Structural investigations of 3-acetamido-4-nitrobenzal derivatives

Article abstract of DOI:10.1016/S0022-2860(01)00623-8

N-(p-dimethylaminophenyl)-α-(3acetamido-4-nitrophenyl)nitrone (I) and 3-acetamido-4-nitrobenzylpyridinium bromide (II) were synthesized and their crystal structures were determined by X-ray diffraction methods. The geometry of carbon-nitrogen bond in nitrone is trans. In I the acetamido moiety slightly deviates from plane to the rest of molecule. The intramolecular N-H···O and C-H···O as well as intermolecular C-H···O hydrogen bonds stabilize the crystal structures of both the compounds. NMR investigations of II have given spectra with extra signals in comparison to the number of expected that suggests that dominating structure of this compound observed in crystal state coexists in solution with comparable amount of the additional form due to an interaction with solvent and increasing conformational freedom. For II duplication of signal number is observed for the 3-acetamido-4-nitrobenzyl substituent due to formation only of two different edge to face structures of this compound in DMSO and D₂O solution. For I in DMSO solution the major form has perpendiculair orientation of N,N-dimethylaniline substituent on nitrone bond against the plane containing the rest of the molecule.

Full text of DOI:10.1016/S0022-2860(01)00623-8

Journal of Molecular Structure 597 .2001) 241±257
www.elsevier.com/locate/molstruc
Structural investigations of 3-acetamido-4-nitrobenzal derivatives
*
G. Rusek, I. Bryndal, B. Picur , T. Lis, I. Brzostowska
Faculty of Chemistry, University of Wrocøaw, F Joliot-Curie 14, 50-383 Wrocøaw, Poland
Received 7 March 2001; revised 19 March 2001; accepted 10 April 2001
Abstract
N-.p-dimethylaminophenyl)-a-.3acetamido-4-nitrophenyl)nitrone .I) and 3-acetamido-4-nitrobenzylpyridinium bromide
.II) were synthesized and their crystal structures were determined by X-ray diffraction methods. The geometry of carbon±
nitrogen bond in nitrone is trans. In I the acetamido moiety slightly deviates from plane to the rest of molecule. The
intramolecular N±H´´´O and C±H´´´O as well as intermolecular C±H´´´O hydrogen bonds stabilize the crystal structures of
both the compounds.
NMR investigations of II have given spectra with extra signals in comparison to the number of expected that suggests that
dominating structure of this compound observed in crystal state coexists in solution with comparable amount of the additional
form due to an interaction with solvent and increasing conformational freedom. For II duplication of signal number is observed
for the 3-acetamido-4-nitrobenzyl substituent due to formation only of two different edge to face structures of this compound in
DMSO and D2O solution. For I in DMSO solution the major form has perpendicular orientation of N,N-dimethylaniline
substituent on nitrone bond against the plane containing the rest of the molecule. q 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Crystal structure; Nitro group; Inter- and intramolecular hydrogen bonds; Nitrones as amide isomers; Conformational equilibria by
NMR; Edge to face interaction
1. Introduction
fact that nitrone moiety
Investigations of substituted benzyl derivatives
have been continued in our group for several years
[1±3]. In this paper we present synthesis route and
structure determination of the N-.p-dimethylamino-
phenyl)-a-.3acetamido-4-nitrophenyl)nitrone using
the 3-acetamido-4-nitrobenzylpyridinium bromide.
Easy direct ways to obtain such substituted benzalde-
hydes are not known. Nitrones raise a possibility to
obtain them in a blocked form with a good yield.
Another aspect of this investigation is linked to the
is isomeric to the amide bond and very similar to the
one .charged) from two resonance expressions of this
group:
*Corresponding author. Tel.: 148-71320-4230; fax: 148-71328-
2348.
E-mail address: bp@wchuwr.chem.uni.wroc.pl .B. Picur).
0022-2860/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-2860.01)00623-8

