5-Methyl-2-nitro­aniline

Samson, L.; Banwart, L.; Silwal, S.; Bond, M.R.

doi:10.1107/S2414314625007473

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 10| Part 8| August 2025| x250747

https://doi.org/10.1107/S2414314625007473

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5-Methyl-2-nitroaniline

Lily Samson,^a Lydia Banwart,^a Sajan Silwal ^a and Marcus R. Bond ^a ^*

^aDepartment of Chemistry and Physics, Southeast Missouri State University, Cape Girardeau, MO 63701, USA
^*Correspondence e-mail: [email protected]

Edited by W. T. A. Harrison, University of Aberdeen, United Kingdom (Received 15 August 2025; accepted 20 August 2025; online 27 August 2025)

The bond lengths and angles within the title molecule, C₇H₈N₂O₂, conform to average values for other 5-substituted-2-nitroanilines, and with those calculated by a DFT geometry optimization. The short C—NH₂ bond length of 1.3469 (12) Å is indicative of substantial involvement of the aniline N-atom in the aromatic π bonding system of the ring. In the extended structure, N—H⋯O hydrogen bonds link the molecules into [001] tapes, which aggregate into zipper-like folded ribbons. Layers of parallel ribbons stack along a to complete the structure.

Keywords: crystal structure; hydrogen bonding; DFT geometry optimization.

CCDC reference: 2481714

Structure description

The title molecule, C₇H₈N₂O₂ (I), is approximately planar with the ring C atoms exhibiting an average deviation of 0.003 (2) Å from the mean plane (Fig. 1). The molecular plane lies closest to the bc plane of the unit cell but is canted to form an angle of 17.25° between normals. The geometry about both N atoms is almost planar so that sp² hybridization can be reasonably assigned. The aniline nitrogen atom (N1) shows the most pyramidalization with a distance of 0.0792 (1) Å of this atom from the mean plane of its attached H atoms and C1, versus 0.0005 (1) Å for N2. The amino and nitro group planes make twist angles of 5.1 (7) and 3.87 (4)°, respectively, with respect to the mean plane of the C1–C6 ring. One H atom of the amine group makes an intramolecular hydrogen bond to an O atom of the nitro group (Table 1). The nitro group geometry is uniform with the N—O distances agreeing within 1 s.u. of each other, and in agreement with the mean N—O bond length for 5-substituted-2-nitroanilines reported in the Cambridge Structural Database [1.233 (23) Å; 35 hits, CSD version 5.45, June 2024 update; Groom et al., 2016 ]. Other geometrical parameters agree well with average values from the CSD. The nitro group bond angles are close to 120° with the O—N—O angle slightly larger [121.20 (9)° for O—N—O and 119.4 (9)° for C—N—O for CSD mean values]. The C1—N1 bond length of 1.3469 (12) Å in (I) is significantly shorter than the sum of the covalent radii of 1.44 Å but similar to the CSD mean of 1.341 (25) Å for a C_ar—NH₂ bond, a familiar situation in aniline compounds where the nominal lone pair of the nitrogen atom participates in the aromatic π-bonding network of the ring (Morrison & Boyd, 1976 ). The C2—N2 distance to the nitro group is only slightly shorter than the sum of the covalently radii [CSD mean = 1.422 (25) Å].

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H2⋯O2	0.987 (14)	1.934 (14)	2.6356 (15)	125.7 (10)
N1—H1⋯O1ⁱ	0.968 (13)	2.133 (13)	3.0897 (14)	169.4 (12)
Symmetry code: (i) .

Figure 1
Displacement ellipsoid plot at the 50% probability level of (I) with atom labels. The intramolecular N—H⋯O hydrogen bond is indicated by a dashed line.

