their absorp-
tion and dyeing behaviors are dependent not only on the confor-
mation of the solid dye but also on the interactions between
fiber surface and dye in molecular level [18]. Properties such as sol-
ubility and saturation value within fibres are related to the free
energy of dye molecule in crystalline state [19]. Accordingly, the
technical performance and functionality of disperse dyes have
strong relationship with their particle size, intra- and intermolecu-
lar interactions, morphology as well as crystal structure arrange-
ment [20]. X-ray studies of single crystals can effectively provide
full details of molecular structural information including intra-
and intermolecular interactions, which is very helpful to under-
stand their technical performance of the products.
As a series of research program for relationship between the
structure and function, we have reported the synthesis, spectral
and X-ray analyses of some azo and anthraquinone dye compounds
[21–24]. Expanding this interest, herein we describe a facile way to
synthesize two important UV absorbers based on 2-hydroxybenz-
ophenones (1 and 2, Fig. 1), which have reactive groups and can be
further functionalized based on requirements. In order to know
more structural details related to their use as UV absorber, their
⇑
Corresponding author at: Engineering Research Center for Eco-Dyeing
Finishing of Textiles, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou
310018, PR China.
&
E-mail address: lhedlut2002@yahoo.com.cn (L. He).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.11.033

80
L. Lu, L. He / Journal of Molecular Structure 1010 (2012) 79–84
O
OH
washing with 25 mL water and 5 mL acetone, it was dried at
50 °C. Then, the obtained cake was added to a mixture of 2.97 g
1-bromoethane, 2.47 g potassium carbonate and 0.16 g potassium
iodide in 30 mL acetone. The mixture was kept at 40 °C for 48 h.
After filtration, crude product was obtained and it was purified
by recrystallization from 1,2-dichloroethane to obtain 5.86 g of
yellow needles (81.5%). MS (API-ES Negative): m/z 286[MꢀH]ꢀ.
1H NMR (ppm, DMSO-d6): d = 1.35 (t, J = 6.8 Hz, –CH3), 4.12 (q,
J = 6.8 Hz, –CH2), 6.53 (d, J = 8.8 Hz, 1H), 6.56 (s, 1H), 7.45 (d,
J = 8.8 Hz, 1H), 7.83–7.86 (t, 1H), 8.08 (d, J = 8.0 Hz, 1H), 8.38 (s,
1H), 8.46 (d, J = 8.0 Hz, 1H), 11.48 (s, –OH).
O2N
O2N
1) SOCl2/chlorobenzene
HO OH
COOH
2)
3
OH
4
OCH3
OCH3
O
OH
O
OH
O2N
O2N
2.3. X-ray analysis
OC2H5
OCH3
Single crystal formation was achieved by dissolving the
2-hydroxybenzophenones in DMF at room temperature, and the
resulting solution was covered with a Parafilm plastic containing
pinholes and kept for several weeks, allowing slow evaporation
of DMF.
2
1
Fig. 1. Synthetic routes for the target 2-hydroxy-4-alkoxy-30-nitrobenzophenones
(1, 2).
The suitable each crystal was mounted on a nylon loop using
a small amount of Paratone N oil. All X-ray measurements were
made on a Bruker SMART diffractometer equipped with a graph-
ite monochromated Mo Ka (k = 0.71073) radiation source and a
CCD detector. The frame integration was performed using the
program SAINT [25]. The structures were solved by direct meth-
od provided by the program package SHELXTL-97 [26] and re-
fined a full matrix least square against F2 for all data. All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were introduced at idealized positions and were allowed to re-
fine isotropically. Crystallographic data of Compounds 1 and 2
are summarized in Table 1.
single crystal structures were also obtained and analyzed by X-ray
diffraction.
2. Experimental
2.1. General
m-Nitrobenzoic acid and resorcinol were provided by Sinop-
harm Chemical Reagent Co. Ltd. 1,3-Dimethoxy benzene, 1-bromo-
ethane and potassium iodide were from J&K Scientific Ltd.