242
G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
a minor quantity. The crystal structures of the title
compounds were determined as a part of studies on
the in¯uence of the nitro group position on the mole-
cular structure of molecules investigated. Crystal
structure of the intermediate 3-acetamido-4-nitroben-
zylpyridinium bromide .Scheme 2) was also deter-
mined. The structure of the 4-nitro and 6-nitro
isomer has been described previously [1,3].
Route of reactions is shown in Scheme 3.
2. Experimental
Scheme 1.
2.1. Synthesis
2.1.1. 3-Acetamido-4-nitrotoluidine
The substitution of amide bond by isomeric .pepti-
domimethic) nitrone group should give interesting
compounds possessing different charge distribution
and reactivity. In the course of investigation we
were led by the properties of natural aminoacid N-
methyl-4-aminoproline isolated lastly from linen [4].
The oxidation of this residue gave planar bond
To a stirred solution of m-toluidine .0.1 mol) [7] in
acetic anhydride .73.5 cm3) copper.II) nitrate trihy-
drate .0.05 mol) was gradually added at 1±58C. The
reaction mixture was stirred for 24 h, then poured into
ice and stirred until acetic anhydride disappeared.
Precipitated brown solid was ®ltered off and washed
until all copper salts were removed. Crude solid was
dissolved in concentrated sulphuric acid [8] and then
diluted with equal amount of water. The obtained
solution was heated on steam bath for 5 h, cooled
and diluted with water until no more precipitates
were formed. Precipitate was ®ltered off and carefully
washed and dried in air. Crude solid was dissolved in
acetic anhydride after gently heating on heating
mantle, and then the mixture was left to cool.
Obtained crystals were recrystallized from ethyl
acetate .6.39 g, mp 84.5±85.58C, the earlier reported
in pyrolidyne ring with positively charged atom of
nitrogen similar to the one in nitrone planar group ±
CHyN1.O2)±. This similarity gives present work on
nitrones a new importance in search of the synthetic
pharmaceuticals like immunosupressant and anti-
pathogen drugs [5].
This work is also connected to peptide area by the
fact that edge to face interaction detected here for both
simple compounds I and II was also found to be an
important factor of structure organization in natural
biologically active substances like CLA [6].
N-.p-Dimethylaminophenyl)-a-.3-acetamido-4-
nitrophenyl) nitrone .Scheme 1) was prepared by us
for further synthesis of 3-acetamido-4-nitrobenzalde-
hyde. Copper.II) nitrate in acetic anhydride [7] was
chosen for the nitration of m-toluidine because of its
ability to introduce the nitro group into the ortho posi-
tion towards acetamide group .see Scheme 3). As it
was mentioned in Ref. [7] the major product of nitra-
tion is 3-acetamido-4-nitrotoluidine. Additionally,
another mononitro isomer .6-nitro) was obtained in
Scheme 2.

G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
243
Scheme 3.
[8] has mp 84.9±85.58C). After addition of concen-
trated solution of ammonia into washing of 3-amino-
4-nitrotoluidine another nitro isomer .6-nitro) was
obtained.
1H-NMR data for 3-acetamido-4-nitrotoluidyne
.500 MHz, CDCl3) s: 10.5 .s, H1), 8.7 .s, H2), 8.2
.d, J ˆ 8.75 Hz, H5), 7.2 .d, J ˆ 4.5 Hz, H6), 2.45 .s,
CH3), 2.3 .s, CH3).
crude product 3-acetamido-4-nitrobromotoluidyne
was crystallized from ethyl alcohol. To the crude
product an absolute ethanol .53.76 cm3) was added
and 110 mmol of pyridine were dropped. The solution
was heated at the re¯ux temperature for 45 min and
immediately transferred to a wide-neck Erlenmeyer
¯ask. After cooling the mixture, crude crystals of 3-
acetamido-4-nitrobenzylpyridinium bromide were
collected and recrystallized from ethyl alcohol
.10.94 g, mp 236.5±237.58C). Needle-like, yellow
crystals of II were obtained by slow evaporation
from a solution which contains a mixture of methanol
and ethyl acetate.
1H-NMR data for 3-acetamido-4-nitrobenzylpyri-
dynium bromide .500 MHz, DMSO, TMS int. ref.
s: 0.00) s: 10.47 .s, H1), 9.27 .m, J ˆ 6.86 Hz,
H10, H14), 8.74 .m, J ˆ 8.0 Hz, H12), 8.24 .m,
H11, H13), 8.00 .d, J ˆ 8.94 Hz, H5), 7.67 .s, H2),
7.50 .d, J ˆ 8.64 Hz, H6), 6.93 .s, H2), 6.65 .d,
2.1.2. 3-Acetamido-4-nitrobenzylpyridinium bromide
The 3-acetamido-4-nitrotoluidyne .30 mmol) [9]
was dissolved in carbon tetrachloride .170 cm3) and
next solid potassium carbonate .61.8 mmol) was
added into the solution. To the above mixture
37.5 mmol of bromine in carbon tetrachloride
.45 cm3) was added dropwise and everything was
boiled and irradiated with 250 W tungsten lamp.
After the bromine addition was completed the solu-
tion was re¯uxed and irradiated for next 5 h. The

