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In the title compound, C8H8N2O2, the nitr­amino group is planar and only slightly twisted with respect to the indoline rings. The bridgehead N—C bond is slightly shorter than in typical secondary aromatic nitr­amines. The N—N bond has some double-bond character. The mol­ecules are connected by weak C—H...O hydrogen bonds, forming chains parallel to the z direction.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100019144/gd1117sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270100019144/gd1117Isup2.hkl
Contains datablock I

CCDC reference: 162577

Comment top

Our studies on the molecular structure of secondary aromatic nitramines led to two conclusions. In molecular structures of typical secondary aromatic nitramines, there are two planare π-electron fragments, the aromatic ring and the nitramino (NNO2) group. These are not coplanar, and the π-electron system of the nitramino group is not conjugated with the ring as indicated by a large torsion angle about the Ar—N bond. The conformation of the nitramino group is determined by the four-cluster π-orbital system. The formally unshared electron pair on the amide nitrogen is shifted towards the electron deficient nitrogen of the N–nitro group. The interaction of the N–methylnitramino group with the aromatic ring is of inductive character even in the molecules containing positively charged ring as in 4–(N–methylnitramino)–1–methylpyridinium bromide (Zaleski et al., 1999a) and 4–(N–methylnitramino)–pyridine 1–oxide (Zaleski et al., 1999b). The twisted conformation of N-methyl-N-phenylnitramines (Ejsmont et al., 1998; Anulewicz et al., 1993) may result from the intermolecular interactions in the crystal network or from the sterical effects involving repulsion between oxygen atoms of the nitro groups and H atoms in the ortho positions. To resolve this problem, we have prepared a model compound viz. 1-nitroindoline, (I). \sch

It has been assumed that the five-membered ring constrains coplanarity of both π–electron systems. Conjugation between them should divert the charge distribution within the NNO2 group and give rise to some observable changes in its geometry and in spectral and chemical properties of the nitramine (I). The nitramino group in 1-nitroindoline (Fig. 1) is almost coplaner with the C1 and C8. The N7–C1 bond [1.406 (1) Å] is slightly shorter than in typical secondary aromatic nitramines, where it always exceeds 1.42 Å. The N7–C8 bond [1.462 (2) Å] is longer than in analogous non-cyclic nitramines (usually 1.44–1.45 Å). The C1–N7–C8 valence angle [113.0 (1)°] is a compromise between the value characteristic of trigonal hybridization and the internal angle in a regular pentagon. The N–N and N–O bonds have typical lengths; on the other hand, comparison of the FTIR spectra of (I) and its open chain analogues (N–alkyl–N–phenylnitramines) suggests some differences in the geometry of the nitramino group since the characteristic bands are shifted. The asymmetric stretch gives a strong band at 1505 cm-1 (typical 1520–1525 cm-1), symmetric stretching vibration at 1345 cm-1 is also out of usually observed region of 1280–1300 cm-1 (Daszkiewicz et al., 1995). The absorption bands may be shifted due to the steric interaction of the O11 and H6 which are very close to each other. Enlargement of some valence angles centred on C1, N7 and N10 [131.3 (1), 126.6 (1) and 118.4 (1)°, respectively] separates these atoms for the acceptable distance [C6···O11 2.849 (1) Å, H6···O11 2.31 Å]. It might have been enhanced more effectively by the twist along the N7–N10 bond but this is not what is observed. The torsion angle C1–N7–N10–O11 amounts to only 10.4 (2)° only and cannot seriously perturb the π–orbital system within the nitramino group. Consequently, the N–N bond [1.335 (2) Å] has some properties of the double bond, in spite of that it is longer than such a bond in e.g. azobenzene (Harada et al., 1997).

The five-membered ring is not planar, the geminal protons are in a different environment and their signals in the proton NMR spectrum are not isochronous, consequently two unresolvable multiplets are observed. Considering that the sum of the internal valence angles is nearly exactly 540° we may assume, for the first sight, that the ring is planar. However, the torsion angles N7–C8–C9–C2 and C1–N7–C8–C9 are ca 7.0 (1)°, and suffice to make the aliphatic protons magnetically non-equivalent. It is worth noting that the chemical shift of N-methylene group is nearly the same as observed in the spectrum of N-ethyl-N-phenylnitramine.

