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Single crystals of methyl-
p-aminobenzoate (MAB), C
8H
9NO
2, were obtained during the synthesis of 4-amino-
N'-(5-nitro-2-thienylmethylene)benzohydrazide. A
P2
1/
c polymorph [
a = 8.5969 (4) Å,
b = 5.6053 (2) Å,
c = 15.5397 (7) Å and
= 96.172 (2)°] of MAB was found and the intra- and intermolecular geometries were compared with those of the previously known
C2/
c structure [
a = 16.242 (2) Å,
b = 8.113 (2) Å,
c = 12.724 (2) Å and
= 69.17 (1)°; Xianti (1983).
Jiegou Huaxue,
2, 219-221].
Supporting information
CCDC reference: 231080
MAB was obtained from benzoic acid (30 mmol) under reflux with methanol (60 mmol) and concentrated sulfuric acid (0.06 ml) for 4 h. The reaction pH was then adjusted to around 7 with a solution of 10% NaOH. The resulting yellow crystals were filtered, washed with small amounts of cold water, and dried under reduced pressure and phosphorus pentoxide.
H atoms of the phenyl and methyl groups were positioned stereochemically and were refined with fixed individual displacement parameters [Uiso(H) = 1.2Ueq(C) or 1.5Ueq(Cmethoxy)] using a riding model, with aromatic C—H distances of 0.95 Å and methyl C—H distances of 0.98 Å. The two amine H atoms were located by difference Fourier synthesis and were set as isotropic.
Data collection: Collect (Nonius, 1998); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).
methyl-
p-aminobenzoate
top
Crystal data top
C8H9NO2 | F(000) = 320 |
Mr = 151.16 | Dx = 1.349 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 13722 reflections |
a = 8.5969 (4) Å | θ = 3.4–27.5° |
b = 5.6053 (2) Å | µ = 0.10 mm−1 |
c = 15.5397 (7) Å | T = 120 K |
β = 96.172 (2)° | Needle, yellow |
V = 744.49 (6) Å3 | 0.17 × 0.06 × 0.02 mm |
Z = 4 | |
Data collection top
Nonius KappaCCD diffractometer | 1040 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.070 |
Horizonally mounted graphite crystal monochromator | θmax = 25°, θmin = 3.7° |
Detector resolution: 9 pixels mm-1 | h = −10→10 |
ϕ scans and ω scans with κ offsets | k = −6→6 |
15706 measured reflections | l = −18→18 |
1313 independent reflections | |
Refinement top
Refinement on F2 | 0 restraints |
Least-squares matrix: full | H atoms treated by a mixture of independent and constrained refinement |
R[F2 > 2σ(F2)] = 0.040 | w = 1/[σ2(Fo2) + (0.0631P)2 + 0.0853P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.104 | (Δ/σ)max < 0.001 |
S = 1.05 | Δρmax = 0.17 e Å−3 |
1313 reflections | Δρmin = −0.26 e Å−3 |
108 parameters | |
Crystal data top
C8H9NO2 | V = 744.49 (6) Å3 |
Mr = 151.16 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 8.5969 (4) Å | µ = 0.10 mm−1 |
b = 5.6053 (2) Å | T = 120 K |
c = 15.5397 (7) Å | 0.17 × 0.06 × 0.02 mm |
β = 96.172 (2)° | |
Data collection top