244
G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
Table 1
Crystal data for N-.p-dimethylaminophenyl)-a-.3-acetamido-4-nitrophenyl)nitrone .I) and 3-acetamido-4-nitrobenzylpyridinium bromide .II)
I
II
Empirical formula
Temperature .K)
Formula weight
Colour
C17H18N4O4
299.1)
.C14H14N3O3)1Br2
120.1)
342.35
352.19
Brown
Yellow
Wavelength .l)
Crystal system
Space group
0.71073
0.71073
Triclinic
Monoclinic
C2/c
P1
Unit cell dimensions:
Ê
a .A)
6.813.4)
24.87.2) [25.20.2)]a
b .A)
8.646.5)
14.644.6)
6.919.5) [6.971.6)]a
Ê
20.034.15) [20.157.15)]a
Ê
c .A)
a .80
b .8)
g .8)
75.45.4)
78.56.4)
124.28.7) [124.14.9)]a
89.10.4)
Ê 3
Volume .A )
817.8.8)
2849.4)
Z
2
1.390
8
Density .calculated) .g cm23
)
1.642 [1.569]a
Density .measured) .g cm23
Absorption coef®cient .mm21
F.000)
)
1.372
1.548
)
0.10
2.90
360
1424
Crystal size .mm)
Index ranges
0.2 £ 0.5 £ 0.5
29 ! h ! 8
211 ! k ! 8
219 ! l ! 18
5628
0.1 £ 0.2 £ 0.05
230 ! h ! 26
0 ! k ! 8
0 ! l ! 25
Re¯ections collected
Independent re¯ections
Re®nement method
Data/parameters
5038
3614 ꢀRꢀint† ˆ 0:0218†
Full-matrix least-squares on F2
3614/298
2849 ꢀRꢀint† ˆ 0:0879†
2849/232
1.043
Goodness-of-®t on F2
1.089
Final R indices .I . 2s.I))
R1 ˆ 0:0773
wR2 ˆ 0:1795
R1 ˆ 0:127
wR2 ˆ 0:222
0.0555
0.0819
0.157
R indices .all data)
0.101
a
The values given in square brackets are for 291 K.
J ˆ 8.94 Hz, H6), 6.05 .s, H71, H7), 5.91 .s, H71,
H72), 2.07 .s, CH3).
methylaniline hydrochloride .15 mmol) and ethanol
.47.9 cm3) were placed in a three-necked ¯ask equipped
with an ef®cient stirrer, thermometer, and a dropping
funnel, and immersed in an ice-salt bath. To the stirred
solution 40 mmol of sodium hydroxide in water
.15 cm3) was added at 0±58C. The stirring was
continued over a period of 1 h. At the end of this time
ice-cold water .15 cm3) was added and N-.p-dimethy-
lophenyl)-a-.3-acetamido-4-nitrophenyl)nitrone crys-
1H-NMR data .500 MHz, D2O, dioxan int. ref. s:
3.68) s: 8.88 .m, 3J ˆ 19.5 Hz, 4J ˆ 4.5 Hz, H10,
H14), 8.55 .m, H12), 8.06 .m, H11, H13 and H5),
7.96 .d, 3J ˆ 8.80 Hz, H5) 7.81 .s, H2), 7.34 .d,
3J ˆ 8.62 Hz, H6), 6.90 .s, H2), 6.55 .d,
3J ˆ 8.44 Hz, H6), 5.88 .s, H71, H72), 5.70 .s, H71,
H72), 2.15 .s, CH3).
Í
tals were collected on a Buchner funnel. The crystals
were washed with cold water. The crude product was
then recrystallized from acetone .2.57 g, mp 192±
1938C). Platy shapes, dark brown crystals of I were
obtained by slow evaporation from acetone.
2.1.3. N-3p-dimethylophenyl)-a-33-acetamido-4-
nitrophenyl)nitrone
The wet 3-acetamido-4-nitrobenzylpyridinium
bromide .15 mmol) [9], together with of p-nitrosodi-

