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In 2,4,6-trimethyl-N-nitro­aniline (alternatively called mesitylnitramine), C9H12N2O2, the primary nitramino group is planar with a short N—N bond and is nearly perpendicular to the aromatic ring. The methyl group located in the para position is disordered, each H atom having half-occupancy. The mol­ecules are linked together along the [100] axis by inter­molecular N—H...O hydrogen bonds.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270106055776/hj3024sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270106055776/hj3024Isup2.hkl
Contains datablock I

CCDC reference: 638333

Comment top

A common feature of primary and secondary N-arylnitramines is their ability to rearrange to the corresponding ortho and para amino–nitro compounds under the influence of an acid (Banthorpe & Thomas, 1965). The molecular structure of N-methyl-N-phenylnitramine and its ring–substituted derivatives are well elucidated. The geometric parameters of the nitramino group, in particular a long Ar—N bond, a short N—N bond and a large torsion angle on the Ar—N bond, are not influenced by the ring substituents (Daszkiewicz et al., 2000, 2002). The results were unexpected since migration of the N-nitro group to the ring requires a nearly coplanar conformation of a nitramine molecule. The geometry of the primary nitramino group was not so frequently studied, and in most examples the NHNO2 group is connected to an electron deficient ring, as shown in scheme 1.

The nitramino group in mesitylnitramine, (I), is nearly planar, and the sum of valence angles [358.0 (12)°] around N7 indicates trigonal hybridization of the amide N atom. However, N7 deviates from the C1/H7/N8 plane by 0.100 (2) Å. The small torsion angle along the N—N bond is 4.4 (11)° (averaged) and may result from non-valence interactions. The N7—N8 bond length [1.3405 (17) Å] also indicates high bond order. The differences in respect to the other nitramines (II)–(IV) are small [0.025 (1) Å maximum] but they correspond to the differences in the lengths of Ar—N bonds. In pyridine derivatives (III) and (IV), these bonds are more than 0.05 Å shorter (Zaleski et al., 2001) than in (I). This may be interpreted as the result of a change in the π-electron distribution, within the nitramino group, under the influence of the electron deficient ring.

The conformations of the molecules confirm the conclusion. In (I), the torsion angle along the C1—N7 bond (ca 83.4°) may be caused by the steric hindrance, but in (II), the nitramine group is twisted by approximately 22 and 44° for the two independent molecules (Zaleski et al., 2002). In contrast, in (III) and (IV), the nitramine groups are nearly coplanar with the pyridine ring, indicating conjugation between both π-electron systems. The geometry of aromatic ring in (I) is not disturbed by the relatively large number of substituents. The difference of a particular C—C bond length and averaged value (1.388 Å) does not exceed 0.007 Å. At room temperature, the methyl group in the para position rotates along the C—C axis, this being observed as a splitting of the H-atom positions. A decrease of the temperature causes destruction of the crystal as a result of a phase transition.

In the IR spectrum of (I), a strong and broad band, with the maximum at 3226 cm-1, indicates the presence of a hydrogen bond. Despite the acidic properties of primary nitramines, the interaction is weak, as indicated by the long donor–acceptor distance (Table 2). The molecules are joined together along the a axis via the hydrogen bond, but ππ stacking interaction seems to be a decisive factor in the molecular packing (Fig. 2). The molecules are arranged parallel in columns. Each molecule is 3.524 (2) Å distant from its neighbours and twisted by 180°. The angle between the molecules belonging to neighbouring stacks is 41.4 (11)°. In the crystal network of (II), the hydrogen bond is addressed to the p-nitro group (Zaleski et al., 2002). Comparison of (I) and (II) indicates that the O atom of the nitramine group is a very poor proton acceptor. Analogously, the crystal structure of N,N–dinitroethylenediamine is determined by the local dipole – dipole interactions in spite of the weak (3.007 Å) N—H···O hydrogen bond (Turley, 1968).

The geometry of the primary and secondary N-arylnitramines is similar in the most characteristic aspects. The environment of amide atom N7 indicates its trigonal hybridization and high N—N bond order. The planar nitramino group is bonded to the benzene ring with a relatively long C—N bond and twisted with resepct to the nearly perpendicular position. Such a conformation is an effect of a steric interaction between N–methyl or Ar–methyl groups and the neighbouring substituent.

Related literature top

For related literature, see: Banthorpe & Thomas (1965); Daszkiewicz et al. (2000, 2002); Turley (1968); Zaleski et al. (2001, 2002).

