Buy article online - an online subscription or single-article purchase is required to access this article.
Download citation
Download citation
link to html
In the title compound, C8H5Br2NO4, the endocyclic angles of the ring deviate significantly from the ideal value of 120°. The substituents deviate from the plane of the ring, with large twist angles for the aldehyde, nitro and methoxy groups. The geometry of the mol­ecule in the crystal is compared with that of the isolated mol­ecule, as given by a self-consistent field molecular-orbital Hartree-Fock calculation. Only weak hydrogen bonds of the C-H...Br and C-H...O types are present in the crystal structure.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100012853/sk1420sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270100012853/sk1420Isup2.hkl
Contains datablock I

CCDC reference: 156181

Comment top

The title compound, (I), was synthesized as a precursor for the synthesis of meso-aryl-substituted porphyrins which are intermediates in the preparation of metalloporphyrins for oxidation catalysis. Hodgson & Beard (1931) studied the reaction of nitric acid with 2,4,6-tribromo-3-hydroxybenzaldehyde and found that substitution of the Br atom by the nitro group occurs at position 6, although the reaction seems equally possible at position 4. We followed the conditions described by Hodgson & Beard and confirmed by X-ray diffraction that the substitution occurs on bromine at position 6. The X-ray study was carried out on a methoxy derivative which gave better crystals than the corresponding hydroxyl compound. \sch

The benzene ring in (I) is planar to within 0.01 Å and the average aromatic C—C distance is 1.387 (8) Å. Bond distances within the ring range from 1.363 (7) to 1.404 (7) Å, the two shortest distances being those adjacent to the unsubstituted C atom. The internal angles of the ring deviate significantly from the ideal value of 120° by as much as 4.2 (4)°, although they add up to exactly 720°, as expected for an aromatic unpuckered ring. The endocyclic angles ipso to the Br atoms and to the nitro group are larger than 120°, whereas those ipso to the unsubstituted C atom and to the aldehyde and methoxy groups are smaller than the ideal value. This is the expected trend due to the σ-inductive electron-withdrawing effect of the substituents on the ring, particularly those of the NO2 group and the Br atoms (Domenicano et al., 1975a,b; Domenicano & Murray-Rust, 1979). According to these authors, the overall deviation of the endocyclic angles from 120° can be calculated, within a good approximation, as a linear combination of the individual effects of each substituent. The average deviation of the angles ipso (α), ortho (β), meta (γ) and para (δ) of mono-substituted aromatic compounds have been estimated for a number of substituents, including the nitro and methoxy groups, using linear regression upon a selection of reliable crystal data (Domenicano & Murray-Rust, 1979). To our knowledge, a similar calculation of the average distortions induced by aldehyde or bromine substituents has not yet been reported.

The rather short aldehyde C7O1 distance [1.196 (6) Å] is consistent with the fact that the O1 atom is not strongly involved in hydrogen bonding (see below). The methoxy group is twisted around the O4—Caryl bond by 77.5 (7)°. Bond distances and angles are typical of this functional group (Allen et al., 1987). The two Br atoms are significantly tilted out of the least-squares plane, Br1 by −0.121 (6) and Br2 by 0.116 (7) Å. The N1 and O4 atoms of the nitro and methoxy groups also deviate from the plane of the ring, although by smaller distances [N1 0.033 (8) and O4 0.058 (7) Å]. Both the aldehyde and nitro groups are twisted around the single bonds C1—C7 and C6—N1, respectively, probably as a result of molecular overcrowding at the C1 position. The twist angles of the aldehyde and nitro groups are 58.5 (7) and 17.9 (7)°, respectively.

In order to gain a better insight into the electronic and steric factors determining the geometry of the molecule, we have performed an ab initio self-consistent field molecular-orbital (SCF-MO) Hartree-Fock calculation, using the quantum-mechanical package GAMESS (Schmidt et al., 1993). A good quality 6–31 G(d,p) basis set was chosen for the C, N, O and H atoms. For the Br atom the 'double zeta' basis set (14 s,11p,5 d)/[6 s,4p,1 d] of Binning & Curtiss (1990) was chosen. The equilibrium geometry of the isolated molecule was located starting from the X-ray geometry without imposing any symmetry constraint. Tight conditions were applied for convergence of the SCF cycles and for location of the equilibrium geometry (Δρ at the end of the SCF cycle = 10−6 bohr−1; maximum gradient at the end of geometry optimization = 10−5 hartree bohr−1 or hartree rad−1).