G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
245
Table 2
Positional coordinates and equivalent thermal parameters .with e.s.d.'s in parentheses)
x
y
z
Uequiv/Uiso
I
C1
0.3110.4)
0.3655.4)
0.2476.4)
0.0683.4)
0.0149.5)
0.1318.5)
0.4471.4)
0.4529.4)
0.4703.6)
0.7401.5)
0.8720.5)
0.8376.4)
0.6637.4)
0.5328.4)
0.5671.4)
1.1505.6)
0.9350.6)
0.3027.4)
0.5280.3)
0.4574.3)
0.3394.3)
0.2891.3)
0.3567.4)
0.4753.4)
0.6507.3)
0.3213.3)
0.2214.5)
0.9003.4)
1.0174.4)
1.1003.3)
1.0557.3)
0.9375.3)
0.8591.3)
1.2558.6)
1.2986.4)
0.2729.3)
0.1641.3)
0.7361.3)
1.2192.3)
0.0991.3)
0.1237.3)
0.4356.3)
0.7190.3)
0.193.4)
0.498.3)
0.315.4)
0.519.3)
0.681.3)
0.855.4)
1.049.4)
1.106.3)
0.909.3)
0.147.5)
0.290.5)
0.174.5)
0.1314.2)
0.2197.2)
0.2904.2)
0.2692.2)
0.1818.2)
0.1133.2)
0.0649.2)
0.4161.2)
0.5137.2)
0.0561.6)
0.0531.7)
0.0488.6)
0.0504.6)
0.0636.8)
0.0646.8)
0.0550.7)
0.0600.6)
0.0691.9)
0.0765.10)
0.0758.10)
0.0542.7)
0.0568.7)
0.0557.7)
0.0543.7)
0.0808.11)
0.0710.9)
0.0561.6)
0.0603.6)
0.0579.6)
0.0665.7)
0.0899.8)
0.0856.8)
0.0980.9)
0.1067.10)
0.077.10)
0.064.8)
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
N1
20.0535.2)
20.1144.2)
20.2043.2)
20.2301.2)
20.1693.2)
20.0796.2)
20.2377.4)
20.3590.3)
0.3793.2)
0.3351.2)
20.0191.2)
20.2638.2)
0.4149.2)
0.3106.2)
0.3751.2)
20.0529.2)
0.415.2)
N2
20.0662.4)
0.4226.3)
0.9675.4)
20.0317.4)
20.2148.3)
0.5645.4)
0.2669.4)
0.223.5)
0.502.5)
20.104.5)
0.089.4)
0.568.4)
0.775.5)
1.001.5)
0.629.4)
0.418.4)
0.368.6)
0.488.6)
0.602.7)
1.131.6)
1.224.6)
1.230.6)
1.037.5)
0.801.6)
0.940.6)
N3
N4
O1
O2
O3
O4
H1
H2
0.228.2)
H5
0.168.2)
0.070.8)
H6
0.048.2)
0.073.9)
H7
0.084.2)
0.004.3)
0.066.8)
H10
H11
H13
H14
H91
H92
H93
H161
H162
H163
H171
H172
H173
0.090.10)
0.094.10)
0.052.7)
20.093.3)
20.292.2)
20.187.2)
0.541.3)
0.065.8)
0.096.12)
0.110.13)
0.125.15)
0.096.13)
0.114.13)
0.120.16)
0.085.10)
0.099.12)
0.104.13)
0.551.3)
0.510.3)
1.274.4)
1.343.5)
1.170.5)
1.385.4)
1.352.4)
1.224.5)
20.176.3)
20.281.3)
20.234.3)
20.385.2)
20.354.3)
20.396.3)
II
Br
C1
C2
C3
C4
C5
C6
0.38374.3)
0.3170.2)
0.3155.2)
0.2568.2)
0.1988.2)
0.2000.2)
0.2580.2)
0.53383.8)
0.0490.8)
0.0519.8)
0.0635.7)
0.0710.7)
0.0669.7)
0.0559.8)
0.12557.3)
0.1782.3)
0.2461.3)
0.2408.3)
0.1624.3)
0.0936.3)
0.1003.3)
0.02208.16)
0.0155.10)
0.0172.11)
0.0126.11)
0.0164.12)
0.0165.11)
0.0179.11)

246
G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
Table 2 .continued)
x
y
z
Uequiv/Uiso
C7
0.3793.2)
0.0354.10)
0.0986.7)
0.0733.9)
0.1825.3)
0.3895.3)
0.4530.3)
0.3101.4)
0.3908.4)
0.4292.4)
0.3848.4)
0.3041.4)
0.3110.2)
0.1482.3)
0.2675.2)
0.2051.2)
0.0797.2)
0.4066.2)
0.300.3)
0.295.3)
0.040.3)
0.055.3)
0.278.4)
0.413.4)
0.488.4)
0.416.3)
0.270.3)
0.158.4)
0.160.4)
0.440.3)
0.482.4)
0.485.3)
0.0193.10)
0.0167.12)
0.0197.13)
0.0259.15)
0.0256.16)
0.0229.14)
0.0237.14)
0.0157.12)
0.0156.10)
0.0187.10)
0.0156.9)
0.0251.9)
0.0339.11)
0.0249.9)
0.019
C8
C9
0.3101.2)
0.2962.3)
0.4652.3)
0.5122.3)
0.5301.3)
0.5016.3)
0.4563.3)
0.2571.2)
0.1346.2)
0.4372.2)
0.1291.2)
0.0872.2)
0.3641.2)
0.217.2)
0.351.2)
0.156.2)
0.260.2)
0.447.3)
0.523.3)
0.560.3)
0.517.3)
0.438.3)
0.383.3)
0.383.3)
0.253.3)
0.314.3)
0.319.2)
C10
C11
C12
C13
C14
N1
20.1182.10)
20.1082.10)
0.0680.9)
0.2369.9)
0.2207.8)
0.0655.6)
0.0800.6)
0.0449.7)
0.0526.6)
0.1140.6)
0.1402.6)
0.047.8)
N2
N7
O1
O2
O3
H1
H2
0.034.8)
0.021
H5
H6
0.065.7)
0.052.8)
0.020
0.021
H10
H11
H12
H13
H14
H71
H72
H91
H92
H93
20.204.10)
20.206.9)
0.069.8)
0.031
0.031
0.027
0.028
0.383.8)
0.322.8)
0.019
0.138.9)
20.100.9)
0.088.8)
0.023
0.023
0.024
0.171.9)
0.024
20.064.8)
0.024
1H-NMR data for N-.p-dimethylophenyl)-a-.3-
acetamido-4-nitrophenyl)nitrone .500 MHz, DMSO,
TMS int. ref.) s: 10.43 .s H7), 8.86 .s, H5), 8.59 .s,
H1), 8.27 .s, H6), 8.16 .d, J ˆ 8.5 Hz, H14), 8.03 .d,
J ˆ 8.5 Hz, H13), 7.82 .d, J ˆ 7.2 Hz, H10), 7.35 .s,
H2), 6.79 .d, J ˆ 7.2 Hz, H11), 3.00 .s, H17, H16),
2.08 .s, H9).
using shelxl [11]. For II the analytical corrections
for absorption were applied; Tmin and Tmax 0.695 and
0.877, respectively. All positions of the H atoms were
found from different Fourier maps and re®ned with
Uiso equal to 1.2 Uequiv of the parent atoms. Final
atom parameters with their estimated standard devia-
tions are listed in Table 2. The density of II was
measured by ¯otation in the mixture of CCl4/CHCl3.
2.2. X-ray diffraction
Diffraction data for crystal I were collected on a
Kuma KM4CCD area detector diffractometer .v
scan) and for II on a Kuma KM4 k-geometry diffract-
ometer .v±2u scan), with graphite-monochromatized
MoKa radiation. Since crystal of I show phase transi-
tion below 210 K the data collection for this crystal
was at room temperature. The experimental details are
given in Table 1. Both structures were solved by direct
methods using the shelxs program [10] and re®ned
3. Results and discussion
3.1. Analysis of crystallographical data
The molecular structure and numbering scheme of
the N-.p-dimethylaminobenzyl)-a-.3-acetamido-4-
nitrophenyl)nitrone, I is shown in Fig. 1.
The molecule I has two aromatic rings attached to
nitrone moiety. There are two different substituents