The molecules of (I) are aranged in the XZ plane. They are connected to each other by weak C3—H3···O12i hydrogen bonds forming chains parallel to the Z direction (Fig. 2).

Related literature top

For related literature, see: Anulewicz et al. (1993); Daszkiewicz et al. (1995); Ejsmont et al. (1998); Harada et al. (1997); Zaleski et al. (1999a, 1999b).

Experimental top

Compound (I): Indoline (3.58 g, 0.03 mol) and sodium hydride (3.00 g of 60% NaH, 0.075 mol) were heated in boiling toluene for 2 h under nitrogen atmosphere. The mixture was cooled to room temperature, n-butyl nitrate (5.30 g, 0.045 mol) was added and the suspension was stirred for 1 h at 298 K. Water (20 ml) was added, the layers were separated and the toluene layer was extracted (3 x 20 ml) with aqueous 10% sodium hydrogen sulfate to remove unreacted amine. The solution was dried over anhydrous magnesium sulfate and evaporated in vacuum at 313 K. The residue (3.31 g, 67%) was crystallized from the ethyl ether–n–hexane yielding colourless crystals melting at 363–366 K. Recrystallization from methylene chloride–n–hexane gave 1-nitroindoline (1.30 g, 26%), m.p. 362.5–363.5 K. Crystals suitable for X-ray diffraction studies were obtained by slow evaporation of a methylene chloride solution at room temperature; the compound is light sensitive.

IR (KBr, cm-1): 1505, 1345 (N-nitro group stretching vibrations). 1H NMR (DMSO-d6, p.p.m.): 7.90, dd 3J = 8.0 Hz, 4J = 0.9 Hz, 1H (proton in ortho position); 7.11–7.39, m, 3H (remaining aromatic protons); 4.32–4.48, m, 4H and 3.11–3.31, m, 4H (aliphatic protons).

Refinement top

All H-atom parameters were refined: C—H distances ranged from 0.924 (18) to 0.994 (19) Å.