The calculated equilibrium geometry reproduces well the observed geometric features of the ring, in particular the distortions of the endocyclic bond angles. The observed and calculated deviations, respectively, of the endocyclic angles from the ideal value of 120° are: C1 − 4.2 (4) and −2.9, C2 2.7 (4) and 1.91, C3 − 2.5 (4) and −1.4, C4 1.5 (4) and 0.8, C5 − 1.4 (4) and −1.1, and C6 3.9 (4) and 2.6°. In all cases the correct sign of the deviation is reproduced, although the absolute values of the calculated deviations are always smaller than observed. The calculated twist angles for the aldehyde and nitro groups compare well with the the observed values. The largest difference between the calculated geometry of the free molecule and that measured in the crystal concerns the twist angle of the methoxy group. The equilibrium position calculated for this group corresponds to a symmetrical position with respect to the two Br atoms, with a C8—O4—C3—C4 torsion angle of 90°. Thus, the large deviation of the methoxy group from the symmetric position [C8—O4—C3—C4? 77.5 (7)°] and the slight bending out of the plane of the ring appear to be due to intermolecular interactions involving the methoxy group.

There are no classical hydrogen bonds in the structure, due to the fact that the molecule lacks a strong hydrogen-bond donor. However, it is worth mentioning a possible C—H···O intermolecular interaction [C7···O1i 3.187 (6) Å; symmetry code: (i) x − 1, y, z] bridging the aldehyde groups of two neighbouring molecules. One H atom of the methyl group (H8A) appears to be involved in a weak intramolecular interaction [C8···Br2 3.406 Å] and another H atom of the same group (H8B) is favourably positioned to interact with the aldehyde group of a neighbouring molecule.

Experimental top

A sample of 2,4-dibromo-3-hydroxy-6-nitrobenzaldehyde (2.5 g) was dissolved in acetone (25 ml), and potassium carbonate (1.6 g) and dimethylsulfate (0.81 ml) were added. The mixture was refluxed for 4 h. After evaporation of the solvent the residue was treated with dichloromethane. The organic extracts were washed and dried (Na2SO4). Evaporation of the solvent and recrystallization (water/ethanol) gave 1.7 g (yield 65%) of brown crystals of (I) (m.p. 384 K). 1H NMR (300 MHz, CDCl3/DMSO-d6, δ, p.p.m.): 10.2 (s, 1H), 8.30 (s, 1H), 4.0 (s, 3H). Elemental analysis, calculated for C8H5O4NBr2: C 28.4, H 1.49, N 4.13%; found: C 28.1, H 1.43, N 3.89%.

Refinement top

The methyl group was refined as a rotating rigid group using the AFIX 137 instruction of SHELXL97 (Sheldrick, 1997). All other H atoms were placed at calculated positions and refined as riding using the SHELXL97 defaults. Examination of the crystal structure with PLATON (Spek, 1995) showed that there are no solvent-accessible voids in the crystal lattice.

