supplementary materials


rz5053 scheme

Acta Cryst. (2013). E69, o667-o668    [ doi:10.1107/S1600536813008970 ]

2-(4-Methylphenyl)-6-nitro-1,3-benzoxazole

R. Centore, V. Piccialli and A. Tuzi

Abstract top

The title compound, C14H10N2O3, is a [pi]-conjugated molecule containing a benzoxazole aromatic fused heterobicycle. The benzoxazole ring system is planar within 0.01 Å. The molecule assumes an approximately flat conformation, the benzoxazole ring system forming dihedral angles of 6.52 (12) and 7.4 (3)° with the benzene ring and the nitro group, respectively. In the crystal, molecules are connected by very weak C-H...O hydrogen interactions, forming chains running parallel to the a or c axes. The methyl H atoms are disordered over two sets of sites of equal occupancy rotated by 60°.

Comment top

Heterocycles are important compounds of synthetic chemistry. Besides their long standing and relevant application as drugs and bioactive compounds, aromatic heterocycles are playing a fundamental role in modern material chemistry as building blocks of conjugated active molecules in some emerging fields of organic electronics and optoelectronics: conducting polymers and organic solar cells (Heeger, 2010), organic field-effect transistors (Centore, Ricciotti et al., 2012), nonlinear optically active and piezoelectric compounds (Dalton, 2002; Carella, Centore, Sirigu et al. (2004); Centore, Concilio et al., 2012). The chemical investigation is mainly directed to the synthesis of new molecules or conjugated polymers containing heterocyclic moieties. However, also the structural investigation of the molecules is relevant, pointing towards the quantitative evaluation of the structural parameters related to the conjugation (Carella, Centore, Fort et al., 2004; Gainsford et al., 2008; Capobianco et al., 2012; Capobianco et al., 2013). Following our interest in the synthesis and characterization of new heterocyclic compounds, including metal containing heterocyclic compounds (Takjoo et al., 2011; Takjoo & Centore, 2013) for applications as advanced materials and bioactive compounds, and in the analysis of crystal structures controlled by the formation of H bonds (Centore, Fusco, Jazbinsek et al., 2013), we report, in the present paper, the structural investigation of the title compound, shown in Scheme 1. 2-(4-methyl)-phenyl-6-nitro-benzoxazole is an organic dye containing the 6-nitrobenzoxazole acceptor group conjugated with a 4-methylphenyl moiety. The 6-nitrobenzoxazole-2-yl moiety has been used in the synthesis of polymers showing quadratic NLO behaviour (Bruno et al., 2002).

The molecular structure of the title compound is shown in Fig. 1. The phenyl and benzoxazole rings are nearly coplanar, the dihedral angle between the mean planes being 6.7 (1)°. That structural feature is in accordance with the expected π conjugation of the compound.

Molecules in the crystal form rows through very weak hydrogen interactions between methyl or aromatic C–H donors and oxygen acceptors of the nitro group (Fig. 2 and Fig. 3; Table 1). The chains, which have graph set symbol C11(14) and C11(7) are generated, respectively, by the b and a glide planes.

Related literature top

For general information on heterocycles in organic electronics and optoelectronics, see: Dalton (2002); Heeger (2010). For heterocycle-based semiconductors, optoelectronic and piezoelectric materials, see: Carella, Centore, Sirigu et al. (2004); Centore, Ricciotti et al. (2012); Centore, Concilio et al. (2012). For structural and theoretical analysis of conjugation in heterocycle-based organic molecules, see: Carella, Centore, Fort et al. (2004); Gainsford et al. (2008). For structural and theoretical analysis of conjugation in heterocycle-based metallorganic compounds, see: Takjoo et al. (2011); Takjoo & Centore (2013). For theoretical computations on similar compounds, see: Capobianco et al. (2012, 2013). For the synthesis of related heterocyclic compounds, see: Bruno et al. (2002); Centore et al. (2007); Piccialli et al. (2013); Centore, Fusco, Capobianco et al. (2013). For hydrogen bonding in crystals see: Desiraju & Steiner (1999); Centore, Fusco, Jazbinsek et al. (2013).

Experimental top

The title compound was prepared by reaction of 2-amino-5-nitrophenol (5.00 g, 32.4 mmol) with toluic acid (4.41 g, 32.4 mmol) in polyphosphoric acid (150 g) at 150°C. The dehydration procedure is analogous to that we have already described for the synthesis of similar chromophores (Bruno et al., 2002; Centore et al., 2007). Purification of the title compound was obtained by recrystallization from ethanol. The final yield was 5.69 g (69%). M. p. 437 K. Single crystals were obtained by slow evaporation of an ethanol solution. 1H-NMR (CDCl3) δ 2.47 (s, 3H), 7.38 (d, 2H, J = 7.9 Hz), 7.82 (d, 1H, J= 8.5 Hz), 8.18 (d, 2H, J = 8.3 Hz), 8.33 (d, 1H, J= 8.7 Hz), 8.48 (d, 1H, J= 1.8 Hz).