A DFT geometry optimization of the title molecule in vacuo [B3LYP, 6311+G(d,p); GAMESS (Schmidt et al., 1993 )] provides geometric parameters in broad agreement with experimental values. Of note, the optimized aniline C—N distance is only 0.01 Å longer than the experimental value. In addition, there is significant contribution of the p-orbital on the N atom to the delocalized π-bonding system of the aromatic ring in the highest occupied molecular orbital (HOMO), as shown in the plot in Fig. 2. The nitro group exhibits the greatest deviation from the experimental values with the C—N bond longer by 0.024 Å and unequal N—O bond lengths (the O atom involved in intramolecular hydrogen bonding is 0.016 Å longer). A MOL file containing the optimized geometry is available in supporting information.

Figure 2
Plot of the highest occupied molecular orbital for (I) from the DFT geometry optimization.

In the extended structure of (I), intermolecular hydrogen bonding between H1 and O1 of a neighboring molecule links molecules into tapes propagating parallel to c. The opposite polarity of the amino- and nitro- groups, as shown in the electrostatic potential plot in Fig. 3, generates a zipper-like folded ribbon between two neighboring tapes to place groups of opposite polarity in neighboring tapes in close proximity. The hydrophobic methyl groups from neighboring ribbons abut to generate corrugated sheets in the bc plane. These sheets are stacked along a with only slight overlap between phenyl rings in neighboring sheets and with the fold of polar groups in one sheet overlying the fold of hydrophobic groups in the neighboring sheets. A table of hydrogen-bond parameters is presented in Table 1, a packing diagram for a single sheet is presented in Fig. 4, and a unit-cell packing diagram is presented in Fig. 5.

Figure 3
Electrostatic potential plot for (I) from the DFT geometry optimization. Red indicates accumulation of negative charge and blue accumulation of positive charge.

Figure 4
Packing diagram for a corrugated sheet of molecules of (I) viewed down a with b horizontal and c vertical. Atoms are drawn as circles of arbitrary radii, intramolecular hydrogen bonds are indicated by thick dashed lines, and intermolecular hydrogen bonds are indicated by thin dashed lines.

Figure 5
Unit-cell packing diagram for (I) viewed down c with a vertical and b horizontal. Atoms are drawn as circles of arbitrary radii.

Other known methyl-2-nitroanilines exhibit polymorphs with different hydrogen-bonding arrangements. For the 4-methyl derivative, two polymorphs crystallized from different solvents are known. The first is in monoclinic C2/c with Z′ = 1 (CSD refcode TEHGUI/02; Ellena et al., 1996 ; Nigam & Murty, 1965 ; from ethanol) while the other is in triclinic P $[\overline{1}]$ with Z′ = 2 (TEHGUI01/03; Cannon et al., 2001 ; Aguirre et al., 2024 ; from acetone). The 6-methyl derivative likewise occurs in two polymorphs. Both crystallize in monoclinic P2₁/c but differ in unit-cell volumes by a factor of approximately 2 [KEFYOK (Jing et al., 2006 ) and KEFYOK01/KEFYOK02 (Callear & Hursthouse, 2009 )]. The Z′ = 2 polymorph is crystallized from N,N-dimethylformamide (KEFYOK) or methanol/imidazolidine-2-thione (KEFYOK01) while the Z′ = 1 polymorph crystallizes from methanol/benzenesulfonic acid. The structure of the 3-methyl derivative remains unreported while a systematic search for polymorphs of the title compound has not been conducted.

Bifurcated N—H⋯(O,O) hydrogen bonding from an amino proton to the nitro O atoms is a common motif in the structures of 2-nitro anilines. Asymmetric bifurcated hydrogen bonding is observed in KEFYOK/01 and TEHGUI, while a mix of symmetric, bifurcated hydrogen bonding and direct hydrogen bonding is found for symmetry-unique molecules in TEHGUI01. Extended molecular arrangements in these structures consist of spiral, square columns in KEFYOK/01 but planar layers in TEHGUI and TEHGUI01. The extended structure of KEFYOK02 provides the greatest similarity to the title compound with direct intermolecular N—H⋯O hydrogen bonding linking molecules into corrugated layers, albeit with hydrogen bonding now between molecules on opposite sides of the corrugation fold. Placement of the methyl group adjacent to the amino group eliminates the need for a hydrophobic fold, as in the title structure, but also results in a longer H⋯O hydrogen bond contact distance of 2.32 Å.