G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
247
Fig. 1. The structure of the N-.p-dimethylaminobenzyl)-a-.4-nitro-3-acetaminotoluene)nitrone showing 50% probability displacement ellip-
soids and atom-numbering scheme. Dashed lines indicate intramolecular hydrogen bonds.
connected to the benzene skeleton in the ®rst ring:
acetamido and nitro. The second ring is substituted
by N,N-dimethylamine group. Both aromatic rings
are coplanar .dihedral angle between the mean
aromatic planes is 0.788).
The crystal structure of II consists of 3-acetamido-
4-nitrobenzylpyridinium cations and the Br2 anions.
A plot of the cation is depicted in Fig. 2. In the cation
the C8±O3 bond lengths are 1.208.3) and
Ê
1.221.6) A for I and II, respectively. The bond
lengths and angles are given in Table 3. These differ-
ences are, probably, due to the intramolecular
hydrogen bond between the aromatic H2 atom and
the O3 atom of the carboxyl group [3]. Weak
hydrogen bond existing between the amide H1 and
the nitro O1 atoms explains the coplanarity of the
acetamide and nitro group as it was observed for 4-
nitro compounds [1]. The angle between the nitro
group and the aromatic ring is 8.1.3)8 and 11.06.1)8
for I and II, respectively. This planar conformation is
also stabilized by the intramolecular contact between
the nitro O2 atom and the H5 atom of the aromatic
ring. The intra- and intermolecular hydrogen bonds
are presented in Table 4.
the
3-acetamido-4-nitrobenzyl
substituent
is
connected with pyridine ring. The pyridine ring is
situated perpendicular to the benzene ring .dihedral
angle between respective mean planes is 838).
In both the structures the acetamide group is almost
coplanar with the plane of the aromatic ring. The most
Ê
displaced atoms from the plane are O3 .0.407.6) A for
Ê
I and 0.617.10) A for II) and C8 .0.212.5) A for I and
Ê
Ê
0.262.10) A for II).
The most signi®cant difference in the geometrical
parameters is observed for the acetamide group and
Ê
C1±C2 bond length .1.403.4) and 1.383.7) A for I
and II, respectively). The C8±N1 bond lengths are
Ê
1.364.3) and 1.389.7) A for I and II, respectively;
In I the O4 atom of the nitrone moiety makes
hydrogen bonds with the H6 and the H14 atoms of
the aromatic rings .see Table 4). It explains the elon-
gating of the O4±N3 bond length, which has a partial
Ê
double bond character .1.281.3) A). However, this
distance is shorter than it was observed in the other