Nonius KappaCCD diffractometer | 1040 reflections with I > 2σ(I) |
15706 measured reflections | Rint = 0.070 |
1313 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.040 | 0 restraints |
wR(F2) = 0.104 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.05 | Δρmax = 0.17 e Å−3 |
1313 reflections | Δρmin = −0.26 e Å−3 |
108 parameters | |
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
C1 | 0.80614 (17) | 0.3526 (3) | 0.17141 (9) | 0.0281 (4) | |
C2 | 0.67864 (17) | 0.2148 (3) | 0.19080 (9) | 0.0286 (4) | |
H2 | 0.6962 | 0.0692 | 0.2216 | 0.034* | |
C3 | 0.52753 (17) | 0.2893 (3) | 0.16547 (9) | 0.0292 (4) | |
H3 | 0.4421 | 0.1937 | 0.1788 | 0.035* | |
C4 | 0.49877 (16) | 0.5026 (2) | 0.12064 (9) | 0.0271 (4) | |
C5 | 0.62569 (17) | 0.6391 (3) | 0.10085 (9) | 0.0288 (4) | |
H5 | 0.6077 | 0.7844 | 0.0699 | 0.035* | |
C6 | 0.77676 (17) | 0.5658 (3) | 0.12551 (9) | 0.0299 (4) | |
H6 | 0.8619 | 0.6608 | 0.1113 | 0.036* | |
C7 | 0.33586 (17) | 0.5786 (3) | 0.09731 (9) | 0.0283 (4) | |
C8 | 0.16864 (18) | 0.8875 (3) | 0.04241 (11) | 0.0386 (4) | |
H8A | 0.1727 | 1.0473 | 0.0172 | 0.058* | |
H8B | 0.1172 | 0.8957 | 0.0956 | 0.058* | |
H8C | 0.1095 | 0.7808 | 0.001 | 0.058* | |
N1 | 0.95806 (15) | 0.2844 (3) | 0.19940 (9) | 0.0326 (4) | |
O1 | 0.22084 (12) | 0.46162 (19) | 0.10881 (7) | 0.0352 (3) | |
O2 | 0.32538 (11) | 0.79740 (18) | 0.06218 (7) | 0.0338 (3) | |
H11 | 1.032 (2) | 0.342 (3) | 0.1705 (11) | 0.038 (5)* | |
H12 | 0.970 (2) | 0.131 (4) | 0.2187 (11) | 0.048 (5)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C1 | 0.0277 (8) | 0.0310 (8) | 0.0254 (7) | −0.0001 (6) | 0.0021 (6) | −0.0032 (6) |
C2 | 0.0318 (8) | 0.0264 (8) | 0.0276 (8) | −0.0005 (6) | 0.0031 (6) | 0.0004 (6) |
C3 | 0.0291 (8) | 0.0301 (8) | 0.0290 (8) | −0.0049 (6) | 0.0057 (6) | −0.0012 (6) |
C4 | 0.0264 (8) | 0.0297 (8) | 0.0253 (7) | −0.0018 (6) | 0.0034 (6) | −0.0027 (6) |
C5 | 0.0311 (8) | 0.0276 (8) | 0.0279 (8) | −0.0013 (6) | 0.0034 (6) | −0.0001 (6) |
C6 | 0.0258 (8) | 0.0308 (8) | 0.0333 (8) | −0.0048 (6) | 0.0042 (6) | 0.0004 (6) |
C7 | 0.0302 (8) | 0.0296 (8) | 0.0257 (7) | −0.0021 (6) | 0.0054 (6) | −0.0029 (6) |
C8 | 0.0268 (9) | 0.0389 (9) | 0.0498 (10) | 0.0059 (7) | 0.0030 (7) | 0.0031 (8) |
N1 | 0.0258 (7) | 0.0350 (8) | 0.0373 (8) | 0.0013 (6) | 0.0044 (6) | 0.0055 (6) |
O1 | 0.0266 (6) | 0.0400 (7) | 0.0396 (6) | −0.0038 (5) | 0.0056 (5) | 0.0017 (5) |
O2 | 0.0250 (6) | 0.0335 (6) | 0.0427 (6) | 0.0025 (4) | 0.0023 (5) | 0.0030 (5) |
Geometric parameters (Å, º) top
C1—N1 | 1.385 (2) | C5—H5 | 0.95 |
C1—C2 | 1.400 (2) | C6—H6 | 0.95 |
C1—C6 | 1.401 (2) | C7—O1 | 1.216 (2) |
C2—C3 | 1.381 (2) | C7—O2 | 1.341 (2) |
C2—H2 | 0.95 | C8—O2 | 1.441 (2) |
C3—C4 | 1.393 (2) | C8—H8A | 0.98 |
C3—H3 | 0.95 | C8—H8B | 0.98 |
C4—C5 | 1.394 (2) | C8—H8C | 0.98 |
C4—C7 | 1.472 (2) | N1—H11 | 0.88 (2) |