Common reagent grade chemicals were commercially available
and were used without further purification. Mass Spectra were re-
corded on a HP 1100 MSD Mass Spectrometer (HP, US). 1H NMR
spectra were recorded on a Varian INOVA 400 MHz NMR spec-
trometer (Varian, US) using TMS as internal standard.
3. Results and discussion
3.1. Synthesis
2.2. Synthesis
During early stages of the synthesis, it was failed to prepare
2,4-dihydroxy-30-nitro-benzophenone (4) from resorcinol in the
solvent of 1,2-dichoroethane. Under this condition, resorcinol
was easily esterified by m-nitrobenzoic acid, whereas there was
almost no product of 4 obtained from the Friedel–Crafts acylation
reaction. Subsequently, 1-chlorobenzene was selected as the sol-
vent, in which the acrylation reaction of resorcinol ran smoothly.
2-Hydroxy-4-ethoxy-30-nitrobenzophenone (2) was synthesized
from the condensation of compound 4 with 1-bromoethane by
using potassium iodide as catalyst. In the condensation, the tem-
perature should be controlled strictly because the 2-position
hydroxyl group was easily alkylated by 1-bromoethane at higher
temperature. Similarly, compound 4 could be also used as starting
material to synthesize 2-hydroxy-4-methoxy-30-nitrobenzophe-
none (1) by alkylation. But, the effective methylating agents, such
as 1-iodomethane and dimethyl sulfate, were seldom used because
of their inappropriate properties. From another point of view, the
acrylation of 1,3-dimethoxy benzene by m-nitrobenzoic acid in
1,2-dichloroethane easily produced the intermediate, which was
hydrolyzed under acidic condition to produce absorber 1.
2.2.1. 2-Hydroxy-4-methoxy-30-nitrobenzophenone (1)
To the solution of 4.18 g m-nitrobenzoic acid in 10 mL
1,2-dichloroethane, 3.13 g thionyl chloride and catalytic amount
of DMF was added under stirring. The mixture was refluxed for
2 h. After cooled to room temperature, the resultant benzoyl chlo-
ride solution was added dropwise to the mixture of 3.34 g anhy-
drous aluminum chloride and 3.80 g 1,3-dimethoxy benzene in
30 mL 1,2-dichloroethane. After addition, it was heated to 70 °C
and kept for 5 h. After cooled to room temperature, the reactant
was poured into 100 g ice water containing 6 g hydrochloric acid
(35%). After stirring, the organic layer was collected by separation
and the solvent was removed under vacuum. Then the crude prod-
uct was purified by recrystallization from 1,2-dichloroethane to
obtain 5.95 g of yellow needles (87.1%). MS (APCI Negative): m/z
272.1[MꢀH]ꢀ, 308.1[M+Cl]ꢀ, 581.3[2M+Cl]ꢀ. 1H NMR (ppm,
DMSO-d6): d = 3.85 (s, –CH3), 6.55 (d, J = 9.2 Hz, 1H), 6.58 (s, 1H),
7.45 (d, J = 9.2 Hz, 1H), 7.81–7.83 (t, 1H), 8.07 (d, J = 7.6 Hz, 1H),
8.38 (s, 1H), 8.44 (d, J = 8 Hz, 1H), 11.45 (s, –OH).
2.2.2. 2-Hydroxy-4-ethoxy-30-nitrobenzophenone (2)
3.2. Spectral analysis
According to the method above-mentioned except using 1-chlo-
robenzene as solvent, the prepared m-nitrobenzoyl chloride solu-
tion was added dropwise to the mixture of 3.34 g anhydrous
aluminum chloride and 2.75 g resorcinol in 20 mL 1-chlorobenzene
at 80 °C. After addition, it was heated to 110 °C and kept for 5 h.
Then 15 mL water and 3 g hydrochloric acid (35%) were added.