248
G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
Fig. 2. The structure of 3-acetamido-4-nitrobenzylpyridinium cation showing 50% probability displacement ellipsoids and atom-numbering
scheme. Dashed lines indicate intramolecular hydrogen bonds.
nitrones [12±14]. Here the conjugation is observed in
the Ar±CyN ! O region with N±O bond length shor-
tened in relation to the unconjugated nitrones [12].
The 3-acetamido-4-nitrobenzene substituent in the
cation of the structure II is situated perpendicular to
the pyridine ring. The C6±C1±C7±N7 and C1±C7±
N7±C10 torsion angles are 175.6.5) and 93.7.6)8,
respectively. The selected torsion angles for crystal
II is given in Table 5. Intramolecular face-to-edge
conformation is stabilized by the C2±H2´´´N7
hydrogen bond .see Table 4). The geometry of the
symmetry are linked by the weak intermolecular C±
H´´´O hydrogen bonds .see Table 4), forming in®nite
chains along a .Fig. 3). These chains are related by the
center of symmetry to make stacking along b; the
Ê
distance formed is about 3.5 A. The short intermole-
cular contacts are observed between the symmetry-
related O1 atoms of the nitro group. The O1´´´O1
Ê
.x, 2y, 1 2 z) distance is 2.755.4) A. Similar
distances were observed previously in the other nitro
compounds [18].
In the crystal II each Br2 anion is linked with ®ve H
Ê
atoms with H´´´Br , 2.95 A .see Table 4). The 3-
acetamido-4-nitrobenzene substituents of the mole-
cules are related by the two-fold axis form columns
3-acetamido-4-nitrobenzylpirydynium
similar to the other salts of pyridinium [15±17].
In the crystal I, molecules related by the center of
cation
is

G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
Table 3 .continued)
249
Table 3
Bond lengths .A) and bond angles .8) .with e.s.d.'s in parentheses)
for I and II
Ê
I
II
I
II
C14±C13±C12
C13±C14±C15
C13±C14±N7
C14±C15±C10
C14±C15±N3
C10±C15±N3
C8±N1±C3
121.6.3)
121.1.3)
±
118.2.6)
±
121.3.5)
C1±C2
1.403.4)
1.406.4)
1.445.4)
1.387.4)
1.418.4)
1.405.3)
1.384.4)
1.448.3)
1.373.4)
1.307.3)
±
1.383.7)
1.418.7)
1.507.7)
1.405.6)
1.414.7)
1.400.6)
1.396.7)
1.457.6)
1.374.7)
±
C1±C6
118.1.3)
118.1.2)
123.8.2)
128.8.2)
120.3.2)
119.3.2)
120.5.2)
122.2.2)
115.3.2)
122.4.2)
120.6.3)
120.7.3)
118.3.3)
±
±
C1±C7
±
C2±C3
C3±C4
±
127.2.4)
C3±N1
C4±C5
O2±N2±O1
121.8.4)
O2±N2±C4
118.9.4)
C4±N2
C5±C6
O1±N2±C4
O4±N3±C7
119.3.4)
±
C7±N3
C7±N7
C8±C9
O4±N3±C15
C7±N3±C15
C12±N4±C16
C12±N4±C17
C16±N4±C17
C10±N7±C7
C10±N7±C14
C14±N7±C7
±
1.489.7)
1.505.7)
1.389.7)
1.221.6)
1.362.10)
±
±
1.499.4)
1.364.3)
1.208.3)
1.372.4)
1.387.4)
±
±
C8±N1
C8±O3
C10±C11
C10±C15
C10±N7
C11±C12
C12±C13
C12±N4
C13±C14
C14±C15
C15±N3
C16±N4
C17±N4
O1±N2
O2±N2
O4±N3
±
±
120.6.5)
120.6.4)
118.3.5)
±
1.347.8)
1.374.9)
1.396.8)
±
±
1.395.4)
1.400.4)
1.369.3)
1.374.4)
1.381.4)
1.448.3)
1.436.4)
1.449.4)
1.229.3)
1.222.3)
1.281.3)
along b. The 4-nitro-3-acetamidobenzene substituents
of the molecules related-symmetry of the former
columns are nearly parallel to the ac plane with inter-
1.357.9)
±
±
±
Ê
planar distances about 3.5 A. The crystal packing can
±
be described as being composed of the three-dimen-
sional network via C±H´´´O intermolecular hydrogen
bonds and interactions between the aromatic rings of
the adjacent molecules .Fig. 4.).
1.235.5)
1.227.6)
±
C2±C1±C6
C2±C1±C7
C6±C1±C7
C1±C2±C3
N1±C3±C2
N1±C3±C4
C2±C3±C4
C5±C4±C3
C5±C4±N2
C3±C4±N2
C6±C5±C4
C5±C6±C1
N3±C7±C1
N7±C7±C1
O3±C8±N1
O3±C8±C9
N1 ±C8 ±C9
N7 ±C10±C11
C11±C10±C15
C10±C11±C12
C11±C12±C13
N4±C12±C11
N4±C12±C13
118.8.2)
116.5.2)
124.7.2)
122.5.3)
121.6.2)
121.4.2)
117.0.2)
120.8.2)
116.2.2)
123.0.2)
121.4.3)
119.5.3)
126.8.3)
±
119.9.4)
122.9.4)
117.3.4)
122.0.5)
120.4.4)
122.7.4)
116.9.4)
121.4.4)
116.0.4)
122.6.4)
120.7.5)
119.2.4)
±
3.2. NMR measurements and spectra analysis
NMR spectra were recorded on BruÈker spectro-
meter operated on 500 MHz in DMSO solution with
TMS as internal reference. Concentration of sample
were 8 and 10 mg ml21 for compounds I and II,
respectively.
Changes in spectra going from II to I support the
way of synthesis used. Assignments of the protons in
molecules to signal in spectra were made based on the
experiments carried out: COSY, C±H correlation,
inverse C±H correlation, and for II from H±D
exchange going from DMSO to D2O solution.
For the compound II duplicate number of signals
for the 3-acetamido-4-nitrobenzyl substituent is
observed in the standard COSY spectrum similar to
the 1H-NMR spectrum .see Fig. 5). As it was
expressed in NMR data for II signal for proton H2
111.4.4)
123.2.4)
122.2.5)
114.6.4)
120.0.6)
±
123.9.3)
121.4.3)
114.7.3)
±
121.0.3)
121.7.3)
116.6.2)
121.4.3)
122.0.2)
120.0.6)
119.8.5)
±
±