Synthesis and crystallization

5-Methyl-2-nitroaniline (99.9%, AmBeed) was recrystallized from ethanol solution by slow evaporation to yield diffraction-quality crystals.

Refinement

Crystal data, data collection, and structure refinement details are listed in Table 2. Structure solution and initial refinement using an independent atom model occurred within the Bruker SHELXTL software package (Version 2016/6). A disordered model for the methyl H atoms resulted in a higher agreement factor, thus the ordered model was retained. Final structure refinement occurred within the OLEX2–1.5 system via Hirshfeld atom refinement using NoSpherA2 (Kleemiss et al., 2021 ; Midgley et al., 2021 ) with non-spherical atomic form factors derived from electron density determined by DFT calculations using ORCA 5.0 (B3LYP functional, def2-SVP basis set; Neese, 2022). All atoms were refined anisotropically. This resulted in a slightly underdetermined data:parameter ratio (9.83:1) as a consequence of pursuing the non-spherical refinement. Four low angle reflections with F_o << F_c were presumed to be blocked by the beam catcher and omitted from the refinement.

Table 2
Experimental details

Crystal data
Chemical formula	C₇H₈N₂O₂
M_r	152.15
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	295
a, b, c (Å)	7.4151 (7), 15.8116 (16), 7.1225 (7)
β (°)	118.524 (3)
V (Å³)	733.71 (13)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.10
Crystal size (mm)	0.23 × 0.21 × 0.10

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.670, 0.746
No. of measured, independent and observed [I ≥ 2σ(I)] reflections	19599, 1700, 1311
R_int	0.035
(sin θ/λ)_max (Å⁻¹)	0.651

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.033, 0.055, 1.12
No. of reflections	1700
No. of parameters	173
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.18, −0.13
Computer programs: APEX3 and SAINT (Bruker, 2017 ), SHELXT2018/2 (Sheldrick, 2015a ), OLEX2.refine (Bourhis et al., 2015 ) SHELXL2018/3 (Sheldrick, 2015b ), ORTEP-3 for Windows 2020.1 (Farrugia, 2012 ), ORTEPIII (Burnett & Johnson, 1996 ), OLEX2 (Dolomanov et al., 2009 ), publCIF (Westrip, 2010 ) and PARST (Nardelli, 1995 ).

Structural data

CCDC reference: 2481714

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314625007473/hb4532sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314625007473/hb4532Isup2.hkl

MOL file from quantum mechanical geometry optimization. DOI: https://doi.org/10.1107/S2414314625007473/hb4532sup3.mol

Supporting information file. DOI: https://doi.org/10.1107/S2414314625007473/hb4532Isup4.cml

checkCIF report

Computing details top

5-Methyl-2-nitroaniline top

Crystal data top

C₇H₈N₂O₂	F(000) = 320.241
M_r = 152.15	D_x = 1.377 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.4151 (7) Å	Cell parameters from 7279 reflections
b = 15.8116 (16) Å	θ = 2.6–26.9°
c = 7.1225 (7) Å	µ = 0.10 mm⁻¹
β = 118.524 (3)°	T = 295 K
V = 733.71 (13) Å³	Irregular, yellow
Z = 4	0.23 × 0.21 × 0.10 mm

Data collection top

Bruker APEXII CCD diffractometer	1311 reflections with I ≥ 2σ(I)
φ and ω scans	R_int = 0.035
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θ_max = 27.6°, θ_min = 3.5°
T_min = 0.670, T_max = 0.746	h = −9→9
19599 measured reflections	k = −20→20
1700 independent reflections	l = −9→9

