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Low-temperature redetermination of benzofurazan 1-oxide

aDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
*Correspondence e-mail: seikweng@um.edu.my

(Received 3 May 2009; accepted 6 May 2009; online 14 May 2009)

In the six-membered ring of the low-temperature crystal structure of benzofurazan 1-oxide, C6H4N2O2, the two C atoms adjacent to the N atoms are linked by a delocalized aromatic bond [1.402 (2) Å]; each is connected to its neighbour by a longer, more localized, bond [1.420 (2), 1.430 (2) Å]. However, the next two bonds in the ring approximate double bonds [1.357 (2), 1.366 (2) Å]. As such, the six-membered ring is better described as a cyclo­hexa­diene system, in contrast to the description in the room-temperature structure reported by Britton & Olson (1979[Britton, D. & Olson, J. M. (1979). Acta Cryst. B35, 3076-3078.]) [Acta Cryst. B35, 3076–3078].

Related literature

For the room-temperature structure in the P[\overline{1}] setting [6.772 (3), 7.515 (4), 7.759 (4) Å, 99.08 (3), 114.94 (3), 112.67 (3) °], see: Britton & Olson (1979[Britton, D. & Olson, J. M. (1979). Acta Cryst. B35, 3076-3078.]). For the geometry-optimized structure, see: Friedrichsen, 1995[Friedrichsen, W. (1995). J. Mol. Struct. (Theochem), 342, 23-31.]; Ponder et al. (1994[Ponder, M., Fowler, J. E. & Schaeffer, H. F. (1994). J. Org. Chem. 59, 6431-6436.]); Rauhut (1996[Rauhut, G. (1996). J. Comput. Chem. 17, 1848-1856.]). For details of the synthesis, see: Terrian et al. (1992[Terrian, D. L., Houghtaling, M. A. & Ames, J. R. (1992). J Chem. Educ. 69, 589-590.]); Wolthius (1979[Wolthius, E. (1979). J. Chem. Educ. 56, 343-344.]). For work mentioning the original structure, see: Ammon & Bhattacharjee (1982[Ammon, H. L. & Bhattacharjee, S. K. (1982). Acta Cryst. B38, 2498-2502.]); Bird (1993[Bird, C. W. (1993). Tetrahedron, 49, 8441-8448.]); Cerecetto & González (2007[Cerecetto, H. & González, M. (2007). Topics Heterocycl. Chem. 10, 265-308.]); Ojala et al. (1999[Ojala, C. R., Ojala, W. H., Britton, D. & Gougoutas, J. Z. (1999). Acta Cryst. B55, 530-542.]); Ramm et al. (1991[Ramm, M., Schultz, B., Rudert, R., Göhrmann, B. & Niclas, H.-J. (1991). Acta Cryst. C47, 1700-1702.]).

[Scheme 1]

Experimental

Crystal data
  • C6H4N2O2

  • Mr = 136.11

  • Triclinic, [P \overline 1]

  • a = 6.6751 (2) Å

  • b = 7.3256 (2) Å

  • c = 7.6842 (2) Å

  • α = 100.710 (2)°

  • β = 114.265 (2)°

  • γ = 111.747 (2)°

  • V = 291.71 (1) Å3

  • Z = 2

  • Mo Kα radiation

  • μ = 0.12 mm−1

  • T = 100 K

  • 0.30 × 0.25 × 0.10 mm

Data collection
  • Bruker SMART APEX diffractometer

  • Absorption correction: none

  • 1952 measured reflections

  • 1276 independent reflections

  • 1110 reflections with I > 2σ(I)

  • Rint = 0.012

Refinement
  • R[F2 > 2σ(F2)] = 0.035

  • wR(F2) = 0.110

  • S = 1.03

  • 1276 reflections

  • 108 parameters

  • 4 restraints

  • All H-atom parameters refined

  • Δρmax = 0.33 e Å−3

  • Δρmin = −0.21 e Å−3

Table 1
Selected bond lengths (Å)

O1—N1 1.230 (1)
O2—N2 1.381 (1)
O2—N1 1.443 (2)
N1—C6 1.336 (2)
N2—C1 1.327 (2)
C1—C6 1.409 (2)
C1—C2 1.430 (2)
C2—C3 1.357 (2)
C3—C4 1.436 (2)
C4—C5 1.366 (2)
C5—C6 1.420 (2)

Data collection: APEX2 (Bruker, 2008[Bruker (2008). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2008[Bruker (2008). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: X-SEED (Barbour, 2001[Barbour, L. J. (2001). J. Supramol. Chem. 1, 189-191.]); software used to prepare material for publication: publCIF (Westrip, 2009[Westrip, S. P. (2009). publCIF. In preparation.]).

