3-Methyl-2-nitro­aniline

Bushra, F.A.; Bond, M.R.

doi:10.1107/S2414314626008394

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 11| Part 8| August 2026| x260839

https://doi.org/10.1107/S2414314626008394

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3-Methyl-2-nitroaniline

Fariha A. Bushra ^a and Marcus R. Bond ^a ^*

^aDepartment of Chemistry and Mathematics, 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 3 August 2026; accepted 14 August 2026; online 20 August 2026)

The structure of the title compound, C₇H₈N₂O₂, is reported and completes structural characterization for the family of methyl-2-nitroaniline isomers. Bond lengths and angles conform to reported values in other methyl-2-nitroaniline structures, except for the large angle [36.82 (4)°] formed between the phenyl ring and nitro group mean planes. This large angle is due to steric crowding by the neighboring methyl group, a result that is confirmed by an ab initio geometry optimization in vacuo that yields a similar interplanar angle (38.28°). In the extended structure, the molecules form inversion-related pairs that belong to neighboring supramolecular spiral stacks parallel to c. The stacks form around a 4₁ axis with N—H⋯N hydrogen bonding between molecules related by −1/4 of a turn at the core and peripheral N—H⋯O hydrogen bonds to molecules related by +3/4 of a turn.

Keywords: crystal structure; supramolecular helix; aniline.

CCDC reference: 2580961

Structure description

The title compound, C₇H₈N₂O₂ (I), is the only methyl-2-nitroaniline (M2NA) isomer with an unreported crystal structure. The geometric parameters of (I) (Fig. 1) conform to expected values and to the bond length and angle analysis conducted in our prior report of the structure of the 5-methyl isomer [Samson et al., 2025 ; Cambridge Structural Database (CSD) refcode: ILADOS]. Specifically, the aniline group is almost planar [root-mean-square deviation (r.m.s.d.) = 0.056 Å from the C1/N1/H1A/H1B mean plane] with slight pyramidalization (N1 deviates by 0.097 Å from the mean plane while other atoms deviate by ∼0.03 Å on the opposite side). The nitro group is essentially planar (r.m.s.d. = 0.002 Å from the C2/N2/O1/O2 mean plane). The aniline group is nearly coplanar with the phenyl ring [dihedral angle = 4.9 (4)° between mean-plane normals] but the nitro group is not [36.82 (4)° between mean plane normals]. This large interplanar angle results from steric crowding by the neighboring methyl group – in other M2NA structures this angle is less than 6°. This result is confirmed by an ab initio geometry optimization [6–31 G(d); GAMESS version 15 Jul 2024 (Schmidt et al., 1993 )] in which the value for this interplanar angle (38.26°) is in close agreement. Of note, a corresponding DFT geometry optimization [B3LYP, 6–31 G(d)] underestimates this angle (22.36°) but nevertheless shows the nitro group plane at a substantial twist. An electrostatic potential plot of the ab initio optimization is presented in Fig. 2 and the corresponding MOL file placed in supporting information.

Figure 1
Displacement ellipsoid plot of (I) at the 50% level with labels for all non-H atoms. The intramolecular hydrogen bond is indicated by a double-dashed line.

Figure 2
Electrostatic potential plot of the molecular geometry of (I) obtained from an ab initio geometry optimization. Regions of negative charge accumulation are colored red while regions of positive charge accumulation are colored blue. Atoms are drawn as spheres of arbitrary radii.