Experimental top

Ethyl bromide (2.3 ml, 30 mmol), diluted with absolute diethyl ether (15 ml), was added dropwise to a stirred suspension of magnesium turnings (1.20 g, 50 mmol) in ether (50 ml). A solution of ethylmagnesium bromide was filtered into 2,4,6-trimethylaniline (2.70 g, 20 mmol) dissolved in dry toluene (100 ml). The mixture was stirred and refluxed for 1 h. It was cooled to room temperature, n-butyl nitrate (3.60 g, 30 mmol) was added and stirring was continued for 1 h. Water (30 ml) and acetic acid (2 ml) were added to the mixture, and the aqueous layer was separated and discarded. The nitramine was extracted (3 × 30 ml) from ethereal solution with 1M aqueous potassium hydroxide, and precipitated by careful acidification (273 K) with 3M hydrochloric acid. The crude product was collected by filtration, dried in vacuum and crystallized from n-hexane. N-(2,4,6-Trimethyl)nitramine (1.60 g, 44%) was obtained as colourless crystals, melting at 386–388 K. Crystals suitable for X-ray diffraction studies were obtained by a slow evaporation of the 1:1 n-hexane–diethyl ether solution at room temperature. IR (KBr, ν, cm-1): 3226 (NH proton, stretching vibrations); 1593, 1326 (N—NO2, asymmetric and symmetric stretch). 1H NMR (CDCl3, p.p.m.): δ 9.58 (s, 1H, nitramine H atom), 6.95 (s, 2H, aromatic H atoms), 2.30 (s, 3H, para-methyl group), 2.24 (s, 6H, ortho-methyl groups). 13C NMR (CDCl3, p.p.m.): δ 140.7 (C-1), 137.1 (C-2 and C-6), 129.6 (C-3 and C-5), 129.4 (C-4), 21.3 (para-CH3), 17.9 (ortho-CH3).

Differential scanning calorimetry studies showed that mesitylnitramine undergoes a strong first-order phase transition at 230 K on cooling and 270 K on heating with ΔH = 0.4 kJ mol-1 and ΔS = 1.6 J K mol-1. The single-crystal at the phase transition is destroyed to powder.