The mixture was stirred at 100 °C for 1 h. After filtration and
The mass spectra of the 2-hydroxy-4-alkoxy-30-nitrobenzophe-
nones revealed the correct molecular ion peaks. It can be seen that
the base peaks of compound 1 corresponded to the de-protonated
specie generated using negative ion APCI. In this case, [MꢀH]ꢀ,
[M+Cl]ꢀ and [2M+Cl]ꢀ species were detected. Mass spectrometric
analysis of compound 2 worked better when negative API-ES was

L. Lu, L. He / Journal of Molecular Structure 1010 (2012) 79–84
81
Table 1
Crystallographic data for ortho-hydroxybenzophenones 1 and 2.
Data points
Absorber 1
14H11NO5
Absorber 2
Formula
C
C15H13NO5
287.26
0.36 ꢁ 0.07 ꢁ 0.05
Monoclinic
P2 (1)/n
Formula weight (g/mol)
Crystal dimensions (mm)
Crystal system
Space group
Temperature (K)
a (Å)
273.24
0.43 ꢁ 0.30 ꢁ 0.15
Monoclinic
P2 (1)
298(2)
298(2)
3.9318(4)
7.1042(9)
22.0400(19)
90.00
3.9765(5)
11.8286(15)
28.867(3)
90.00
b (Å)
c (Å)
a
(°)
b (°)
92.3140(10)
90.00
615.13(11)
1118
92.8710(10)
90.00
1356.1(3)
758
c
(°)
V (Å3)
Number of reflections to determine final
unit cell
Min and Max 2h for cell determination (°)
5.55, 49.362
5.462, 52.61
Z
2
4
F(000)
284
600
q
(g/cm)
k (Å) (MoK
(cmꢀ1
1.475
0.71073
0.114
1.407
0.71073
0.107
a)
l
)
Diffractometer Type
CCD area detector
CCD area detector
Scan type(s)
Phi and omega scans
Phi and omega scans
Max 2h for data collection (°)
Measured fraction of data
Number of reflections measured
Unique reflections measured
Rmerge
50.02
0.989
3052
1184
0.0391
1184
50.04
0.996
6259
2386
0.1465
2386
Number of reflections included in
refinement
Cut off threshold expression
Structure refined using
Weighting scheme
>2sigma(I)
>2sigma(I)
Full matrix least-squares using F2
Full matrix least-squares using F2
Calc w = 1/s2(Fo2) + (0.0693 P)2 + 0.0000 P where
Calc w = 1/s2(Fo2) + (0.0693 P)2 + 0.0000 P where
P = (Fo2 + 2Fc2)/30
182
P = (Fo2 + 2Fc2)/30
192
Number of parameters in least-squares
R1
0.0452
0.1085
wR2
0.1074
0.2271
R1 (all data)
wR2 (all data)
GOF
0.0639
0.1183
1.066
0.2357
0.2736
1.061
Maximum shift/error
0.000
0.000
Min & max peak heights on final
(e-/Å)
D
F Map
ꢀ0.165, 0.173
ꢀ0.423, 0.428
8
1
O
C
OH
4
6
O2N
1
3
7
5
OCH2CH3
10
2
9
4
6
2
3
5
7
10
9
8
1
Fig. 2. H NMR spectrum for 2-hydroxy-4-ethoxy-30-nitrobenzophenone (2) in DMSO-d6. The inset is the enlarged part of the aromatic protons.

82
L. Lu, L. He / Journal of Molecular Structure 1010 (2012) 79–84
used as the ionization method. A representative 1H NMR spectrum
of compound 2 is given in Fig. 2. The spectrum contains a triplet at
d 1.35 ppm and a quartet at d 4.12 ppm, with the coupling constant
of 6.8 Hz, for CH2 and CH3 group, respectively. The doublets at d
6.53 and 7.45 ppm arise from H2 and H3, while doublets at d 8.08
and 8.46 ppm arise from H5 and H7. The two singlets at d 6.56
and 8.38 ppm are assigned to H1 and H4, and the 1H triplet at d
7.83–7.86 ppm is assigned to H6. The 1H singlet at d 11.45 ppm
is attributable to the OH group, which shows the formation of an
intramolecular H-bond. This result is consistent with its nature
as a type of UV absorber.