Supporting information


Comment top

Researchers have used the published structure of benzofurazan 1-oxide (Britton & Olson, 1979) in, for example, studies on packing (Ammon & Bhattacharjee, 1982; Ojala et al., 1999; Ramm et al., 1991), influence of N-oxide formation on heteroaromaticity (Bird, 1993), and reactivity and biology (Cerecetto & González, 2007). Bond dimensions from geometry-optimization calculations (Friedrichsen, 1995; Ponder et al.,1994; Rauhut, 1996) have also been compared with values taken from the solid-state structure.

The present low-temperature structure (Fig. 1 & Table 1) reveals features quite distinct from those disclosed in the original, room-temperature, analysis (Britton & Olson, 1979). In the six-membered ring, the two carbon atoms adjacent to the nitrogen atoms are linked by a delocalized aromatic bond [1.402 (2) Å]; each is connected to its neighbor by a longer, more localized, bond [1.420 (2), 1.430 (2) Å]. However, the next two bonds in the ring approximate double-bonds [1.357 (2), 1.366 (2) Å]. As such, the six-membered ring is better described as a cyclohexadiene system.

Related literature top

For the room-temperature structure in the P1 setting [6.772 (3), 7.515 (4), 7.759 (4) Å, 99.08 (3), 114.94 (3), 112.67 (3) °], see: Britton & Olson (1979). For the geometry-optimized structure, see: Friedrichsen, 1995; Ponder et al. (1994); Rauhut (1996). For details of the synthesis, see: Terrian et al. (1992); Wolthius (1979). For work mentioning the original structure, see: Ammon & Bhattacharjee (1982); Bird (1993); Cerecetto & González (2007); Ojala et al. (1999); Ramm et al. (1991).

Experimental top

The compound was synthesized according to a reported procedure (Terrian et al., 1992; Wolthius, 1979). Crystals were grown with THF as solvent.

Refinement top

The carbon-bound H-atoms were restrained to C—H 0.95±0.01 Å; their temperature factors were freely refined.