Refinement top

Refinement on F²	Primary atom site location: dual
Least-squares matrix: full	All H-atom parameters refined
R[F² > 2σ(F²)] = 0.033	w = 1/[σ²(F_o²) + (0.0097P)² + 0.0677P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.055	(Δ/σ)_max = 0.0004
S = 1.12	Δρ_max = 0.18 e Å⁻³
1700 reflections	Δρ_min = −0.13 e Å⁻³
173 parameters	Extinction correction: Zachariasen, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.027 (3)
0 constraints

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
N1	0.66254 (18)	0.62975 (7)	0.90340 (19)	0.0615 (3)
H1	0.675 (2)	0.6288 (8)	1.045 (2)	0.091 (5)
H2	0.661 (2)	0.6839 (9)	0.834 (2)	0.084 (5)
C1	0.70816 (13)	0.55938 (5)	0.82802 (12)	0.0392 (2)
C2	0.73877 (13)	0.55572 (5)	0.64725 (12)	0.0396 (2)
N2	0.72344 (13)	0.62938 (6)	0.52484 (12)	0.0551 (2)
O1	0.76280 (14)	0.62386 (6)	0.37703 (13)	0.0905 (3)
O2	0.67125 (14)	0.69659 (5)	0.56884 (13)	0.0803 (3)
C3	0.78714 (15)	0.47926 (6)	0.58181 (16)	0.0496 (3)
H3	0.8103 (18)	0.4805 (7)	0.4418 (18)	0.082 (4)
C4	0.80415 (16)	0.40613 (7)	0.69101 (17)	0.0553 (3)
H4	0.842 (2)	0.3482 (7)	0.6426 (19)	0.100 (4)
C5	0.77246 (14)	0.40677 (6)	0.87032 (15)	0.0503 (3)
C51	0.7879 (3)	0.32578 (11)	0.9867 (3)	0.0807 (5)
H51a	0.792 (4)	0.3353 (11)	1.130 (3)	0.152 (9)
H51b	0.669 (3)	0.2851 (10)	0.901 (3)	0.168 (9)
H51c	0.927 (3)	0.2944 (10)	1.030 (4)	0.149 (8)
C6	0.72643 (15)	0.48186 (6)	0.93469 (15)	0.0459 (2)
H6	0.7037 (17)	0.4837 (6)	1.0718 (17)	0.077 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.0848 (7)	0.0497 (6)	0.0571 (6)	0.0121 (5)	0.0395 (6)	−0.0076 (5)
H1	0.125 (12)	0.087 (10)	0.073 (9)	0.007 (8)	0.058 (9)	−0.021 (8)
H2	0.106 (11)	0.064 (9)	0.078 (10)	0.014 (9)	0.042 (8)	0.012 (8)
C1	0.0478 (5)	0.0363 (5)	0.0351 (4)	0.0018 (4)	0.0212 (4)	−0.0017 (4)
C2	0.0451 (5)	0.0400 (5)	0.0341 (4)	−0.0007 (4)	0.0193 (4)	0.0004 (4)
N2	0.0615 (6)	0.0553 (5)	0.0456 (5)	−0.0038 (4)	0.0231 (4)	0.0142 (4)
O1	0.1153 (7)	0.1071 (7)	0.0678 (5)	0.0005 (5)	0.0588 (5)	0.0299 (5)
O2	0.1099 (7)	0.0440 (4)	0.0839 (6)	0.0059 (4)	0.0437 (5)	0.0219 (4)
C3	0.0590 (6)	0.0520 (6)	0.0431 (5)	0.0012 (5)	0.0286 (5)	−0.0096 (5)
H3	0.110 (10)	0.086 (9)	0.074 (8)	0.006 (7)	0.064 (8)	−0.011 (7)
C4	0.0630 (7)	0.0389 (6)	0.0619 (6)	0.0029 (5)	0.0282 (5)	−0.0108 (5)
H4	0.131 (11)	0.059 (8)	0.113 (10)	0.013 (7)	0.060 (9)	−0.027 (7)
C5	0.0496 (5)	0.0367 (5)	0.0575 (6)	−0.0019 (4)	0.0199 (5)	0.0058 (4)
C51	0.0763 (11)	0.0490 (9)	0.1010 (12)	−0.0029 (7)	0.0296 (10)	0.0278 (8)
H51a	0.23 (2)	0.089 (13)	0.143 (16)	−0.003 (14)	0.093 (17)	0.043 (12)
H51b	0.113 (14)	0.101 (12)	0.20 (2)	−0.055 (11)	0.005 (12)	0.060 (12)
H51c	0.102 (14)	0.101 (12)	0.24 (2)	0.036 (10)	0.075 (14)	0.080 (13)
C6	0.0538 (6)	0.0460 (6)	0.0412 (5)	0.0000 (4)	0.0252 (5)	0.0061 (4)
H6	0.106 (9)	0.073 (8)	0.066 (7)	0.005 (6)	0.051 (7)	0.019 (6)