250
G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
Table 4
Probable hydrogen bonds intra- and intermolecular for crystals I and II
Ê
D±H .A)
Ê
H¼A .A)
Ê
D¼A .A)
D±H´´´A
D±H¼A .8)
I
N1±H1´´´O1
C2±H2´´´O3
C5±H5´´´O2
C5±H5´´´O4a
C6±H6´´´O4
C14±H14´´´O4
C14±H14´´´O2a
C16±H162´´´O3b
II
0.88.3)
1.04.3)
0.96.3)
0.96.3)
1.03.3)
0.93.3)
0.93.3)
0.93.4)
1.93.3)
2.21.3)
2.31.3)
2.28.3)
2.17.3)
2.29.3)
2.55.3)
2.37.5)
2.639.3)
2.838.4)
2.662.4)
3.127.4)
2.794.4)
2.649.4)
3.409.4)
3.295.5)
137.3)
117.2)
101.2)
147.2)
117.2)
102.2)
154.2)
173.3)
N1±H1´´´O1
C2±H2´´´O3
C2±H2´´´N7
C5±H5´´´Brc
C5±H5´´´O2
C7±H71´´´Br
C7±H72´´´Brd
C9±H91´´´Bre
C12±H12´´´O3f
C14±H14´´´Br
C14±H14´´´O1g
0.90.5)
0.89.5)
0.89.5)
1.02.5)
1.02.5)
0.89.6)
1.06.6)
0.97.5)
0.98.6)
0.91.6)
0.91.6)
1.92.5)
2.19.5)
2.50.5)
2.96.5)
2.27.5)
2.82.6)
2.63.6)
2.89.5)
2.37.6)
2.82.6)
2.54.5)
2.652.6)
2.790.7)
2.811.6)
3.716.6)
2.678.6)
3.653.7)
3.674.7)
3.641.9)
3.173.8)
3.671.6)
3.063.7)
137.4)
124.4)
101.3)
132.3)
102.3)
156.5)
168.4)
164.4)
139.5)
157.4)
117.4)
a
Symmetry codes: 2x, 1 2 y, 2z.
2 2 x, 2 2 y, 2z.
b
c
d
e
f
0.5 2 x, 0.5 2 y, 2z.
x, y 2 1, z.
0.5 2 x, y 2 0.5, 0.5 2 z.
1 2 x, 2y, 1 2 z.
0.5 2 x, 0.5 1 y, 0.5 2 z.
g
appear in two positions of spectrum dH2c ˆ
6:93 ppm and dH2s ˆ 7:67 ppm; where designation
c is valid for crystal like structure and s means posi-
tion of proton appeared in structure found only in
solution. The difference between these two positions
represents change the orientation of edge the 3-acet-
amido-4-nitrobenzyl substituent against face pyridine
ring. This effect is accompanied by similar situation
observed for the pair of coupled protons H5 and H6
giving two AB systems. Like for H2, we can write an
equation for proton H6
dH2c 2 dH2s ˆ 20:74 ppm
dH6c 2 dH6s ˆ 0:79 ppm
The distinct difference in chemical shifts H2 and
H6 for two conformations of II derived from two edge
to face structures where one is similar to this observed
in crystal state and second is with bond ±H6C6±
C5H5± almost coaxially oriented toward high-®eld
shielding plane of pyridine ring. It must be marked
here that similar absolute values of above differences
evidences existence only two edge to face forms in
solution .see Fig. 6) and there is no other form visible
in equilibrium. It is surprising, that edge to face inter-
action in II is strong enough to form two different
Table 5
Selected torsion angles .8) .with e.s.d's in parentheses) for crystal II
C6±C1±C7±N7
O3±C8±N1±C3
C9±C8±N1±C3
C2±C3±N1±C8
C4±C3±N1±C8
C11±C10±N7±C7
C13±C14±N7±C7
C1±C7±N7±C10
C1±C7±N7±C14
175.6.5)
3.6.8)
2 174.7.5)
15.0.8)
2 165.6.5)
2 170.8.5)
169.1.5)
93.7.6)
2 78.5.6)

Fig. 3. View of the crystal packing of the compound I with dashed lines indicating the intermolecular hydrogen bonds.