The C—N_a (a = aniline) distance in (I) is significantly shorter (by 0.16 Å) than the sum of the covalent radii. This result is expected due to participation of the aniline group in the π-system of the aromatic ring and in agreement with the average distance [1.349 (4) Å] in other M2NA structures. The C—N_n (n = nitro) distance is 0.07 Å less than the sum of the covalent radii and close to the average distance [1.46 (4) Å] in M2NA analogs as well as in the ab initio optimized geometry (1.454 Å). The large standard deviation in this average value is due to a bimodal distribution with distances of 1.50 Å in the 6-methyl analog [KEFYOK (Jing et al., 2006 ) and KEFYOK01/02 (Callear & Hursthouse, 2009 )] compared to distances in the range of 1.41–1.43 Å in the 4-methyl [TEHGUI (Ellena et al., 1996 ); TEGHUI01 (Cannon, Glidewell, Low et al., 2001 ); TEGHUI02 (Nigam & Murty, 1965 ); TEGHUI03 (Aguirre et al., 2024 )] and 5-methyl (ILADOS) compounds. A survey of 2-nitroaniline structures in the CSD (Version 6.01; February 2026 update; Groom et al., 2016 ) was conducted in which substitution was required in the 3-position on the aromatic ring and possible substitution at the other positions. Values of interplanar angles between phenyl and nitro groups and C—N_n bond lengths for 91 hits were recorded and show the full range of interplanar angles. Bond lengths generally increase with interplanar angles in spite of competing effects of other ring substituents (Fig. 3). These data can be empirically fitted by an exponential function that gives an interplanar angle of ∼26° for the C—N_n bond length in (I). The N—O distances agree within 0.004 Å and, with an average value of 1.218 Å, are significantly shorter that the sum of the covalent radii as a result of resonance between structures with a formal single and double bond. The shorter N—O distance belongs to the O atom involved in the intramolecular hydrogen bond.

Figure 3
A plot of the angle between phenyl and nitro group mean planes (°) versus C—N_nitro bond length (Å) for 3-substituted 2-nitroaniline structures. The red curve is an empirical exponential fit.

In the extended structure of (I), inversion-related pairs of molecules (Fig. 4), consisting of facing phenyl rings [centroid–centroid distance = 3.6498 (8) Å] slightly offset from each other [shift distance = 0.8407 (17) Å], are a readily observed structural motif. These molecules, however, belong to separate supramolecular spiral columns formed along the 4₁ screw axes (Fig. 5). Here the H atom involved in intramolecular hydrogen bonding also forms a long hydrogen bond to an aniline group on the preceding molecule related by −1/4 of a turn in the spiral. The sequence of N—H⋯N hydrogen bonds builds the spiral structure at the core of the column (Fig. 6). A shorter N—H⋯O hydrogen bond to the molecule 3/4 of a turn above provides a peripheral connection that reinforces the spiral structure. Four neighboring columns aggregate about a $[\overline{4}]$ axis (Fig. 7). Hydrogen-bonding parameters are presented in Table 1.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1B⋯O1	0.987 (15)	2.052 (15)	2.7126 (15)	122.5 (11)
N1—H1B⋯N1ⁱ	0.987 (15)	2.407 (15)	3.2705 (13)	145.8 (11)
N1—H1A⋯O2ⁱⁱ	0.955 (14)	2.285 (15)	3.2108 (15)	163.0 (13)
Symmetry codes: (i) $[-y+{\script{5\over 4}}, x-{\script{1\over 4}}, z-{\script{1\over 4}}]$ ; (ii) $[-y+{\script{5\over 4}}, x-{\script{1\over 4}}, z+{\script{3\over 4}}]$ .

Figure 4
Displacement ellipsoid plot of an inversion-related pair of molecules in (I). H atoms are drawn as spheres of arbitrary radii.

Figure 5
A plot of the supramolecular spiral structure generated by the 4₁ axis viewed with the c axis horizontal and [110] into the plane of the paper. Atoms are drawn as spheres of arbitrary radii and hydrogen bonds are indicated by dashed lines.

Figure 6
A plot of the molecular spiral viewed down the c axis with a horizontal and b vertical. Atoms are drawn as spheres of arbitrary radii and hydrogen bonds are indicated by dashed lines.

Figure 7
Packing diagram viewed down c with a vertical and b horizontal. 4₁ screw axes are denoted by red ‘+' symbols and $[\overline{4}]$ axes are denoted by solid red dots. Atoms are drawn as spheres of arbitrary radii.

The spiral columns in (I) are most closely related to the double spiral columns in KEFYOK/01. Here, pairs of facing, symmetrically inequivalent molecules are rotated by approximately 90° and moved up the column by a c-glide operation to generate an approximately square cross-section. Symmetrically inequivalent molecules related by 1/4 of a turn are connected pairwise with short N—H⋯O hydrogen bonds while longer N—H⋯O hydrogen bonds connect neighboring columns.