Geometric parameters (Å, º) top

N1—H1	0.968 (13)	C3—C4	1.3653 (14)
N1—H2	0.987 (14)	C4—H4	1.062 (10)
N1—C1	1.3469 (12)	C4—C5	1.4046 (14)
C1—C2	1.4113 (11)	C5—C51	1.4997 (16)
C1—C6	1.4141 (12)	C51—H51a	1.021 (19)
C2—N2	1.4265 (11)	C51—H51b	1.025 (15)
N2—O1	1.2225 (10)	C51—H51c	1.048 (16)
N2—O2	1.2220 (11)	C5—C6	1.3732 (13)
C2—C3	1.4025 (12)	C6—H6	1.068 (10)
C3—H3	1.090 (10)

H1—N1—H2	120.7 (11)	C3—C4—H4	120.8 (7)
C1—N1—H1	119.0 (8)	C5—C4—H4	119.1 (7)
C1—N1—H2	117.5 (8)	C3—C4—C5	120.12 (10)
C2—C1—N1	125.31 (9)	C4—C5—C51	119.64 (13)
C6—C1—N1	118.67 (9)	C6—C5—C51	121.29 (13)
C6—C1—C2	116.02 (8)	C4—C5—C6	119.08 (9)
C1—C2—N2	121.56 (8)	C5—C51—H51a	112.7 (11)
C1—C2—C3	121.11 (8)	C5—C51—H51b	113.0 (9)
C3—C2—N2	117.32 (8)	C5—C51—H51c	111.8 (9)
O1—N2—C2	119.07 (9)	H51a—C51—H51b	107.0 (14)
O2—N2—C2	119.73 (8)	H51a—C51—H51c	102.8 (14)
O1—N2—O2	121.20 (9)	H51b—C51—H51c	108.9 (14)
C2—C3—H3	117.7 (6)	C5—C6—C1	123.05 (9)
C4—C3—H3	121.6 (6)	C1—C6—H6	116.9 (5)
C2—C3—C4	120.62 (9)	C5—C6—H6	120.1 (5)

N1—C1—C2—N2	0.08 (11)	C1—C6—C5—C4	0.30 (11)
N1—C1—C2—C3	179.60 (10)	C1—C6—C5—C51	−179.25 (12)
N1—C1—C6—C5	−179.98 (9)	C2—C3—C4—C5	0.23 (11)
C1—C2—N2—O1	175.85 (9)	C3—C4—C5—C51	178.91 (12)
C1—C2—N2—O2	−4.24 (10)	C3—C4—C5—C6	−0.65 (12)
C1—C2—C3—C4	0.54 (10)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H2···O2	0.987 (14)	1.934 (14)	2.6356 (15)	125.7 (10)
N1—H1···O1ⁱ	0.968 (13)	2.133 (13)	3.0897 (14)	169.4 (12)

Symmetry code: (i) x, y, z+1.

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