252
G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
Fig. 4. View of the crystal packing of the compound II with dashed lines indicating the intermolecular hydrogen bonds .symmetry codes: .i)
0.5 2 x, 0.5 2 y, 2z; .ii) x, y 2 1, z; .iv) 0.5 2 x, 20.5 1 y, 0.5 2 z; .v) 1 2 x, 2y, 1 2 z; .vi) 0.5 2
x, 0.5 1 y, 0.5 2 z).

G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
253
1
Fig. 5. H-NMR spectrum .aromatic region) for compound II in D2O. Designations c and s indicate that signals derived from crystal like and
solution appeared structures respectively .both of them are in equilibrium in solution). The H5c dublet is overlapped by H11 and H13 multiplet.
Fig. 6. Two structures in solution of compound II; designation: c Ð structure in solution same like in crystal, s Ð structure appeared in
solution only.

254
G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
1
Fig. 7. H-NMR spectrum .aromatic region) for compound I. Strongly predominate AB system from two pairs protons .H14, H13) and .H10,
H11) giving dublets at 6.85 and at 7.80 ppm as well as double less intensity AB system for H5, H6 pair evidenced the structure with
perpendicularly oriented parts of molecule .see text). Low intensity signals appeared in spectrum were excluded from consideration. The
signal for H7 at 8.85 ppm represents protonated on nitrone oxygen form of molecule while signal at 8.25 ppm derived from this same
unprotonated group. There is no in¯uence visible for this process on longer distance distributed protons.
structures only in solution .DMSO, D2O) where are no
limits for conformational changes contrary to situa-
tion in the crystal net. The picture presented is also
consistent with the the fact of appearance in the spec-
trum only one set of signals for pyridine ring. Its
perpendicular orientation against second ring in both
structures does not differ chemical shifts and only one
spin system characteristic for pyridine moiety is
observed.
For I crystallographical data have shown almost
planar structure. For such a structure in solution we
should expect for the N,N-dimethylaniline substituent
on the nitrone bond two AB systems in COSY spectra.
In opposition to this only one distinct AB system is
observed for two pairs of protons H10, H11 and H14,
H13 .see Fig. 7). The equivalence of these two pairs
protons is possible only in the case of perpendicular
orientation of this aromatic substituent to the plane

Fig. 8. The structure change of compound I due to transfer from crystal state c to solution s. Designations: c Ð structure in crystal, s Ð structure appeared in solution only.

256
G. Rusek et al. / Journal of Molecular Structure 597 32001) 241±257
containing the rest of the molecule .see Fig. 8).
Conclusion is that in this case `transfer' of the mole-
cule from crystal state to the solution gives possibility
to form open edge to face like structure. The role of
face in this structure plays the N,N-dimethylaniline
substituent while the nitrone bond appears here as
edge .the angle between face and edge is close to
1208 so we called it open edge to face structure). All
this gave us an argument to state that for nitrones like
compound I in solution the tendency for edge to face
structure creation predominates the electron pair in
nitrone bond coupling with aromatic substituents,
which needs the planar structure of whole molecule
like the one found in crystal net. The last statement is
consistent with negative results of trials to obtain
liquid crystal nitrones where two aromatic substitu-
ents are settled on this moiety. In respect to the need
of coplanar orientation of aromatic parts in molecules
possessing liquid crystal phases our observation
presented in this paper explains why aromatic nitrones
do not reveal such properties. Using the comparison of
nitrones to amides presented in introductory part of
this work, we can predict that also an amide bond is
not a good candidate for construction of liquid crystals
because of charged resonance form of this bond
presence what might destroy coplanar orientation of
aromatic rings in liquid state. An examination of
liquid crystals database for aromatically substituted
nitrones and amides fully support our conclusions
[19]. None of the nitrones and amides present
possessed liquid crystals properties.
acetamido-4-nitrobenzylpyridynium bromide appears
in edge to face conformation in crystal state as well as
in solution. There in solution only two possible edge
to face structures of this compound were detected.
For N-.p-dimethylaminophenyl)-a-.3acetamido-4-
nitrophenyl) nitrone the planar structure of whole
molecule was established by crystallographical
method.
The NMR measurements have given proofs that
main conformation of this compound in solution has
perpendicularly oriented N,N-dimethylaniline substi-
tuent against the rest of the molecule.
This tendency has been recognized as the main
cause of impossibility .known from literature) to
obtain aromatically substituted nitrones possessed
liquid crystal phases.
Above results are giving an argument to state that
edge to face interaction between aromatic rings is
very important and common factor of the structure
formation in small molecules like the ones presented
here as well as in the larger peptides that was
discussed in the article.
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The data presented above is an evidence that 3-

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