C5—C6 | 1.377 (2) | N1—H12 | 0.91 (2) |
| | | |
N1—C1—C2 | 120.9 (1) | C5—C6—H6 | 119.7 |
N1—C1—C6 | 120.5 (1) | C1—C6—H6 | 119.7 |
C2—C1—C6 | 118.6 (1) | O1—C7—O2 | 122.2 (1) |
C3—C2—C1 | 120.4 (1) | O1—C7—C4 | 125.1 (1) |
C3—C2—H2 | 119.8 | O2—C7—C4 | 112.7 (1) |
C1—C2—H2 | 119.8 | O2—C8—H8A | 109.5 |
C2—C3—C4 | 120.9 (1) | O2—C8—H8B | 109.5 |
C2—C3—H3 | 119.6 | H8A—C8—H8B | 109.5 |
C4—C3—H3 | 119.6 | O2—C8—H8C | 109.5 |
C3—C4—C5 | 118.7 (1) | H8A—C8—H8C | 109.5 |
C3—C4—C7 | 119.0 (1) | H8B—C8—H8C | 109.5 |
C5—C4—C7 | 122.3 (1) | C1—N1—H11 | 117 (1) |
C6—C5—C4 | 120.8 (1) | C1—N1—H12 | 115 (1) |
C6—C5—H5 | 119.6 | H11—N1—H12 | 117 (2) |
C4—C5—H5 | 119.6 | C7—O2—C8 | 115.3 (1) |
C5—C6—C1 | 120.6 (1) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H11···O1i | 0.88 (2) | 2.08 (2) | 2.959 (2) | 175.1 (16) |
N1—H12···N1ii | 0.91 (2) | 2.37 (2) | 3.256 (2) | 164.4 (16) |
Symmetry codes: (i) x+1, y, z; (ii) −x+2, y−1/2, −z+1/2. |
Experimental details
Crystal data |
Chemical formula | C8H9NO2 |
Mr | 151.16 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 120 |
a, b, c (Å) | 8.5969 (4), 5.6053 (2), 15.5397 (7) |
β (°) | 96.172 (2) |
V (Å3) | 744.49 (6) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.10 |
Crystal size (mm) | 0.17 × 0.06 × 0.02 |
|
Data collection |
Diffractometer | Nonius KappaCCD diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 15706, 1313, 1040 |
Rint | 0.070 |
(sin θ/λ)max (Å−1) | 0.595 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.040, 0.104, 1.05 |
No. of reflections | 1313 |
No. of parameters | 108 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.17, −0.26 |
Selected geometric parameters (Å, º) topC1—N1 | 1.385 (2) | C7—O2 | 1.341 (2) |
C4—C7 | 1.472 (2) | C8—O2 | 1.441 (2) |
C7—O1 | 1.216 (2) | | |
| | | |
N1—C1—C2 | 120.9 (1) | O1—C7—O2 | 122.2 (1) |
N1—C1—C6 | 120.5 (1) | O1—C7—C4 | 125.1 (1) |
C3—C4—C7 | 119.0 (1) | O2—C7—C4 | 112.7 (1) |
C5—C4—C7 | 122.3 (1) | C7—O2—C8 | 115.3 (1) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H11···O1i | 0.88 (2) | 2.08 (2) | 2.959 (2) | 175.1 (16) |
N1—H12···N1ii | 0.91 (2) | 2.37 (2) | 3.256 (2) | 164.4 (16) |
Symmetry codes: (i) x+1, y, z; (ii) −x+2, y−1/2, −z+1/2. |
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Tuberculosis (TB) has re-emerged as one of the leading causes of death in the world, causing nearly 3 million deaths annually (Bloom & Murray, 1992). Although there are treatment regimens based on long-term and combined chemotherapy, the emergence of AIDS and the decline of socio-economic standards contribute to the disease's resurgence in industrialized countries and to the emergence of multidrug-resistant strains of Mycobacterium tuberculosis (Barnes et al., 1991). Therefore, the search for new therapeutics against tuberculosis is of utmost importance.