Computing details top

Cell refinement: KUMA Diffraction Software (KUMA, 1997); data reduction: KUMA Diffraction Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); 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. Molecular structure of (I) showing 50% probability displacement ellipsoids.
[Figure 2] Fig. 2. The packing diagram of (I) showing the hydrogen-bonding scheme. Displacement ellipsoids are drawn at the 50% probability level.
(I) top
Crystal data top
C8H8N2O2Z = 2
Mr = 164.16F(000) = 172
Triclinic, P1Dx = 1.450 Mg m3
a = 5.886 (2) ÅMo Kα radiation, λ = 0.71073 Å
b = 8.402 (3) ÅCell parameters from 19 reflections
c = 8.923 (3) Åθ = 15–26°
α = 116.80 (3)°µ = 0.11 mm1
β = 104.04 (3)°T = 293 K
γ = 92.53 (3)°Plates, colourless
V = 376.1 (2) Å30.6 × 0.5 × 0.25 mm
Data collection top
KUMA KM4
diffractometer
Rint = 0.006
Radiation source: fine-focus sealed tubeθmax = 30.1°, θmin = 2.7°
Graphite monochromatorh = 88
ω scansk = 108
2196 measured reflectionsl = 1012
2063 independent reflections2 standard reflections every 50 reflections
1643 reflections with I > 2σ(I) intensity decay: 4.1%
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.037All H-atom parameters refined
wR(F2) = 0.110Calculated w = 1/[σ2(Fo2) + (0.0555P)2 + 0.0575P]
where P = (Fo2 + 2Fc2)/3
S = 1.01(Δ/σ)max = 0.010
2063 reflectionsΔρmax = 0.25 e Å3
142 parametersΔρmin = 0.17 e Å3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.042 (10)
Crystal data top
C8H8N2O2γ = 92.53 (3)°
Mr = 164.16V = 376.1 (2) Å3
Triclinic, P1Z = 2
a = 5.886 (2) ÅMo Kα radiation
b = 8.402 (3) ŵ = 0.11 mm1
c = 8.923 (3) ÅT = 293 K
α = 116.80 (3)°0.6 × 0.5 × 0.25 mm
β = 104.04 (3)°
Data collection top
KUMA KM4
diffractometer
Rint = 0.006
2196 measured reflections2 standard reflections every 50 reflections
2063 independent reflections intensity decay: 4.1%
1643 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0370 restraints
wR(F2) = 0.110All H-atom parameters refined
S = 1.01Δρmax = 0.25 e Å3
2063 reflectionsΔρmin = 0.17 e Å3
142 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*/Ueq
C10.03253 (18)0.76359 (13)0.46292 (13)0.0372 (2)
C20.12229 (18)0.70046 (14)0.52725 (13)0.0382 (2)
C30.0669 (2)0.75623 (19)0.70445 (15)0.0511 (3)
C40.1423 (3)0.8750 (2)0.81636 (16)0.0586 (3)
C50.2939 (2)0.93635 (18)0.75082 (17)0.0564 (3)
C60.2431 (2)0.88204 (16)0.57318 (17)0.0494 (3)
N70.06979 (17)0.68569 (14)0.28014 (12)0.0463 (2)
C80.3063 (2)0.57703 (19)0.21843 (15)0.0490 (3)
C90.3355 (2)0.57295 (17)0.38166 (15)0.0458 (3)
O110.21270 (19)0.81134 (16)0.22450 (14)0.0695 (3)
O120.1192 (2)0.65732 (15)0.01832 (12)0.0685 (3)
N100.0130 (2)0.72110 (15)0.16956 (13)0.0514 (3)
H30.175 (3)0.716 (2)0.753 (2)0.082 (5)*
H40.185 (3)0.911 (3)0.936 (3)0.088 (6)*
H50.439 (3)1.016 (2)0.823 (2)0.067 (4)*
H60.342 (3)0.920 (2)0.525 (2)0.065 (4)*
H9A0.484 (3)0.614 (2)0.401 (2)0.066 (4)*
H8A0.414 (3)0.642 (2)0.181 (2)0.063 (4)*
H9B0.338 (3)0.448 (2)0.366 (2)0.062 (4)*
H8B0.304 (3)0.458 (2)0.126 (2)0.071 (5)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0391 (5)0.0382 (5)0.0365 (5)0.0059 (4)0.0108 (4)0.0199 (4)
C20.0392 (5)0.0419 (5)0.0365 (5)0.0063 (4)0.0115 (4)0.0211 (4)
C30.0562 (7)0.0624 (7)0.0393 (6)0.0082 (5)0.0157 (5)0.0276 (5)
C40.0661 (8)0.0635 (8)0.0348 (6)0.0095 (6)0.0053 (5)0.0189 (5)
C50.0521 (7)0.0481 (6)0.0487 (7)0.0018 (5)0.0026 (5)0.0158 (5)
C60.0446 (6)0.0461 (6)0.0551 (7)0.0021 (5)0.0104 (5)0.0252 (5)
N70.0487 (5)0.0566 (6)0.0360 (5)0.0001 (4)0.0124 (4)0.0248 (4)
C80.0462 (6)0.0561 (7)0.0384 (5)0.0002 (5)0.0041 (4)0.0222 (5)
C90.0393 (5)0.0525 (6)0.0448 (6)0.0001 (4)0.0102 (4)0.0242 (5)
O110.0711 (6)0.0838 (7)0.0789 (7)0.0095 (5)0.0390 (5)0.0518 (6)
O120.1010 (8)0.0766 (7)0.0429 (5)0.0260 (6)0.0270 (5)0.0373 (5)
N100.0677 (7)0.0572 (6)0.0478 (5)0.0199 (5)0.0291 (5)0.0337 (5)
Geometric parameters (Å, º) top
C1—C61.383 (2)O11—N101.226 (2)
C1—C21.388 (1)O12—N101.231 (2)
C1—N71.406 (1)C3—H30.98 (2)
C2—C31.376 (2)C4—H40.93 (2)
C2—C91.499 (2)C5—H50.94 (2)
C3—C41.381 (2)C6—H60.92 (2)
C4—C51.374 (2)C8—H8A0.95 (2)
C5—C61.384 (2)C8—H8B0.97 (2)
N7—N101.336 (1)C9—H9A0.98 (2)
N7—C81.462 (2)C9—H9B0.99 (2)
C8—C91.523 (2)
C6—C1—C2121.4 (1)C2—C3—H3121 (1)
C6—C1—N7131.3 (1)C4—C3—H3119 (1)
C2—C1—N7107.2 (1)C3—C4—H4121 (1)
C3—C2—C1119.8 (1)C5—C4—H4119 (1)
C3—C2—C9129.1 (1)C4—C5—H5123 (1)
C1—C2—C9111.1 (1)C6—C5—H5116 (1)
C2—C3—C4119.4 (1)C1—C6—H6119 (1)
C5—C4—C3120.1 (1)C5—C6—H6124 (1)
C4—C5—C6121.7 (1)N7—C8—H8A106 (1)
C1—C6—C5117.5 (1)C9—C8—H8A112 (1)
N10—N7—C1126.6 (1)N7—C8—H8B107 (1)
N10—N7—C8119.8 (1)C9—C8—H8B113 (1)
C1—N7—C8113.0 (1)H8A—C8—H8B114 (1)
N7—C8—C9103.5 (1)C2—C9—H9A112 (1)
C2—C9—C8104.7 (1)C8—C9—H9A109 (1)
O11—N10—O12125.2 (1)C2—C9—H9B111 (1)
O11—N10—N7118.4 (1)C8—C9—H9B110 (1)
O12—N10—N7116.4 (1)H9A—C9—H9B110 (1)
C6—C1—C2—C30.1 (2)C2—C1—N7—N10174.8 (1)
N7—C1—C2—C3179.7 (1)C6—C1—N7—C8175.6 (1)
C6—C1—C2—C9179.4 (1)C2—C1—N7—C84.0 (1)
N7—C1—C2—C90.9 (1)N10—N7—C8—C9178.4 (1)
C1—C2—C3—C40.2 (2)C1—N7—C8—C97.0 (1)
C9—C2—C3—C4179.6 (1)C3—C2—C9—C8175.5 (1)
C2—C3—C4—C50.2 (2)C1—C2—C9—C85.0 (1)
C3—C4—C5—C60.0 (2)N7—C8—C9—C26.9 (1)
C2—C1—C6—C50.3 (2)C1—N7—N10—O1110.4 (2)
N7—C1—C6—C5179.4 (1)C8—N7—N10—O11179.4 (1)
C4—C5—C6—C10.3 (2)C1—N7—N10—O12170.4 (1)
C6—C1—N7—N104.9 (2)C8—N7—N10—O120.3 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C3—H3···O12i0.98 (2)2.57 (2)3.335 (2)134 (1)
Symmetry code: (i) x, y, z+1.