Computing details top

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: publCIF (Westrip, 2009).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound. Displacement ellipsoids are drawn at the 70% probability level, and hydrogen atoms are drawn as spheres of arbitrary radius.
(I) top
Crystal data top
C6H4N2O2Z = 2
Mr = 136.11F(000) = 140
Triclinic, P1Dx = 1.550 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 6.6751 (2) ÅCell parameters from 1320 reflections
b = 7.3256 (2) Åθ = 3.2–28.3°
c = 7.6842 (2) ŵ = 0.12 mm1
α = 100.710 (2)°T = 100 K
β = 114.265 (2)°Irregular block, yellow-orange
γ = 111.747 (2)°0.30 × 0.25 × 0.10 mm
V = 291.71 (1) Å3
Data collection top
Bruker SMART APEX
diffractometer
1110 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.012
Graphite monochromatorθmax = 27.5°, θmin = 3.2°
ω scansh = 78
1952 measured reflectionsk = 99
1276 independent reflectionsl = 99
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)] = 0.035All H-atom parameters refined
wR(F2) = 0.110 w = 1/[σ2(Fo2) + (0.0685P)2 + 0.0855P]
where P = (Fo2 + 2Fc2)/3
S = 1.03(Δ/σ)max = 0.001
1276 reflectionsΔρmax = 0.33 e Å3
108 parametersΔρmin = 0.21 e Å3
4 restraintsExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.03 (1)
Crystal data top
C6H4N2O2γ = 111.747 (2)°
Mr = 136.11V = 291.71 (1) Å3
Triclinic, P1Z = 2
a = 6.6751 (2) ÅMo Kα radiation
b = 7.3256 (2) ŵ = 0.12 mm1
c = 7.6842 (2) ÅT = 100 K
α = 100.710 (2)°0.30 × 0.25 × 0.10 mm
β = 114.265 (2)°
Data collection top
Bruker SMART APEX
diffractometer
1110 reflections with I > 2σ(I)
1952 measured reflectionsRint = 0.012
1276 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0354 restraints
wR(F2) = 0.110All H-atom parameters refined
S = 1.03Δρmax = 0.33 e Å3
1276 reflectionsΔρmin = 0.21 e Å3
108 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.1183 (2)0.2141 (2)0.0082 (1)0.0274 (3)
O20.5178 (2)0.2611 (2)0.1146 (1)0.0271 (3)
N10.3061 (2)0.2329 (2)0.1385 (2)0.0211 (3)
N20.7112 (2)0.2839 (2)0.2955 (2)0.0257 (3)
C10.6232 (2)0.2701 (2)0.4219 (2)0.0188 (3)
C20.7496 (3)0.2863 (2)0.6308 (2)0.0202 (3)
C30.6182 (3)0.2669 (2)0.7284 (2)0.0207 (3)
C40.3643 (3)0.2321 (2)0.6312 (2)0.0209 (3)
C50.2382 (3)0.2174 (2)0.4325 (2)0.0199 (3)
C60.3750 (2)0.2377 (2)0.3296 (2)0.0181 (3)
H20.919 (2)0.310 (3)0.693 (3)0.030 (4)*
H30.701 (3)0.278 (3)0.867 (2)0.037 (5)*
H40.281 (3)0.221 (3)0.706 (2)0.027 (4)*
H50.072 (2)0.197 (3)0.369 (2)0.031 (4)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0242 (5)0.0333 (6)0.0172 (5)0.0139 (4)0.0039 (4)0.0130 (4)
O20.0270 (6)0.0398 (6)0.0190 (5)0.0172 (5)0.0137 (4)0.0157 (4)
N10.0213 (6)0.0237 (6)0.0158 (5)0.0105 (5)0.0077 (5)0.0098 (4)
N20.0237 (6)0.0361 (7)0.0202 (6)0.0155 (5)0.0120 (5)0.0144 (5)
C10.0198 (6)0.0199 (6)0.0171 (6)0.0096 (5)0.0095 (5)0.0090 (5)
C20.0187 (6)0.0231 (6)0.0175 (6)0.0109 (5)0.0072 (5)0.0103 (5)
C30.0240 (7)0.0215 (6)0.0147 (6)0.0109 (5)0.0083 (5)0.0093 (5)
C40.0246 (7)0.0228 (6)0.0192 (6)0.0120 (5)0.0137 (6)0.0102 (5)
C50.0188 (6)0.0213 (6)0.0200 (6)0.0104 (5)0.0096 (5)0.0096 (5)
C60.0200 (6)0.0175 (6)0.0136 (5)0.0086 (5)0.0066 (5)0.0073 (4)
Geometric parameters (Å, º) top
O1—N11.230 (1)C3—C41.436 (2)
O2—N21.381 (1)C4—C51.366 (2)
O2—N11.443 (2)C5—C61.420 (2)
N1—C61.336 (2)C2—H20.956 (9)
N2—C11.327 (2)C3—H30.948 (9)
C1—C61.409 (2)C4—H40.946 (9)
C1—C21.430 (2)C5—H50.947 (9)
C2—C31.357 (2)
N2—O2—N1109.4 (1)N1—C6—C1106.9 (1)
O1—N1—C6136.0 (1)N1—C6—C5129.7 (1)
O1—N1—O2117.7 (1)C1—C6—C5123.5 (1)
C6—N1—O2106.3 (1)C3—C2—H2124 (1)
C1—N2—O2105.0 (1)C1—C2—H2119 (1)
N2—C1—C6112.5 (1)C2—C3—H3117 (1)
N2—C1—C2128.0 (1)C4—C3—H3120 (1)
C6—C1—C2119.5 (1)C5—C4—H4118 (1)
C3—C2—C1116.8 (1)C3—C4—H4120 (1)
C2—C3—C4122.9 (1)C4—C5—H5122 (1)
C5—C4—C3121.9 (1)C6—C5—H5122 (1)
C4—C5—C6115.4 (1)
N2—O2—N1—O1178.7 (1)O1—N1—C6—C1178.3 (1)
N2—O2—N1—C60.4 (1)O2—N1—C6—C10.6 (1)
N1—O2—N2—C10.1 (1)O1—N1—C6—C51.2 (2)
O2—N2—C1—C60.3 (2)O2—N1—C6—C5179.9 (1)
O2—N2—C1—C2179.1 (1)N2—C1—C6—N10.5 (2)
N2—C1—C2—C3179.9 (1)C2—C1—C6—N1178.9 (1)
C6—C1—C2—C30.6 (2)N2—C1—C6—C5179.9 (1)
C1—C2—C3—C40.1 (2)C2—C1—C6—C50.7 (2)
C2—C3—C4—C50.4 (2)C4—C5—C6—N1179.2 (1)
C3—C4—C5—C60.3 (2)C4—C5—C6—C10.2 (2)

Experimental details

Crystal data
Chemical formulaC6H4N2O2
Mr136.11
Crystal system, space groupTriclinic, P1
Temperature (K)100
a, b, c (Å)6.6751 (2), 7.3256 (2), 7.6842 (2)
α, β, γ (°)100.710 (2), 114.265 (2), 111.747 (2)
V3)291.71 (1)
Z2
Radiation typeMo Kα
µ (mm1)0.12
Crystal size (mm)0.30 × 0.25 × 0.10
Data collection
DiffractometerBruker SMART APEX
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
1952, 1276, 1110
Rint0.012
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.035, 0.110, 1.03
No. of reflections1276
No. of parameters108
No. of restraints4
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.33, 0.21

Computer programs: APEX2 (Bruker, 2008), SAINT (Bruker, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), X-SEED (Barbour, 2001), publCIF (Westrip, 2009).

Selected bond lengths (Å) top
O1—N11.230 (1)C1—C21.430 (2)
O2—N21.381 (1)C2—C31.357 (2)
O2—N11.443 (2)C3—C41.436 (2)
N1—C61.336 (2)C4—C51.366 (2)
N2—C11.327 (2)C5—C61.420 (2)
C1—C61.409 (2)
 

Acknowledgements

I thank the University of Malaya for supporting this study.

References

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