Synthesis and crystallization

3-Methyl-2-nitroaniline (99%, Ambeed) was separately dissolved in ethanol and in acetone. Orange diffraction-quality crystals were grown by slow evaporation. A crystal obtained from acetone solution provides the reported structure with no polymorphism found for crystals grown from ethanol solution. Crystals of 5-methyl-2-nitroaniline (ILADOS), previously obtained from ethanol solution, were grown from acetone solution but no polymorphic structure was found.

Refinement

Data collection and refinement parameters are presented in Table 2. Structure solution and initial refinement using an independent atom model occurred within SHELXL2018/3 (Sheldrick, 2015b ). 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. Two low angle reflections with F_o < F_c were presumed to be blocked by the beam catcher and omitted from the refinement. APEX3 software recommended data collection to 2θ_max = 66°. However <I/σ> < 3 for data beyond 2θ = 62°, so refinement was limited to 2θ_max = 62°.

Table 2
Experimental details

Crystal data
Chemical formula	C₇H₈N₂O₂
M_r	152.15
Crystal system, space group	Tetragonal, I4₁/a
Temperature (K)	295
a, c (Å)	19.8091 (6), 7.3503 (4)
V (Å³)	2884.3 (2)
Z	16
Radiation type	Mo Kα
μ (mm⁻¹)	0.11
Crystal size (mm)	0.38 × 0.36 × 0.21

Data collection
Diffractometer	Bruker D8 Quest Eco CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.910, 0.999
No. of measured, independent and observed [I ≥ 2u(I)] reflections	85493, 2296, 1669
R_int	0.087
(sin θ/λ)_max (Å⁻¹)	0.724

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.040, 0.075, 1.10
No. of reflections	2296
No. of parameters	172
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.31, −0.31
Computer programs: APEX3 and SAINT (Bruker, 2019 ), SHELXT2018/2 (Sheldrick, 2015a ), SHELXL2018/3 (Sheldrick, 2015b) OLEX2.refine (Bourhis et al., 2015 ), ORTEPIII (Burnett & Johnson, 1996 ), ORTEP-3 for Windows (Farrugia, 2012 ), Mercury 2026.1.1 (Macrae et al., 2020 ) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 2580961

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314626008394/hb4569sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314626008394/hb4569Isup2.hkl

MOL file for ab initio optimized geometry. DOI: https://doi.org/10.1107/S2414314626008394/hb4569sup3.mol

Supporting information file. DOI: https://doi.org/10.1107/S2414314626008394/hb4569Isup4.cml

checkCIF report

Computing details top

(I) top

Crystal data top

C₇H₈N₂O₂	D_x = 1.402 Mg m⁻³
M_r = 152.15	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4₁/a	Cell parameters from 9856 reflections
a = 19.8091 (6) Å	θ = 2.9–29.9°
c = 7.3503 (4) Å	µ = 0.11 mm⁻¹
V = 2884.3 (2) Å³	T = 295 K
Z = 16	Block, orange
F(000) = 1280	0.38 × 0.36 × 0.21 mm

Data collection top

Bruker D8 Quest Eco CCD diffractometer	1669 reflections with I ≥ 2u(I)
φ and ω scans	R_int = 0.087
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θ_max = 31.0°, θ_min = 3.6°
T_min = 0.910, T_max = 0.999	h = −30→30
85493 measured reflections	k = −30→30
2296 independent reflections	l = −11→11

Refinement top

Refinement on F²	0 constraints
Least-squares matrix: full	Primary atom site location: dual
R[F² > 2σ(F²)] = 0.040	All H-atom parameters refined
wR(F²) = 0.075	w = 1/[σ²(F_o²) + (0.0203P)² + 0.9459P] where P = (F_o² + 2F_c²)/3
S = 1.10	(Δ/σ)_max = 0.0002
2296 reflections	Δρ_max = 0.31 e Å⁻³
172 parameters	Δρ_min = −0.31 e Å⁻³
0 restraints