Computing details top

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: HELENA (Spek, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97; molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. ORTEPII (Johnson, 1976) plot of (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
2,4-dibromo-3-methoxy-6-nitrobenzaldehyde top
Crystal data top
C8H5Br2NO4Dx = 2.180 Mg m3
Mr = 338.95Melting point: 384 K
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
a = 4.3048 (10) ÅCell parameters from 25 reflections
b = 18.108 (3) Åθ = 9.3–15.8°
c = 13.3152 (17) ŵ = 7.84 mm1
β = 95.847 (13)°T = 293 K
V = 1032.5 (3) Å3Plate, colourless
Z = 40.44 × 0.22 × 0.17 mm
F(000) = 648
Data collection top
Enraf-Nonius CAD-4
diffractometer
1238 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.043
Graphite monochromatorθmax = 27.5°, θmin = 3.1°
profile data from ω–2θ scansh = 05
Absorption correction: ψ-scan
(North et al., 1968)
k = 023
Tmin = 0.486, Tmax = 0.955l = 1715
2524 measured reflections3 standard reflections every 180 min
2255 independent reflections intensity decay: 4.7%
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)] = 0.035Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.099H-atom parameters constrained
S = 0.98 w = 1/[σ2(Fo2) + (0.0436P)2 + 1.392P]
where P = (Fo2 + 2Fc2)/3
2255 reflections(Δ/σ)max < 0.001
137 parametersΔρmax = 0.43 e Å3
0 restraintsΔρmin = 0.58 e Å3
Crystal data top
C8H5Br2NO4V = 1032.5 (3) Å3
Mr = 338.95Z = 4
Monoclinic, P21/nMo Kα radiation
a = 4.3048 (10) ŵ = 7.84 mm1
b = 18.108 (3) ÅT = 293 K
c = 13.3152 (17) Å0.44 × 0.22 × 0.17 mm
β = 95.847 (13)°
Data collection top
Enraf-Nonius CAD-4
diffractometer
1238 reflections with I > 2σ(I)
Absorption correction: ψ-scan
(North et al., 1968)
Rint = 0.043
Tmin = 0.486, Tmax = 0.9553 standard reflections every 180 min
2524 measured reflections intensity decay: 4.7%
2255 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0350 restraints
wR(F2) = 0.099H-atom parameters constrained
S = 0.98Δρmax = 0.43 e Å3
2255 reflectionsΔρmin = 0.58 e Å3
137 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
Br10.35548 (13)0.41099 (3)0.05964 (4)0.0580 (2)
Br20.11415 (16)0.25205 (4)0.37595 (5)0.0764 (2)
O10.4495 (9)0.5668 (2)0.1683 (3)0.0725 (12)
O20.0279 (11)0.5964 (2)0.3504 (4)0.0887 (14)
O30.2975 (11)0.5376 (3)0.4320 (3)0.0831 (13)
O40.1957 (8)0.28069 (19)0.1807 (3)0.0566 (9)
N10.1103 (11)0.5408 (3)0.3706 (3)0.0566 (11)
C10.1137 (11)0.4779 (3)0.2296 (3)0.0410 (11)
C20.1789 (10)0.4115 (3)0.1844 (3)0.0393 (10)
C30.1095 (11)0.3429 (3)0.2252 (4)0.0410 (11)
C40.0362 (12)0.3428 (3)0.3149 (4)0.0490 (13)
C50.1129 (11)0.4072 (3)0.3600 (3)0.0495 (12)
H50.21520.40640.41830.059*
C60.0364 (11)0.4724 (3)0.3179 (4)0.0448 (12)
C70.1899 (13)0.5503 (3)0.1842 (4)0.0531 (13)
H70.02920.58380.16760.064*
C80.0426 (14)0.2390 (3)0.1242 (5)0.0749 (18)
H8A0.21970.23470.16220.112*
H8B0.03530.19070.11090.112*
H8C0.10410.26370.06150.112*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Br10.0590 (3)0.0597 (4)0.0588 (3)0.0008 (3)0.0234 (2)0.0022 (3)
Br20.0922 (5)0.0586 (4)0.0783 (4)0.0171 (3)0.0079 (3)0.0285 (3)
O10.057 (2)0.052 (2)0.111 (3)0.009 (2)0.022 (2)0.011 (2)
O20.083 (3)0.055 (3)0.131 (4)0.010 (3)0.027 (3)0.025 (3)
O30.099 (3)0.082 (3)0.073 (3)0.012 (3)0.029 (3)0.013 (2)
O40.051 (2)0.0405 (19)0.080 (3)0.0027 (18)0.0135 (19)0.0077 (19)
N10.052 (3)0.056 (3)0.061 (3)0.000 (2)0.002 (2)0.007 (2)
C10.037 (3)0.038 (3)0.048 (3)0.001 (2)0.002 (2)0.006 (2)
C20.033 (2)0.042 (3)0.044 (2)0.002 (2)0.0070 (18)0.003 (2)
C30.032 (2)0.038 (3)0.052 (3)0.001 (2)0.002 (2)0.003 (2)
C40.047 (3)0.047 (3)0.052 (3)0.009 (2)0.002 (2)0.014 (2)
C50.056 (3)0.051 (3)0.042 (3)0.010 (3)0.008 (2)0.002 (2)
C60.038 (3)0.049 (3)0.047 (3)0.002 (2)0.002 (2)0.005 (2)
C70.047 (3)0.044 (3)0.068 (4)0.003 (3)0.005 (3)0.007 (3)
C80.055 (4)0.063 (4)0.106 (5)0.003 (3)0.006 (3)0.032 (4)
Geometric parameters (Å, º) top
Br1—C21.896 (4)C1—C71.495 (7)
Br2—C41.879 (5)C2—C31.402 (6)
O1—C71.196 (6)C3—C41.404 (7)
O2—N11.214 (6)C4—C51.367 (7)
O3—N11.207 (6)C5—C61.363 (7)
O4—C31.342 (6)C5—H50.9300
O4—C81.425 (7)C7—H70.9300
N1—C61.473 (7)C8—H8A0.9600
C1—C21.386 (6)C8—H8B0.9600
C1—C61.401 (6)C8—H8C0.9600
C3—O4—C8117.4 (4)C6—C5—C4118.6 (4)
O3—N1—O2124.4 (5)C6—C5—H5120.7
O3—N1—C6118.3 (5)C4—C5—H5120.7
O2—N1—C6117.2 (5)C5—C6—C1123.9 (5)
C2—C1—C6115.8 (4)C5—C6—N1117.4 (4)
C2—C1—C7121.5 (4)C1—C6—N1118.7 (5)
C6—C1—C7122.7 (5)O1—C7—C1122.6 (5)
C1—C2—C3122.7 (4)O1—C7—H7118.7
C1—C2—Br1120.2 (3)C1—C7—H7118.7
C3—C2—Br1117.1 (3)O4—C8—H8A109.5
O4—C3—C2119.5 (4)O4—C8—H8B109.5
O4—C3—C4122.9 (4)H8A—C8—H8B109.5
C2—C3—C4117.5 (4)O4—C8—H8C109.5
C5—C4—C3121.5 (4)H8A—C8—H8C109.5
C5—C4—Br2119.6 (4)H8B—C8—H8C109.5
C3—C4—Br2118.9 (4)
C6—C1—C2—C32.0 (6)C3—C4—C5—C62.0 (7)
C7—C1—C2—C3179.9 (5)Br2—C4—C5—C6175.9 (4)
C6—C1—C2—Br1175.7 (3)C4—C5—C6—C10.9 (7)
C7—C1—C2—Br12.2 (6)C4—C5—C6—N1177.5 (4)
C8—O4—C3—C2105.6 (6)C2—C1—C6—C51.1 (7)
C8—O4—C3—C477.5 (7)C7—C1—C6—C5178.9 (5)
C1—C2—C3—O4176.1 (4)C2—C1—C6—N1179.4 (4)
Br1—C2—C3—O46.2 (6)C7—C1—C6—N12.7 (7)
C1—C2—C3—C41.0 (7)O3—N1—C6—C517.9 (7)
Br1—C2—C3—C4176.8 (3)O2—N1—C6—C5160.6 (5)
O4—C3—C4—C5178.1 (5)O3—N1—C6—C1163.6 (5)
C2—C3—C4—C51.1 (7)O2—N1—C6—C117.9 (7)
O4—C3—C4—Br20.2 (7)C2—C1—C7—O158.5 (7)
C2—C3—C4—Br2176.8 (3)C6—C1—C7—O1123.7 (6)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C7—H7···O1i0.932.523.187 (6)129
C8—H8A···Br20.962.853.406 (7)118
C8—H8B···O2ii0.962.553.397 (8)147
Symmetry codes: (i) x1, y, z; (ii) x+1/2, y1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaC8H5Br2NO4
Mr338.95
Crystal system, space groupMonoclinic, P21/n
Temperature (K)293
a, b, c (Å)4.3048 (10), 18.108 (3), 13.3152 (17)
β (°) 95.847 (13)
V3)1032.5 (3)
Z4
Radiation typeMo Kα
µ (mm1)7.84
Crystal size (mm)0.44 × 0.22 × 0.17
Data collection
DiffractometerEnraf-Nonius CAD-4
diffractometer
Absorption correctionψ-scan
(North et al., 1968)
Tmin, Tmax0.486, 0.955
No. of measured, independent and
observed [I > 2σ(I)] reflections
2524, 2255, 1238
Rint0.043
(sin θ/λ)max1)0.649
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.035, 0.099, 0.98
No. of reflections2255
No. of parameters137
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.43, 0.58