Table 3
Selected bond lengths (Å) and bond angles (°) for 2.
N1–O4
N1–O5
N1–C12
O1–C1
O2–C3
O3–C5
O3–C8
C1–C2
C1–C10
C2–C7
C2–C3
1.228(8)
1.215(7)
1.497(9)
1.261(7)
1.353(7)
1.351(7)
1.445(8)
1.459(8)
1.495(9)
1.407(9)
1.416(8)
C3–C4
C4–C5
C5–C6
C6–C7
1.363(8)
1.371(9)
1.400(9)
1.384(9)
1.516(9)
1.410(9)
1.417(8)
1.355(9)
1.381(9)
1.368(9)
1.367(9)
C8–C9
C10–C11
C10–C15
C11–C12
C12–C13
C13–C14
C14–C15
O5–N1–O4
O5–N1–C12
O4–N1–C12
C5–O3–C8
O1–C1–C2
O1–C1–C10
C2–C1–C10
C7–C2–C3
C7–C2–C1
C3–C2–C1
O2–C3–C4
O2–C3–C2
C4–C3–C2
C3–C4–C5
O3–C5–C4
123.1(7)
O3–C5–C6
C4–C5–C6
C7–C6–C5
C6–C7–C2
123.0(6)
118.3(7)
118.5(7)
119.5(5)
120.6(6)
116.5(6)
122.9(6)
117.0(6)
122.4(6)
120.5(6)
117.8(6)
121.3(6)
120.8(6)
121.0(6)
116.3(6)
120.6(6)
118.3(6)
122.1(6)
107.3(6)
117.8(6)
117.3(6)
124.8(6)
118.7(6)
123.7(7)
117.6(7)
118.7(7)
117.9(7)
121.1(7)
120.7(7)
3.3. X-ray of the crystal structures
The attempt to grow single crystals of the two compounds from
organic solvents such as ethanol, acetic acid, acetone, 1,2-dichoroe-
thane and toluene always afforded amorphous powder or needle-
shape crystals, none of which diffracted well enough to solve their
crystal structures. Acceptable yellow crystals suitable for X-ray
analysis were obtained by slow evaporation of their DMF solutions
after several weeks at room temperature. 2-Hydroxybenzophe-
none 1 crystallizes in space group P2 (1) and 2 crystallizes in space
group P2 (1)/n. The two compounds are characterized by the
monoclinic space group with one molecule in the asymmetric unit.
Compound 1 has 2 molecules per unit cell, while 4 molecules are
found per unit cell for compound 2, whose molecular volume is
over two times of the volume of compound 1. Their selected bond
lengths and angles were reported in Tables 2 and 3. Their crystal
structures were given in Figs. 3 and 4.
The two aromatic portions of both 1 and 2 are obviously non-
planar as evidenced by the large torsion angles of 50.5(5)°
(C2–C1–C9–C14) for 1 and ꢀ48.2(11)° (C2–C1–C10–C15) for 2.