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

	x	y	z	U_iso*/U_eq
O1	0.64835 (4)	0.50497 (4)	0.26286 (11)	0.0554 (2)
O2	0.63080 (5)	0.60946 (4)	0.21656 (11)	0.0590 (3)
N1	0.65529 (6)	0.48114 (5)	0.62579 (18)	0.0470 (2)
H1A	0.6609 (8)	0.4522 (7)	0.729 (2)	0.070 (4)
H1B	0.6776 (8)	0.4679 (7)	0.511 (2)	0.064 (4)
N2	0.62245 (4)	0.55827 (4)	0.30605 (10)	0.03423 (19)
C1	0.60055 (5)	0.52243 (4)	0.62063 (13)	0.0311 (2)
C2	0.58132 (4)	0.56176 (4)	0.46892 (11)	0.02697 (18)
C3	0.52438 (5)	0.60431 (5)	0.46971 (13)	0.0334 (2)
C4	0.48708 (6)	0.60780 (6)	0.62847 (17)	0.0454 (3)
H4	0.4425 (7)	0.6385 (8)	0.630 (2)	0.085 (5)
C5	0.50662 (6)	0.57207 (6)	0.78302 (16)	0.0496 (3)
H5	0.4765 (7)	0.5758 (8)	0.905 (2)	0.084 (5)
C6	0.56209 (6)	0.53066 (6)	0.78023 (15)	0.0430 (3)
H6	0.5777 (7)	0.5026 (7)	0.8943 (19)	0.076 (4)
C31	0.50038 (8)	0.64390 (9)	0.3083 (2)	0.0539 (3)
H31A	0.5285 (10)	0.6878 (9)	0.289 (2)	0.095 (6)
H31B	0.5014 (11)	0.6159 (9)	0.185 (2)	0.113 (7)
H31C	0.4505 (9)	0.6590 (9)	0.329 (2)	0.112 (6)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0697 (6)	0.0555 (5)	0.0411 (4)	0.0169 (4)	0.0181 (4)	−0.0051 (4)
O2	0.0723 (6)	0.0585 (5)	0.0463 (5)	0.0022 (4)	0.0238 (4)	0.0179 (4)
N1	0.0532 (6)	0.0453 (6)	0.0425 (6)	0.0100 (5)	0.0002 (5)	0.0128 (5)
H1A	0.095 (12)	0.056 (9)	0.058 (10)	0.010 (8)	−0.011 (8)	0.020 (8)
H1B	0.085 (12)	0.062 (10)	0.046 (9)	0.022 (8)	0.003 (9)	0.004 (8)
N2	0.0370 (4)	0.0406 (5)	0.0251 (4)	−0.0009 (4)	0.0043 (3)	0.0006 (3)
C1	0.0364 (5)	0.0301 (5)	0.0269 (4)	−0.0054 (4)	0.0016 (4)	0.0023 (4)
C2	0.0302 (4)	0.0262 (4)	0.0245 (4)	−0.0032 (3)	0.0024 (3)	−0.0020 (3)
C3	0.0311 (5)	0.0328 (5)	0.0363 (5)	−0.0001 (4)	−0.0009 (4)	−0.0052 (4)
C4	0.0365 (6)	0.0483 (6)	0.0514 (7)	0.0001 (5)	0.0101 (5)	−0.0147 (5)
H4	0.068 (10)	0.088 (11)	0.099 (12)	0.016 (9)	0.010 (9)	−0.026 (9)
C5	0.0496 (7)	0.0608 (7)	0.0385 (6)	−0.0103 (6)	0.0186 (5)	−0.0122 (5)
H5	0.089 (11)	0.103 (12)	0.062 (10)	−0.008 (9)	0.025 (9)	−0.005 (9)
C6	0.0525 (7)	0.0496 (6)	0.0269 (5)	−0.0121 (5)	0.0073 (5)	0.0029 (5)
H6	0.100 (11)	0.085 (10)	0.044 (8)	−0.004 (9)	0.019 (8)	−0.001 (8)
C31	0.0511 (8)	0.0531 (8)	0.0575 (8)	0.0121 (6)	−0.0122 (7)	0.0071 (7)
H31A	0.123 (15)	0.059 (10)	0.104 (14)	0.007 (10)	−0.021 (11)	0.024 (10)
H31B	0.167 (19)	0.114 (15)	0.059 (11)	0.055 (13)	−0.029 (12)	−0.010 (11)
H31C	0.063 (11)	0.151 (16)	0.121 (15)	0.049 (11)	−0.003 (10)	0.041 (13)