Refinement top

All H atoms were generated stereochemically. In particular, the methyl group is disordered over two sets of sites of equal occupancy rotated from each other by 60°. All H atoms were refined by a riding model with C—H = 0.93-0.96 Å and with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(C) for methyl hydrogen atoms.

Computing details top

Data collection: MACH3/PC Software (Nonius, 1996); cell refinement: CELLFITW (Centore, 2004); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2006); software used to prepare material for publication: WinGX (Farrugia, 2012).

Figures top
[Figure 1] Fig. 1. ORTEP view of the molecular structure of the title compound. Thermal ellipsoids are drawn at 50% probability level. Only one orientation of the disordered methyl group is shown.
[Figure 2] Fig. 2. Row of molecules of the title compound running along the a axis. Only one orientation of the disordered methyl group is shown. Hydrogen bonds are shown as dashed lines.
[Figure 3] Fig. 3. Row of molecules of the title compound running along the c. Only one orientation of the disordered methyl group is shown. Hydrogen bonds are shown as dashed lines.
2-(4-Methylphenyl)-6-nitro-1,3-benzoxazole top
Crystal data top
C14H10N2O3F(000) = 1056
Mr = 254.24Dx = 1.388 Mg m3
Orthorhombic, PbcaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2abCell parameters from 25 reflections
a = 27.251 (4) Åθ = 12.2–12.4°
b = 7.4457 (6) ŵ = 0.10 mm1
c = 11.990 (9) ÅT = 293 K
V = 2432.8 (19) Å3Prism, brown
Z = 80.40 × 0.20 × 0.20 mm
Data collection top
Enraf–Nonius MACH3
diffractometer
Rint = 0.020
Radiation source: fine-focus sealed tubeθmax = 25.0°, θmin = 1.5°
Graphite monochromatorh = 1232
non–profiled ω scansk = 38
2968 measured reflectionsl = 514
2140 independent reflections1 standard reflections every 120 min
970 reflections with I > 2σ(I) intensity decay: none
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)] = 0.055Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.168H-atom parameters constrained
S = 1.11 w = 1/[σ2(Fo2) + (0.0553P)2 + 0.383P]
where P = (Fo2 + 2Fc2)/3
2140 reflections(Δ/σ)max < 0.001
174 parametersΔρmax = 0.14 e Å3
0 restraintsΔρmin = 0.19 e Å3
Crystal data top
C14H10N2O3V = 2432.8 (19) Å3
Mr = 254.24Z = 8
Orthorhombic, PbcaMo Kα radiation
a = 27.251 (4) ŵ = 0.10 mm1
b = 7.4457 (6) ÅT = 293 K
c = 11.990 (9) Å0.40 × 0.20 × 0.20 mm
Data collection top
Enraf–Nonius MACH3
diffractometer
Rint = 0.020
2968 measured reflectionsθmax = 25.0°
2140 independent reflections1 standard reflections every 120 min
970 reflections with I > 2σ(I) intensity decay: none
Refinement top
R[F2 > 2σ(F2)] = 0.055H-atom parameters constrained
wR(F2) = 0.168Δρmax = 0.14 e Å3
S = 1.11Δρmin = 0.19 e Å3
2140 reflectionsAbsolute structure: ?