Their torsion angles around the alkoxy group are also a little differ-
ent. For instance, in 1 the C8–O3–C5–C4 torsion is 7.2(6)°, whereas
in 2 the C8–O3–C5–C6 is 4.2(10)°. The carbonyl groups are essen-
tially coplanar with the alkoxy-benzene rings. Their dihedral
angles between the carbonyl group and C2–C7 are 5.6(6)° for 1
and ꢀ3.8(10)° for 2. But, they are largely twisted out of the nitro-
benzene rings with the torsions of 45.7(5)° (O1–C1–C9–C10) for
1 and ꢀ46.7(10)° (O1–C1–C10–C11) for 2. For the nitro groups,
O3–C8–C9
C11–C10–C15
C11–C10–C1
C15–C10–C1
C12–C11–C10
C11–C12–C13
C11–C12–N1
C13–C12–N1
C14–C13–C12
C15–C14–C13
C14–C15–C10
they are slightly twisted out of the aromatic plan to which it
connected. The torsion angles of O4 and O5 are 7.6(6)° and
6.7(6)° for 1, and ꢀ5.7(11)° and ꢀ9.5(11)° for 2, respectively. Nitro
groups in some 4-nitroaozbenzene derivatives often show essen-
tial co-planarity with the adjacent aromatic ring by forming
intramolecular H-bonds between their oxygen atoms and the
nearby aromatic protons [27–29]. So the slightly larger twisted
conformations of nitro groups for both molecules are, at least in
part, due to the formation of intermolecular H-bonds of the oxygen
atoms, as listed in Tables 4 and 5. It can be seen that it exists three
kinds of unconventional C–Hꢂ ꢂ ꢂO H-bonds for 1 and two kinds of
unconventional H-bonds for 2. These intermolecular H-bonds have
bond length ca. 2.5–2.7 Å. It is interesting to note that O4 in 2,
Table 2
Selected bond lengths (Å) and bond angles (°) for 1.
N1–O4
N1–O5
N1–C11
O1–C1
O2–C3
O3–C5
O3–C8
C1–C2
C1–C9
C2–C7
C2–C3
1.205(5)
1.208(5)
1.469(5)
1.245(4)
1.343(4)
1.363(5)
1.426(5)
1.445(5)
1.507(5)
1.406(5)
1.413(4)
C3–C4
C4–C5
C5–C6
C6–C7
C9–C10
C9–C14
C10–C11
C11–C12
C12–C13
C13–C14
1.393(5)
1.373(5)
1.395(5)
1.360(5)
1.394(5)
1.387(5)
1.379(5)
1.375(5)
1.370(6)
1.377(5)
O4–N1–O5
O4–N1–C11
O5–N1–C11
C5–O3–C8
O1–C1–C2
O1–C1–C9
C2–C1–C9
C7–C2–C3
C3–C2–C1
O2–C3–C4
O2–C3–C2
C4–C3–C2
C5–C4–C3
O3–C5–C4
122.7(4)
O3–C5–C6
C4–C5–C6
C7–C6–C5
C6–C7–C2
114.7(3)
Fig. 3. ORTEP drawing of 2-hydroxy-4-methoxy-30-nitrobenzophenone (1) showing
numbering scheme.
119.1(3)
118.2(4)
118.1(3)
121.9(3)
116.6(3)
121.5(3)
116.7(3)
120.0(3)
117.4(3)
121.9(3)
120.7(3)
119.7(3)
124.1(3)
121.2(3)
118.6(3)
123.0(3)
123.3(3)
119.1(3)
117.4(3)
118.7(3)
122.2(3)
119.7(3)
118.0(3)
118.5(3)
120.7(4)
120.6(4)
C14–C9–C1
C14–C9–C10
C10–C9–C1
C11–C10–C9
C12–C11–C10
C12–C11–N1
C10–C11–N1
C13–C12–C11
C12–C13–C14
C13–C14–C9
Table 4
Intra- and intermolecular H-bonds geometry (Å, °) for 1.
D–Hꢂ ꢂ ꢂA
D–H
Hꢂ ꢂ ꢂA
Dꢂ ꢂ ꢂA
D–Hꢂ ꢂ ꢂA
O2–H2ꢂ ꢂ ꢂO1
0.82
0.93
0.93
0.93
1.840
2.534
2.574
2.697
2.562(4)
3.406(5)
3.332(6)
3.374(6)
146.11
156.31
138.88
130.42
a
C6–H6 ꢂ ꢂ ꢂO1
C14–H14bꢂ ꢂ ꢂO4
c
C12–H12 ꢂ ꢂ ꢂO5

L. Lu, L. He / Journal of Molecular Structure 1010 (2012) 79–84
83
Table 5
OꢀHꢂ ꢂ ꢂO H-bond, which is the origin of their use as UV absorbers.