Geometric parameters (Å, º) top

O1—N2	1.2160 (10)	C3—C31	1.4995 (16)
O2—N2	1.2199 (10)	C4—H4	1.073 (14)
N1—H1A	0.955 (14)	C4—C5	1.3933 (18)
N1—H1B	0.987 (15)	C5—H5	1.082 (14)
N1—C1	1.3588 (14)	C5—C6	1.3714 (18)
N2—C2	1.4497 (11)	C6—H6	1.052 (15)
C1—C2	1.4125 (12)	C31—H31A	1.042 (18)
C1—C6	1.4082 (14)	C31—H31B	1.066 (17)
C2—C3	1.4081 (12)	C31—H31C	1.044 (16)
C3—C4	1.3830 (14)

H1B—N1—H1A	117.6 (12)	H4—C4—C3	118.5 (9)
C1—N1—H1A	118.5 (9)	C5—C4—C3	120.94 (11)
C1—N1—H1B	119.6 (8)	C5—C4—H4	120.6 (9)
O2—N2—O1	121.58 (8)	H5—C5—C4	119.3 (8)
C2—N2—O1	119.61 (8)	C6—C5—C4	120.95 (11)
C2—N2—O2	118.81 (8)	C6—C5—H5	119.7 (8)
C2—C1—N1	124.70 (9)	C5—C6—C1	121.00 (11)
C6—C1—N1	118.56 (10)	H6—C6—C1	116.4 (7)
C6—C1—C2	116.61 (9)	H6—C6—C5	122.6 (7)
C1—C2—N2	118.30 (8)	H31A—C31—C3	111.8 (9)
C3—C2—N2	118.82 (8)	H31B—C31—C3	113.4 (8)
C3—C2—C1	122.88 (8)	H31B—C31—H31A	108.2 (14)
C4—C3—C2	117.48 (9)	H31C—C31—C3	109.4 (9)
C31—C3—C2	124.32 (10)	H31C—C31—H31A	106.7 (13)
C31—C3—C4	118.17 (11)	H31C—C31—H31B	107.0 (14)

O1—N2—C2—C1	35.82 (10)	N2—C2—C3—C31	3.80 (12)
O1—N2—C2—C3	−144.56 (9)	C1—C2—C3—C4	1.11 (10)
O2—N2—C2—C1	−143.35 (9)	C1—C2—C3—C31	−176.61 (11)
O2—N2—C2—C3	36.26 (10)	C1—C6—C5—C4	−0.68 (12)
N1—C1—C2—N2	0.04 (11)	C2—C1—C6—C5	3.55 (10)
N1—C1—C2—C3	−179.55 (10)	C2—C3—C4—C5	1.98 (10)
N1—C1—C6—C5	179.56 (10)	C3—C2—C1—C6	−3.81 (10)
N2—C2—C1—C6	175.79 (8)	C3—C4—C5—C6	−2.23 (13)
N2—C2—C3—C4	−178.49 (8)	C5—C4—C3—C31	179.84 (12)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1B···O1	0.987 (15)	2.052 (15)	2.7126 (15)	122.5 (11)
N1—H1B···N1ⁱ	0.987 (15)	2.407 (15)	3.2705 (13)	145.8 (11)
N1—H1A···O2ⁱⁱ	0.955 (14)	2.285 (15)	3.2108 (15)	163.0 (13)

Symmetry codes: (i) −y+5/4, x−1/4, z−1/4; (ii) −y+5/4, x−1/4, z+3/4.

Acknowledgements

Quantum mechanical calculations were conducted on the CIMUSE nodes funded by National Science Foundation grant 2322084 and incorporated as part of the Hellbender high performance computing environment at the University of Missouri-Columbia.

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