174 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
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)
O10.05625 (9)0.1644 (3)0.0918 (2)0.0545 (7)
O20.25311 (13)0.0885 (6)0.2271 (3)0.1125 (14)
O30.19587 (12)0.0394 (6)0.3439 (3)0.1144 (14)
N10.08562 (12)0.1994 (4)0.0827 (3)0.0614 (10)
N20.21215 (15)0.0363 (6)0.2493 (4)0.0771 (11)
C10.14836 (14)0.4375 (6)0.1283 (4)0.0819 (15)
H1A0.16840.33290.13910.123*0.57 (5)
H1B0.14770.50680.19580.123*0.57 (5)
H1C0.16180.50900.06900.123*0.57 (5)
H1D0.15020.56630.13020.123*0.43 (5)
H1E0.17090.39230.07350.123*0.43 (5)
H1F0.15680.39010.20020.123*0.43 (5)
C20.09695 (16)0.3808 (5)0.0983 (4)0.0624 (12)
C30.05929 (17)0.3930 (6)0.1742 (4)0.0754 (13)
H30.06560.44110.24430.091*
C40.01233 (16)0.3358 (6)0.1496 (4)0.0710 (13)
H40.01220.34200.20350.085*
C50.00180 (14)0.2695 (5)0.0448 (3)0.0516 (10)
C60.03907 (14)0.2611 (5)0.0325 (3)0.0621 (11)
H60.03250.21820.10380.074*
C70.08606 (15)0.3154 (6)0.0058 (4)0.0682 (13)
H70.11070.30750.05920.082*
C80.04769 (15)0.2121 (5)0.0175 (3)0.0521 (10)
C90.12336 (14)0.1393 (5)0.0134 (3)0.0548 (11)
C100.17235 (15)0.1012 (6)0.0351 (4)0.0724 (13)
H100.18550.11460.10620.087*
C110.20086 (14)0.0426 (6)0.0532 (4)0.0718 (13)
H110.23370.01390.04160.086*
C120.18069 (14)0.0268 (6)0.1583 (4)0.0592 (11)
C130.13235 (14)0.0639 (5)0.1837 (3)0.0571 (11)
H130.11940.05250.25510.069*
C140.10530 (14)0.1191 (5)0.0941 (3)0.0509 (10)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0553 (17)0.0632 (18)0.0449 (16)0.0015 (13)0.0038 (13)0.0002 (14)
O20.057 (2)0.171 (4)0.110 (3)0.020 (2)0.005 (2)0.013 (3)
O30.086 (2)0.190 (4)0.068 (2)0.022 (3)0.004 (2)0.022 (3)
N10.064 (2)0.073 (3)0.0474 (19)0.0022 (18)0.010 (2)0.0039 (19)
N20.058 (2)0.096 (3)0.077 (3)0.006 (2)0.004 (2)0.006 (3)
C10.073 (3)0.070 (3)0.103 (4)0.010 (3)0.024 (3)0.008 (3)
C20.071 (3)0.051 (3)0.066 (3)0.000 (2)0.008 (3)0.011 (3)
C30.090 (3)0.087 (3)0.049 (3)0.014 (3)0.011 (3)0.007 (3)
C40.075 (3)0.086 (3)0.052 (3)0.009 (3)0.002 (2)0.001 (3)
C50.060 (2)0.051 (3)0.044 (2)0.000 (2)0.002 (2)0.003 (2)
C60.064 (3)0.073 (3)0.050 (2)0.004 (3)0.002 (2)0.004 (2)
C70.060 (3)0.078 (3)0.067 (3)0.006 (2)0.004 (2)0.001 (3)
C80.067 (3)0.051 (3)0.038 (2)0.000 (2)0.001 (2)0.003 (2)
C90.058 (3)0.058 (3)0.048 (2)0.009 (2)0.008 (2)0.007 (2)
C100.065 (3)0.093 (4)0.058 (3)0.003 (3)0.019 (3)0.001 (3)
C110.053 (3)0.092 (3)0.070 (3)0.001 (3)0.010 (2)0.003 (3)
C120.050 (2)0.066 (3)0.062 (3)0.003 (2)0.005 (2)0.002 (2)
C130.059 (3)0.060 (3)0.052 (3)0.004 (2)0.005 (2)0.001 (2)
C140.048 (2)0.051 (2)0.054 (3)0.005 (2)0.006 (2)0.005 (2)
Geometric parameters (Å, º) top
O1—C81.378 (4)C3—H30.9300
O1—C141.379 (4)C4—C51.380 (5)
O2—N21.212 (4)C4—H40.9300
O3—N21.218 (5)C5—C61.376 (5)
N1—C81.299 (4)C5—C81.452 (5)
N1—C91.396 (5)C6—C71.381 (5)
N2—C121.465 (5)C6—H60.9300
C1—C21.506 (5)C7—H70.9300