The Hꢂ ꢂ ꢂO distance in 1 is 1.840 Å, whereas in 2 the Hꢂ ꢂ ꢂO distance
is 1.828 Å, the shorter interaction indicating an easier formation of
the intramolecular H-bond.
The structural influence around the alkoxy group has another
difference. The bond lengths of N1–O4, N1–O5 and N1–C11 for 1
are 1.205(5) Å, 1.208(5) Å and 1.469(5) Å, while the corresponding
bond lengths for 2 are 1.228(8) Å, 1.215(7) Å and 1.497(9) Å. This
indicates that in 1 the lone electron pairs in the N and the O atoms
Intra- and intermolecular H-bonds geometry (Å, °) for 2.
D–Hꢂ ꢂ ꢂA
D–H
Hꢂ ꢂ ꢂA
1.828
2.506
2.630
Dꢂ ꢂ ꢂA
2.556(7)
3.416(8)
3.451(1)
D–Hꢂ ꢂ ꢂA
147.29
166.34
147.47
O2–H2ꢂ ꢂ ꢂO1
0.82
0.93
0.93
a
C15–H15 ꢂ ꢂ ꢂO2
C13–H13bꢂ ꢂ ꢂO5
more delocalize to the bond systems and
p electron systems,
resulting in a larger double bond trend of these bonds compared
with those for 2. On the other aromatic portion, the bond length
of O3–C5 for 1 is 1.363(5) Å, which is longer than that bond for
2, with a value of 1.351(7) Å. This shows that for 1 the lone electron
pairs in O3 less delocalize to the
p electron system of the aromatic
ring. Considering their structural factors, these differences
between 1 and 2 should be caused by the greater electron-donating
capacity of the ethoxy group.
In network stacking of the two compounds, it is observed that
there are differences in the way of their H-bonds formation and
aromatic p–p stacking interactions (Figs. 5 and 6). In their stacking,
they include the head-to-head mode of molecular stacking (top fig-
ures). In such a way the head-to-head mode in 1 is in parallel
stacked, whereas this mode in 2 is in anti-parallel stacking. This
difference results from the molecular stacking stabilized by their
different formation of intermolecular H-bonds, as shown at the
bottom in Figs. 5 and 6. In 1, both O4 and O5 in nitro group partic-
Fig. 4. ORTEP drawing of 2-hydroxy-4-ethoxy-30-nitrobenzophenone (2) showing
numbering scheme.
unlike O5, does not participate in any C–Hꢂ ꢂ ꢂO interaction, which
may have influences on its molecular stacking mode. At the same
time, both molecules have a type of conventionally intramolecular
c
ipate in the formation of intermolecular H-bonds with H12 and
H14b in the different nitro-benzene rings adjacent to it. And O1
Fig. 5. Packing arrangement (top) and intermolecular interactions (bottom) by H-bonds for 2-hydroxy-4-methoxy-30-nitrobenzophenone (1).

84
L. Lu, L. He / Journal of Molecular Structure 1010 (2012) 79–84
Fig. 6. Packing arrangement (top) and intermolecular interactions (bottom) by H-bonds for 2-hydroxy-4-ethoxy-30-nitrobenzophenone (2).
in carbonyl group also forms H-bond in its parallel direction with
Acknowledgments
a
H6 in the nearby methoxy-benzene ring. However, in 2, only O5
in nitro group participates in the H-bonds formation with H13b
of its adjacent nitro-benzene ring in a way of head-to-head, which
forms a dimer. These dimers stack to form networks stabilized by
The work is financially supported by Zhejiang Top Academic
Discipline of Applied Chemistry and Eco-Dyeing & Finishing (No.
YR2010008).
a
the intermolecular H-bonds between O2 and H15 in its adjacent
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