This work reports the structure of methyl-p-aminobenzoate (MAB), (I), an intermediate used to obtain benzoic acid-[(5-nitro-thiophen-2-yl-)methylene]-hydrazides, (II), (Fig. 1), which have sbeen hown to be active against tuberculosis (Rando et al., 2002). Since MAB is part of the synthesized benzohydrazide, a knowledge of its crystal-packing forces in addiction to its molecular geometry could be important in explaining some aspects of the activity of the final compound.
The crystal structure of (1), was determined in space group P21/c. Fig. 2 shows an ORTEP (Johnson, 1965) diagram of MAB. The molecule is almost flat: considering the non-H atoms, the largest deviations from the least-squares plane through the aromatic ring are 0.300 (3) and 0.180 (2) Å for atoms C8 and O2, respectively. The main geometrical parameters are given in Table 1. As expected, the observed geometry of the molecule agrees well with the geometries of similar derivatives (e.g. Elbasyouny et al., 1983; Peters et al., 1998; Lynch & McClenaghan, 2002).
Longarte et al. (1999) calculated the MAB ground-state structure and vibrational frequencies using the GAUSSIAN98W package (Frisch et al., 1998). Longarte et al. concluded that a sensible molecular–electronic description requires diffuse functions and polarizabilities in the theoretical calculations. In this way, they found that the NH2 H atoms form a 22.38° angle with the molecular plane, as expected (Kydd & Krueger, 1977; Hollas et al., 1983). In order to check Longarte et al.'s conclusion, the positional parameters of the two H atoms connected to the N atoms were not constrained during the refinements performed here. Our experimental data show that the dihedral angle between the NH2 groups and the aromatic ring plane are −25 (1) and 14 (1)° for H11—N1—C1—C6 and H12—N1—C1—C2, respectively, which confirm the results of Kydd & Krueger (1977) and Hollas et al. (1983). Comparison of the Longarte et al. (1999) 6–31+ G* model with our experimental MAB P21/c polymorphs by the Kabsch (1976) method showed them to be similar, with a r.m.s. deviation between analogous atoms of 0.064 Å.
The MAB structure has previously been determined by X-ray diffraction (Xianti, 1983) as belonging to space group C2/c [a = 16.242 (2) Å, b = 8.113 (2) Å, c = 12.724 (2) Å and β = 69.17 (1)°], while it is determined here as a new P21/c monoclinic polymorph. Comparison of these polymorphs by the Kabsch method (Kabsch, 1976) showed them to be very similar, with a r.m.s. deviation between analogous atoms of 0.043 Å. Therfore, the two polymorphs have the same molecular shape. The MAB P21/c polymorph found here exhibits two independent intermolecular hydrogen bonds (Fig. 3 and Table 2). Its packing is very similar to that observed in the monoclinic form of ethyl 4-aminobenzoate (benzocaine) determined by Lynch & McClenaghan (2002). The molecules are arranged head-to-tail, in linear ribbon arrays via N—H···O=C associations along the [100] direction. These ribbons form a herringbone structure, connected via N—H···N associations along the [010] direction. Therefore, the ribbons are themselves hydrogen-bonded, forming an infinite two-dimensional network parallel to the (001) plane. In the known C2/c polymorph, two independent hydrogen bonds form infinite chains along the [110] and [−110] directions. However, both take place via N—H···O=C associations, with N···O separations of about 3 Å.