Refinement top

The H atoms of the phenyl rings and the H atom bonded to N7 were freely refined; the C—H bond lengths are 0.937 (17) and 0.941 (18) Å, and the N—H bond length is 0.874 (18) Å. The H atoms of the CH3 groups were placed in calculated positions (C—H = 0.98 Å). The methyl group in the para position is disordered with the site occupation factor 0.5.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2002 ??2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2002 ??2006); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1990); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The molecular structure of (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
[Figure 2] Fig. 2. The packing of mesitylnitramine viewed down c, showing the hydrogen-bonding scheme (dashed lines). Displacement ellipsoids are drawn at the 50% probability level.
2,4,6-trimethyl-N-nitroaniline top
Crystal data top
C9H12N2O2F(000) = 768
Mr = 180.21Dx = 1.210 Mg m3
Orthorhombic, PbcaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2abCell parameters from 2650 reflections
a = 7.6217 (6) Åθ = 3.2–29.6°
b = 15.8538 (13) ŵ = 0.09 mm1
c = 16.3696 (12) ÅT = 295 K
V = 1978.0 (3) Å3Plate, colourless
Z = 80.30 × 0.25 × 0.15 mm
Data collection top
Oxford Diffraction Xcalibur
diffractometer
1329 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.038
Graphite monochromatorθmax = 29.6°, θmin = 3.2°
Detector resolution: 8.2765 pixels mm-1h = 107
ω scansk = 2121
14835 measured reflectionsl = 2222
2650 independent reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.046Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.142H atoms treated by a mixture of independent and constrained refinement
S = 0.98 w = 1/[σ2(Fo2) + (0.0662P)2]
2650 reflections(Δ/σ)max = 0.018
136 parametersΔρmax = 0.14 e Å3
0 restraintsΔρmin = 0.18 e Å3
Crystal data top
C9H12N2O2V = 1978.0 (3) Å3
Mr = 180.21Z = 8
Orthorhombic, PbcaMo Kα radiation
a = 7.6217 (6) ŵ = 0.09 mm1
b = 15.8538 (13) ÅT = 295 K
c = 16.3696 (12) Å0.30 × 0.25 × 0.15 mm
Data collection top
Oxford Diffraction Xcalibur
diffractometer
1329 reflections with I > 2σ(I)
14835 measured reflectionsRint = 0.038
2650 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0460 restraints
wR(F2) = 0.142H atoms treated by a mixture of independent and constrained refinement
S = 0.98Δρmax = 0.14 e Å3
2650 reflectionsΔρmin = 0.18 e Å3
136 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.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
C10.67825 (18)0.10160 (10)0.43212 (9)0.0446 (4)
C20.7203 (2)0.04127 (10)0.49085 (10)0.0490 (4)
C30.6978 (2)0.06377 (13)0.57205 (11)0.0603 (5)
H30.725 (2)0.0233 (11)0.6117 (11)0.067 (5)*
C40.6343 (2)0.14221 (14)0.59470 (10)0.0618 (5)
C50.5926 (2)0.19971 (14)0.53433 (11)0.0607 (5)
H50.553 (2)0.2542 (12)0.5478 (9)0.059 (5)*
C60.61392 (19)0.18130 (10)0.45211 (10)0.0508 (4)
N70.69934 (18)0.08020 (9)0.34776 (8)0.0565 (4)
H70.611 (2)0.0748 (11)0.3143 (12)0.073 (6)*
N80.85605 (17)0.08802 (9)0.31136 (9)0.0595 (4)
O90.86195 (16)0.07215 (11)0.23793 (8)0.0891 (5)
O100.98268 (15)0.10748 (10)0.35257 (8)0.0845 (5)
C210.7865 (3)0.04470 (11)0.46764 (13)0.0698 (6)
H21A0.79710.07970.51680.127 (4)*
H21B0.90160.03940.44150.127 (4)*
H21C0.70400.07110.42950.127 (4)*
C410.6102 (3)0.16377 (18)0.68379 (12)0.1000 (8)
H41A0.63550.11400.71720.095 (6)*0.50
H41B0.48890.18190.69320.095 (6)*0.50
H41C0.69050.20950.69880.095 (6)*0.50
H41D0.57450.22290.68890.095 (6)*0.50
H41E0.72110.15500.71290.095 (6)*0.50
H41F0.51950.12740.70740.095 (6)*0.50
C610.5704 (3)0.24532 (12)0.38785 (12)0.0807 (6)
H61A0.51940.29540.41370.127 (4)*
H61B0.48570.22120.34930.127 (4)*
H61C0.67750.26120.35850.127 (4)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0354 (8)0.0583 (10)0.0402 (9)0.0026 (7)0.0000 (6)0.0054 (7)
C20.0343 (8)0.0576 (11)0.0552 (10)0.0065 (7)0.0022 (7)0.0009 (8)
C30.0508 (10)0.0809 (14)0.0491 (11)0.0075 (9)0.0024 (8)0.0138 (10)
C40.0515 (10)0.0894 (14)0.0445 (10)0.0074 (10)0.0042 (8)0.0082 (10)
C50.0560 (11)0.0638 (12)0.0624 (12)0.0011 (9)0.0065 (9)0.0152 (10)
C60.0457 (9)0.0564 (10)0.0502 (10)0.0005 (8)0.0014 (7)0.0026 (8)
N70.0376 (8)0.0881 (11)0.0439 (8)0.0028 (7)0.0006 (6)0.0136 (7)
N80.0469 (8)0.0810 (11)0.0505 (9)0.0012 (7)0.0062 (7)0.0103 (8)
O90.0657 (9)0.1543 (15)0.0472 (8)0.0058 (8)0.0115 (6)0.0240 (8)
O100.0451 (7)0.1375 (13)0.0711 (9)0.0194 (7)0.0026 (6)0.0200 (8)
C210.0573 (11)0.0564 (12)0.0957 (16)0.0020 (9)0.0062 (10)0.0003 (10)
C410.0969 (17)0.150 (2)0.0530 (13)0.0057 (15)0.0090 (11)0.0188 (14)
C610.0932 (14)0.0716 (13)0.0774 (14)0.0143 (11)0.0004 (12)0.0141 (11)
Geometric parameters (Å, º) top
C1—C21.393 (2)N8—O101.2173 (16)
C1—C61.394 (2)N8—O91.2290 (17)
C1—N71.4310 (19)C21—H21A0.9800
C2—C31.387 (2)C21—H21B0.9800
C2—C211.502 (2)C21—H21C0.9800
C3—C41.385 (3)C41—H41A0.9800
C3—H30.937 (17)C41—H41B0.9800
C4—C51.381 (3)C41—H41C0.9800
C4—C411.509 (3)C41—H41D0.9800
C5—C61.387 (2)C41—H41E0.9800
C5—H50.941 (18)C41—H41F0.9800
C6—C611.499 (2)C61—H61A0.9800
N7—N81.3405 (17)C61—H61B0.9800
N7—H70.874 (18)C61—H61C0.9800
C2—C1—C6122.75 (14)H21B—C21—H21C109.5
C2—C1—N7118.50 (14)C4—C41—H41A109.5
C6—C1—N7118.74 (14)C4—C41—H41B109.5
C3—C2—C1117.15 (16)H41A—C41—H41B109.5
C3—C2—C21121.15 (17)C4—C41—H41C109.5
C1—C2—C21121.71 (15)H41A—C41—H41C109.5
C4—C3—C2122.05 (17)H41B—C41—H41C109.5
C4—C3—H3120.5 (11)C4—C41—H41D109.5
C2—C3—H3117.5 (11)H41A—C41—H41D141.1
C5—C4—C3118.77 (16)H41B—C41—H41D56.3
C5—C4—C41120.9 (2)H41C—C41—H41D56.3
C3—C4—C41120.31 (19)C4—C41—H41E109.5
C4—C5—C6121.91 (18)H41A—C41—H41E56.3
C4—C5—H5120.8 (9)H41B—C41—H41E141.1
C6—C5—H5117.2 (9)H41C—C41—H41E56.3
C5—C6—C1117.36 (15)H41D—C41—H41E109.5
C5—C6—C61120.85 (16)C4—C41—H41F109.5
C1—C6—C61121.79 (15)H41A—C41—H41F56.3
N8—N7—C1120.47 (13)H41B—C41—H41F56.3
N8—N7—H7114.7 (12)H41C—C41—H41F141.1
C1—N7—H7122.8 (12)H41D—C41—H41F109.5
O10—N8—O9124.40 (14)H41E—C41—H41F109.5
O10—N8—N7118.92 (14)C6—C61—H61A109.5
O9—N8—N7116.64 (14)C6—C61—H61B109.5
C2—C21—H21A109.5H61A—C61—H61B109.5
C2—C21—H21B109.5C6—C61—H61C109.5
H21A—C21—H21B109.5H61A—C61—H61C109.5
C2—C21—H21C109.5H61B—C61—H61C109.5
H21A—C21—H21C109.5
C6—C1—C2—C30.8 (2)C4—C5—C6—C10.5 (2)
N7—C1—C2—C3179.74 (13)C4—C5—C6—C61179.05 (17)
C6—C1—C2—C21178.93 (15)C2—C1—C6—C50.2 (2)
N7—C1—C2—C210.0 (2)N7—C1—C6—C5179.12 (13)
C1—C2—C3—C40.8 (2)C2—C1—C6—C61179.72 (15)
C21—C2—C3—C4178.95 (16)N7—C1—C6—C611.4 (2)
C2—C3—C4—C50.2 (3)C2—C1—N7—N884.18 (19)
C2—C3—C4—C41179.43 (16)C6—C1—N7—N896.85 (18)
C3—C4—C5—C60.5 (3)C1—N7—N8—O105.5 (2)
C41—C4—C5—C6179.91 (16)C1—N7—N8—O9176.74 (15)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N7—H7···O9i0.874 (18)2.080 (19)2.9320 (18)164.6 (17)
Symmetry code: (i) x1/2, y, z+1/2.

Experimental details

Crystal data
Chemical formulaC9H12N2O2
Mr180.21
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)295
a, b, c (Å)7.6217 (6), 15.8538 (13), 16.3696 (12)
V3)1978.0 (3)
Z8
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.30 × 0.25 × 0.15
Data collection
DiffractometerOxford Diffraction Xcalibur
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
14835, 2650, 1329
Rint0.038
(sin θ/λ)max1)0.694
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.046, 0.142, 0.98
No. of reflections2650
No. of parameters136
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.14, 0.18

Computer programs: CrysAlis CCD (Oxford Diffraction, 2002 ??2006), CrysAlis RED (Oxford Diffraction, 2002 ??2006), CrysAlis RED, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL (Sheldrick, 1990), SHELXL97.

Selected geometric parameters (Å, º) top
C1—C21.393 (2)C5—C61.387 (2)
C1—C61.394 (2)N7—N81.3405 (17)
C1—N71.4310 (19)N7—H70.874 (18)
C2—C31.387 (2)N8—O101.2173 (16)
C3—C41.385 (3)N8—O91.2290 (17)
C4—C51.381 (3)
C2—C1—C6122.75 (14)N8—N7—C1120.47 (13)
C3—C2—C1117.15 (16)N8—N7—H7114.7 (12)
C4—C3—C2122.05 (17)C1—N7—H7122.8 (12)
C5—C4—C3118.77 (16)O10—N8—O9124.40 (14)
C4—C5—C6121.91 (18)O10—N8—N7118.92 (14)
C5—C6—C1117.36 (15)O9—N8—N7116.64 (14)
C2—C1—N7—N884.18 (19)C1—N7—N8—O105.5 (2)
C6—C1—N7—N896.85 (18)C1—N7—N8—O9176.74 (15)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N7—H7···O9i0.874 (18)2.080 (19)2.9320 (18)164.6 (17)
Symmetry code: (i) x1/2, y, z+1/2.
 

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