Experimental details

Crystal data
Chemical formulaC8H8N2O2
Mr164.16
Crystal system, space groupTriclinic, P1
Temperature (K)293
a, b, c (Å)5.886 (2), 8.402 (3), 8.923 (3)
α, β, γ (°)116.80 (3), 104.04 (3), 92.53 (3)
V3)376.1 (2)
Z2
Radiation typeMo Kα
µ (mm1)0.11
Crystal size (mm)0.6 × 0.5 × 0.25
Data collection
DiffractometerKUMA KM4
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
2196, 2063, 1643
Rint0.006
(sin θ/λ)max1)0.705
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.037, 0.110, 1.01
No. of reflections2063
No. of parameters142
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.25, 0.17

Computer programs: KUMA Diffraction Software (KUMA, 1997), KUMA Diffraction Software, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), SHELXTL (Sheldrick, 1990), SHELXL97.

Selected geometric parameters (Å, º) top
C1—C61.383 (2)C5—C61.384 (2)
C1—C21.388 (1)N7—N101.336 (1)
C1—N71.406 (1)N7—C81.462 (2)
C2—C31.376 (2)C8—C91.523 (2)
C2—C91.499 (2)O11—N101.226 (2)
C3—C41.381 (2)O12—N101.231 (2)
C4—C51.374 (2)
C1—N7—C8—C97.0 (1)C1—N7—N10—O1110.4 (2)
C3—C2—C9—C8175.5 (1)C8—N7—N10—O11179.4 (1)
C1—C2—C9—C85.0 (1)C1—N7—N10—O12170.4 (1)
N7—C8—C9—C26.9 (1)C8—N7—N10—O120.3 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C3—H3···O12i0.98 (2)2.57 (2)3.335 (2)134 (1)
Symmetry code: (i) x, y, z+1.
 

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