Computer programs: CAD-4 Software (Enraf-Nonius, 1989), CAD-4 Software, HELENA (Spek, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97, ORTEPII (Johnson, 1976).

Selected geometric parameters (Å, º) top
C1—C21.386 (6)C4—C51.367 (7)
C2—C31.402 (6)C5—C61.363 (7)
C3—C41.404 (7)
C2—C1—C6115.8 (4)C5—C4—C3121.5 (4)
C1—C2—C3122.7 (4)C6—C5—C4118.6 (4)
C2—C3—C4117.5 (4)C5—C6—C1123.9 (5)
C8—O4—C3—C477.5 (7)C2—C1—C7—O158.5 (7)
O3—N1—C6—C517.9 (7)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C7—H7···O1i0.932.523.187 (6)129.3
C8—H8A···Br20.962.853.406 (7)117.5
C8—H8B···O2ii0.962.553.397 (8)146.8
Symmetry codes: (i) x1, y, z; (ii) x+1/2, y1/2, z+1/2.
 

Subscribe to Acta Crystallographica Section C: Structural Chemistry

The full text of this article is available to subscribers to the journal.

If you have already registered and are using a computer listed in your registration details, please email support@iucr.org for assistance.

Buy online

You may purchase this article in PDF and/or HTML formats. For purchasers in the European Community who do not have a VAT number, VAT will be added at the local rate. Payments to the IUCr are handled by WorldPay, who will accept payment by credit card in several currencies. To purchase the article, please complete the form below (fields marked * are required), and then click on `Continue'.
E-mail address* 
Repeat e-mail address* 
(for error checking) 

Format*   PDF (US $40)
   HTML (US $40)
   PDF+HTML (US $50)
In order for VAT to be shown for your country javascript needs to be enabled.

VAT number 
(non-UK EC countries only) 
Country* 
 

Terms and conditions of use
Contact us

Follow Acta Cryst. C
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds