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The title compound, C9H10Br2O, is a major product of the radical bromination of 4-methoxy-1,2-di­methyl­benzene. Each Br atom is involved in a close contact with the O atom of a neighbouring mol­ecule, forming a geometry that is suggestive of weak intermolecular O\rightarrowBr charge-transfer interactions.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100019375/bm1445sup1.cif
Contains datablocks II, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270100019375/bm1445IIsup2.hkl
Contains datablock bm1445gf

CCDC reference: 162582

Comment top

There are two recent reports that bromination of 3,4-dimethylmethoxybenzene by excess N-bromosuccinimide under free-radical conditions affords 3,4-bis(bromomethyl)methoxybenzene (I) in >80% yield (Ohkawa et al., 1997; Wang et al., 1997). In our hands, the reported procedure in fact yields 3-methyl-4-(dibromomethyl)methoxybenzene (II) and 3-methyl-4-(bromomethyl)methoxybenzene (III) (Tanzawa et al., 1995) in addition to I, with yields of approximately 30% (I), 25% (II) and 15% (III). The crystal structure of II, a new compound, was undertaken in order to determine unambiguously which of the two methyl groups of the precursor had been doubly brominated.

Interestingly, C10—Br12 [1.983 (4) Å] is substantially longer than C10—Br11 [1.948 (5) Å]. None of the three (dibromomethyl)arenes that have been structured previously exhibit this feature (García et al., 1995; Stanger et al., 1998; Sygula & Rabideau, 1998). It is suggestive that the lengthened C10—Br12 bond in II is almost perpendicular to the plane of the C1–C6 ring [C3—C4—C10—Br12 = 95.1 (4)°], which might conceivably reflect hyperconjugation between the C10—Br12 σ* orbital and the phenyl π system. This would provide a convenient rationale for the lengthened C10—Br12 bond. However, static and energy-minimized AM1 calculations (CambridgeSoft, 1999) have demonstrated that Br12 makes no contribution to the π orbitals of the compound, which appears to rule out this explanation. All other bond lengths and angles within the molecule are unexceptional.

There are three unusually short intermolecular contacts in the lattice. Both Br atoms form a contact with O7 from a neighbouring molecule (Table 1). For both these interactions, the O7···Br#—C10# (# = i, ii; Table 1) angle is close to linear, while the disposition of C—O and O···Br# vectors about O7 forms a distorted tetrahedron [the angles about O7 not in Table 1 are C1—O7—C8 = 116.7 (4) and Br11i···O7···Br12ii = 90.0 (2)°; the average angle about O7 including these intermolecular interactions is hence 108.3 (7)°]. These parameters are suggestive of weak intermolecular charge-transfer interactions between the lone pairs of O7 and the C—Br σ* antibonding orbitals. There is also a close contact between H10 and Br12iii, related by 1 - x, 1 - y, 1 - z, with C10···Br12iii = 3.712 (5) Å, H10···Br12iii = 3.00 Å and C10—H10···Br12iii = 129°. A similar intramolecular C—H···Br interaction is observed in the structure of methyl 2,3-bis(dibromomethyl)benzoate (Stanger et al., 1998). For comparison, the sum of the van der Waals radii of O and Br atoms is 3.35 Å, and of H and Br atoms is 3.15 Å (Pauling, 1960).

There are two intermolecular ππ interactions in the lattice, between molecules related by inversion at 1 - x, 2 - y, 1 - z (interplanar spacing 3.48 Å, centroid offset 3.6 Å); and at -x, 2 - y, 2 - z (interplanar spacing 3.70 Å, centroid offset 3.9 Å). In both these interactions, the stacked rings are strictly coplanar by symmetry, and have relative orientations that are consistent with an electrostatically attractive ππ interaction (Hunter & Sanders, 1990).

Related literature top

For related literature, see: CambridgeSoft (1999); García et al. (1995); Hunter & Sanders (1990); Ohkawa et al. (1997); Pauling (1960); Stanger et al. (1998); Sygula & Rabideau (1998); Tanzawa et al. (1995); Wang et al. (1997).

Experimental top

3,4-Dimethylmethoxybenzene (5.0 g, 36.3 mmol), N-bromosuccinimide (14.4 g, 80 mmol) and benzoylperoxide (0.04 g, 0.2 mmol) were mixed in CCl4 (70 cm3), and the resultant suspension refluxed for 30 min. Following cooling, evaporation of the solvent in vacuo yielded a pale brown oil that contained a mixture of compounds (I), (II) and (III) from thin-layer chromatography and 1H NMR spectroscopy. Compound (II) was separated from the reaction mixture by fractional crystallization of the crude material from 1:1 diethyl ether:hexanes, which yielded moisture-sensitive white microcrystals. Recrystallization from the same solvent mixture yielded small colourless needles. 1H NMR spectrum of (II) (CDCl3, 250 MHz, 293 K): δ 7.76 p.p.m. (d, 8.8 Hz, 1H, Ph H5), 6.88 (s, 1H, CHBr2), 6.80 (dd, 2.8 and 8.8 Hz, 1H, Ph H6), 6.63 (d, 2.8 Hz, 1H, Ph H2), 3.81 (s, 3H, OCH3), 2.42 (s, 3H, CH3).

Refinement top

H atoms were placed in calculated positions and refined using a riding model. The C—H distances employed for the final refinement were 0.95 Å for the aryl H atoms, 0.98 Å for the methyl groups and 1.00 Å for H10.

Computing details top

Data collection: COLLECT (Nonius, 1999); cell refinement: DENZO-SMN (Otwinowski & Minor, 1996); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEX (McArdle, 1995); software used to prepare material for publication: local program.

Figures top
[Figure 1] Fig. 1. Molecular structure of (II) with 50% probability displacement ellipsoids, showing the atom-numbering scheme employed.
3-Methyl-4-(dibromomethyl)methoxybenzene top
Crystal data top
C9H10Br2OZ = 2
Mr = 293.99F(000) = 284
Triclinic, P1Dx = 1.971 Mg m3
a = 7.4692 (5) ÅMo Kα radiation, λ = 0.71073 Å
b = 8.7343 (7) ÅCell parameters from 5761 reflections
c = 8.9090 (7) Åθ = 3.3–27.5°
α = 68.104 (4)°µ = 8.13 mm1
β = 77.038 (4)°T = 150 K
γ = 67.310 (4)°Lath, colourless
V = 495.34 (6) Å30.14 × 0.07 × 0.01 mm
Data collection top
Nonius kappaCCD area detector
diffractometer
2258 independent reflections
Radiation source: fine-focus sealed tube1698 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.061
Detector resolution: 9.091 pixels mm-1θmax = 27.5°, θmin = 3.3°
Area detector scansh = 99
Absorption correction: multi-scan
(SORTAV; Blessing, 1995)
k = 1111
Tmin = 0.396, Tmax = 0.923l = 1011
5761 measured reflections
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)] = 0.045H-atom parameters constrained
wR(F2) = 0.109 w = 1/[σ2(Fo2) + (0.0469P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.01(Δ/σ)max < 0.001
2258 reflectionsΔρmax = 0.68 e Å3
112 parametersΔρmin = 0.77 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.012 (2)
Crystal data top
C9H10Br2Oγ = 67.310 (4)°
Mr = 293.99V = 495.34 (6) Å3
Triclinic, P1Z = 2
a = 7.4692 (5) ÅMo Kα radiation
b = 8.7343 (7) ŵ = 8.13 mm1
c = 8.9090 (7) ÅT = 150 K
α = 68.104 (4)°0.14 × 0.07 × 0.01 mm
β = 77.038 (4)°
Data collection top
Nonius kappaCCD area detector
diffractometer
2258 independent reflections
Absorption correction: multi-scan
(SORTAV; Blessing, 1995)
1698 reflections with I > 2σ(I)
Tmin = 0.396, Tmax = 0.923Rint = 0.061
5761 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0450 restraints
wR(F2) = 0.109H-atom parameters constrained
S = 1.01Δρmax = 0.68 e Å3
2258 reflectionsΔρmin = 0.77 e Å3
112 parameters
Special details top

Experimental. Area detector set at 30 mm from sample with different 2theta offsets. 1 degree phi exposures for chi=0 degree settings. 1 degree omega exposures for chi=90 degree settings. Structure solution was achieved by direct methods using SHELXS97 (Sheldrick, 1990), while least-squares refinement used SHELXL97 (Sheldrick, 1997). No disorder was detected during refinement, and no restraints were applied. All non-H atoms were refined anisotropically,

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.

All the H atoms were located in a Fourier map during refinement. However, these refined poorly when added to the model, giving meaninglessly low thermal parameters and a wide spread of C—H bond lengths and X—C—H (X = H, C, O) angles. Therefore, in the final refinements all H atoms were placed in calculated positions and refined using a riding model.

The lowest residual electron hole of -1.0 e.Å-3 lies 0.8 Å from Br11.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Br110.74279 (7)0.50436 (6)0.72130 (6)0.03332 (19)
Br120.32133 (7)0.50103 (6)0.71270 (6)0.03477 (19)
O70.1048 (4)1.2345 (4)0.8705 (4)0.0278 (7)
C10.2033 (6)1.0870 (6)0.8270 (5)0.0231 (9)
C20.1845 (6)1.1052 (6)0.6676 (5)0.0253 (9)
H20.10881.21450.59980.030*
C30.2769 (6)0.9627 (6)0.6074 (5)0.0230 (9)
C40.3883 (7)0.8040 (6)0.7084 (5)0.0253 (9)
C50.4039 (6)0.7879 (6)0.8682 (5)0.0264 (9)
H50.47910.67910.93690.032*
C60.3115 (7)0.9281 (6)0.9272 (5)0.0255 (9)
H60.32240.91511.03580.031*
C80.1035 (7)1.2182 (7)1.0375 (6)0.0301 (10)
H8A0.03541.33301.05290.045*
H8B0.23791.17451.06540.045*
H8C0.03631.13621.10790.045*
C90.2484 (7)0.9869 (7)0.4367 (5)0.0298 (10)
H9A0.37360.97450.36990.045*
H9B0.15571.10380.39050.045*
H9C0.19750.89810.43860.045*
C100.4860 (6)0.6513 (6)0.6476 (5)0.0258 (9)
H100.50120.69700.52620.031*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Br110.0315 (3)0.0293 (3)0.0317 (3)0.0027 (2)0.00300 (19)0.0094 (2)
Br120.0418 (3)0.0347 (3)0.0358 (3)0.0180 (2)0.0050 (2)0.0194 (2)
O70.0321 (17)0.0253 (17)0.0257 (16)0.0056 (14)0.0044 (13)0.0108 (14)
C10.023 (2)0.025 (2)0.026 (2)0.0106 (19)0.0004 (17)0.0107 (18)
C20.028 (2)0.021 (2)0.025 (2)0.008 (2)0.0066 (18)0.0035 (18)
C30.024 (2)0.026 (2)0.017 (2)0.0095 (19)0.0009 (16)0.0037 (18)
C40.031 (2)0.028 (2)0.018 (2)0.014 (2)0.0007 (17)0.0059 (18)
C50.027 (2)0.027 (2)0.019 (2)0.007 (2)0.0058 (17)0.0014 (18)
C60.030 (2)0.025 (2)0.021 (2)0.009 (2)0.0012 (17)0.0068 (18)
C80.039 (3)0.031 (3)0.028 (2)0.012 (2)0.0024 (19)0.018 (2)
C90.034 (3)0.031 (3)0.023 (2)0.008 (2)0.0049 (18)0.008 (2)
C100.026 (2)0.026 (2)0.022 (2)0.006 (2)0.0016 (17)0.0092 (19)
Geometric parameters (Å, º) top
Br11—C101.948 (5)C5—C61.384 (6)
Br12—C101.983 (4)C5—H50.9500
O7—C11.365 (5)C6—H60.9500
O7—C81.440 (5)C8—H8A0.9800
C1—C61.382 (6)C8—H8B0.9800
C1—C21.402 (6)C8—H8C0.9800
C2—C31.408 (6)C9—H9A0.9800
C3—C41.392 (6)C9—H9B0.9800
C3—C91.508 (6)C9—H9C0.9800
C4—C51.404 (6)C10—H101.0000
C4—C101.488 (6)
C1—O7—C8116.7 (4)O7—C8—H8B109.5
O7—C1—C6125.3 (4)H8A—C8—H8B109.5
O7—C1—C2114.5 (4)O7—C8—H8C109.5
C6—C1—C2120.2 (4)H8A—C8—H8C109.5
C1—C2—C3120.5 (4)H8B—C8—H8C109.5
C4—C3—C2118.9 (4)C3—C9—H9A109.5
C4—C3—C9122.5 (4)C3—C9—H9B109.5
C2—C3—C9118.7 (4)H9A—C9—H9B109.5
C3—C4—C5119.8 (4)C3—C9—H9C109.5
C3—C4—C10119.7 (4)H9A—C9—H9C109.5
C5—C4—C10120.5 (4)H9B—C9—H9C109.5
C6—C5—C4121.1 (4)C4—C10—Br11114.8 (3)
C1—C6—C5119.6 (4)C4—C10—Br12110.3 (3)
C4—C10—Br11114.8 (3)Br11—C10—Br12107.9 (2)
C4—C10—Br12110.3 (3)C4—C10—H10107.9
Br11—C10—Br12107.9 (2)Br11—C10—H10107.9
O7—C8—H8A109.5Br12—C10—H10107.9
C8—O7—C1—C64.5 (6)C3—C4—C5—C60.6 (6)
C8—O7—C1—C2174.1 (4)C10—C4—C5—C6179.1 (4)
O7—C1—C2—C3179.3 (4)O7—C1—C6—C5179.7 (4)
C6—C1—C2—C30.6 (6)C2—C1—C6—C51.1 (6)
C1—C2—C3—C40.5 (6)C4—C5—C6—C10.6 (6)
C1—C2—C3—C9178.5 (4)C3—C4—C10—Br11142.8 (3)
C2—C3—C4—C51.1 (6)C5—C4—C10—Br1138.7 (5)
C9—C3—C4—C5177.8 (4)C3—C4—C10—Br1295.1 (4)
C2—C3—C4—C10179.6 (4)C5—C4—C10—Br1283.4 (4)
C9—C3—C4—C100.7 (6)

Experimental details

Crystal data
Chemical formulaC9H10Br2O
Mr293.99
Crystal system, space groupTriclinic, P1
Temperature (K)150
a, b, c (Å)7.4692 (5), 8.7343 (7), 8.9090 (7)
α, β, γ (°)68.104 (4), 77.038 (4), 67.310 (4)
V3)495.34 (6)
Z2
Radiation typeMo Kα
µ (mm1)8.13
Crystal size (mm)0.14 × 0.07 × 0.01
Data collection
DiffractometerNonius kappaCCD area detector
diffractometer
Absorption correctionMulti-scan
(SORTAV; Blessing, 1995)
Tmin, Tmax0.396, 0.923
No. of measured, independent and
observed [I > 2σ(I)] reflections
5761, 2258, 1698
Rint0.061
(sin θ/λ)max1)0.649
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.045, 0.109, 1.01
No. of reflections2258
No. of parameters112
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.68, 0.77

Computer programs: COLLECT (Nonius, 1999), DENZO-SMN (Otwinowski & Minor, 1996), DENZO-SMN, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), ORTEX (McArdle, 1995), local program.

Table 1. Selected distances (Å) and angles (°) for the close intermolecular O···Br contacts in (II) (# = i, ii). top
InteractionO7···BrO7···Br#—C10#C1—O7···Br#C8—O7···Br#
O7···Br11i2.999 (5)170.3 (3)122.3 (3)112.7 (3)
O7···Br12ii3.075 (5)169.5 (3)110.1 (3)98.1 (3)
Symmetry codes: (i) -1+x, 1+y, z; (ii) x, 1+y, z.
 

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