C1—H1A0.9600C9—C141.387 (5)
C1—H1B0.9600C9—C101.389 (5)
C1—H1C0.9600C10—C111.383 (6)
C1—H1D0.9600C10—H100.9300
C1—H1E0.9600C11—C121.380 (5)
C1—H1F0.9600C11—H110.9300
C2—C71.373 (6)C12—C131.380 (5)
C2—C31.375 (6)C13—C141.366 (5)
C3—C41.381 (6)C13—H130.9300
C8—O1—C14104.2 (3)C5—C4—H4120.1
C8—N1—C9104.6 (3)C3—C4—H4120.1
O2—N2—O3122.3 (4)C6—C5—C4118.4 (4)
O2—N2—C12118.5 (4)C6—C5—C8121.4 (4)
O3—N2—C12119.1 (4)C4—C5—C8120.2 (4)
C2—C1—H1A109.5C5—C6—C7121.0 (4)
C2—C1—H1B109.5C5—C6—H6119.5
H1A—C1—H1B109.5C7—C6—H6119.5
C2—C1—H1C109.5C2—C7—C6121.0 (4)
H1A—C1—H1C109.5C2—C7—H7119.5
H1B—C1—H1C109.5C6—C7—H7119.5
C2—C1—H1D109.5N1—C8—O1114.8 (3)
H1A—C1—H1D141.1N1—C8—C5128.7 (4)
H1B—C1—H1D56.3O1—C8—C5116.6 (3)
H1C—C1—H1D56.3C14—C9—C10119.5 (4)
C2—C1—H1E109.5C14—C9—N1109.0 (3)
H1A—C1—H1E56.3C10—C9—N1131.4 (4)
H1B—C1—H1E141.1C11—C10—C9117.4 (4)
H1C—C1—H1E56.3C11—C10—H10121.3
H1D—C1—H1E109.5C9—C10—H10121.3
C2—C1—H1F109.5C12—C11—C10120.1 (4)
H1A—C1—H1F56.3C12—C11—H11119.9
H1B—C1—H1F56.3C10—C11—H11119.9
H1C—C1—H1F141.1C13—C12—C11124.4 (4)
H1D—C1—H1F109.5C13—C12—N2117.3 (4)
H1E—C1—H1F109.5C11—C12—N2118.3 (4)
C7—C2—C3117.7 (4)C14—C13—C12113.7 (4)
C7—C2—C1121.1 (4)C14—C13—H13123.1
C3—C2—C1121.2 (4)C12—C13—H13123.1
C2—C3—C4122.0 (4)C13—C14—O1127.8 (4)
C2—C3—H3119.0C13—C14—C9124.8 (4)
C4—C3—H3119.0O1—C14—C9107.4 (4)
C5—C4—C3119.9 (4)
C7—C2—C3—C42.4 (7)N1—C9—C10—C11179.9 (4)
C1—C2—C3—C4177.7 (4)C9—C10—C11—C121.1 (7)
C2—C3—C4—C52.1 (7)C10—C11—C12—C130.8 (7)
C3—C4—C5—C60.5 (7)C10—C11—C12—N2179.8 (4)
C3—C4—C5—C8178.9 (4)O2—N2—C12—C13172.0 (4)
C4—C5—C6—C70.8 (6)O3—N2—C12—C135.9 (7)
C8—C5—C6—C7179.8 (4)O2—N2—C12—C117.0 (7)
C3—C2—C7—C61.0 (6)O3—N2—C12—C11175.1 (5)
C1—C2—C7—C6179.0 (4)C11—C12—C13—C140.0 (6)
C5—C6—C7—C20.6 (7)N2—C12—C13—C14179.0 (4)
C9—N1—C8—O10.3 (4)C12—C13—C14—O1179.4 (4)
C9—N1—C8—C5179.6 (4)C12—C13—C14—C90.6 (6)
C14—O1—C8—N10.7 (4)C8—O1—C14—C13179.2 (4)
C14—O1—C8—C5179.2 (3)C8—O1—C14—C90.8 (4)
C6—C5—C8—N1174.5 (4)C10—C9—C14—C130.3 (6)
C4—C5—C8—N16.1 (7)N1—C9—C14—C13179.3 (3)
C6—C5—C8—O15.6 (6)C10—C9—C14—O1179.7 (3)
C4—C5—C8—O1173.8 (4)N1—C9—C14—O10.7 (4)
C8—N1—C9—C140.2 (4)C4—C5—C8—N16.1 (7)
C8—N1—C9—C10179.8 (4)C4—C5—C8—O1173.8 (4)
C14—C9—C10—C110.5 (6)C11—C12—N2—O3175.1 (5)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C10—H10···O2i0.932.613.502 (6)160
C1—H1B···O2ii0.962.803.143 (5)102
Symmetry codes: (i) x+1/2, y, z1/2; (ii) x1/2, y+1/2, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C10—H10···O2i0.932.613.502 (6)160.0
C1—H1B···O2ii0.962.803.143 (5)102.2
Symmetry codes: (i) x+1/2, y, z1/2; (ii) x1/2, y+1/2, z.
Acknowledgements top

The authors thank the Centro Interdipartimentale di Metodologie Chimico-Fisiche, Università degli Studi di Napoli "Federico II", for support.

references
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