1,4-Bis(1,1-dimethyl­prop­yl)-2,5-dimeth­oxy­benzene

Abstract

The title compound, C₁₈H₃₀O₂, was prepared by Friedel–Crafts alkyl­ation of 1,4-dimeth­oxy­benzene with 2-methyl-2-butanol. The complete mol­ecule is generated by the application of a crystallographic centre of inversion. The two meth­oxy groups are oriented in the same plane of the aromatic ring [C—C—O—C torsion angle = 9.14 (16)°]. While one methyl group of the tert-pentyl substituent is coplanar with the benzene ring [C—C—C—C = 0.45 (15)°] and lies towards the less-hindered H atom, the other methyl and ethyl groups are directed to either side of the benzene ring [C—C—C—C torsion angles = 118.78 (12) and 59.11 (14)°, respectively]. In the crystal, the hydro­phobic mol­ecules pack to form a brick-wall-like architecture.

Related literature

For the synthesis of the title compound, see: Polito et al. (2010 ▶) and for the synthesis of the analogous compound, 1,4-di-tert-butyl-2,5-dimeth­oxy­benzene, see: Williamson et al. (2006 ▶). For the unique crystal growth of 1,4-di-tert-butyl-2,5-dimeth­oxy­benzene, see: Blatchly & Hartshorne (1966 ▶). For the crystal structure of 1,4-di-tert-butyl-2,5-dimeth­oxy­benzene, see: Rosokha & Kochi (2007 ▶).

Experimental

Crystal data

• C₁₈H₃₀O₂

• M _r = 278.42

• Triclinic,

• a = 6.456 (5) Å

• b = 6.551 (5) Å

• c = 10.800 (5) Å

• α = 93.120 (5)°

• β = 105.950 (5)°

• γ = 108.460 (5)°

• V = 411.5 (5) ų

• Z = 1

• Mo Kα radiation

• μ = 0.07 mm⁻¹

• T = 90 K

• 0.4 × 0.2 × 0.1 mm

Data collection

• Bruker APEXII CCD area-detector diffractometer

• Absorption correction: empirical (using intensity measurements) (SADABS; Bruker, 2009 ▶) T _min = 0.972, T _max = 0.993

• 2473 measured reflections

• 1888 independent reflections

• 1698 reflections with I > 2σ(I)

• R _int = 0.013

Refinement

• R[F ² > 2σ(F ²)] = 0.042

• wR(F ²) = 0.114

• S = 1.10

• 1888 reflections

• 151 parameters

• All H-atom parameters refined

• Δρ_max = 0.40 e Å⁻³

• Δρ_min = −0.22 e Å⁻³

Data collection: APEX2 (Bruker, 2009 ▶); cell refinement: SAINT (Bruker, 2009 ▶); data reduction: SAINT; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: Mercury (Macrae et al., 2008 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶) and publCIF (Westrip, 2010 ▶).

Supplementary Material

Supplementary material file. DOI: 10.1107/S160053681103772X/tk2787Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Comment

Electrophilic aromatic substitution is one of the key reactions in organic chemistry. The Friedel-Crafts alkylation of 1,4-dimethoxybenzene with tert-butyl alcohol is a popular introductory organic laboratory experiment to illustrate the features of electrophilic aromatic substitution (Williamson et al., 2006). The product, 1,4-di-tert-butyl-2,5-dimethoxybenzene, (I), has also been reported to exhibit a dramatic change of shape during crystal growth (Blatchly and Hartshorne, 1966). Recently, a synthesis involving electrophilic aromatic substitution coupled with a Wagner-Meerwein rearrangement using 1,4-dimethoxybenzene with 2-methyl-2-butanol was reported (Polito et al., 2010). However, the product, 1,4-bis(1,1-dimethylpropyl)-2,5-dimethoxybenzene (II), has no dramatic crystal growth behaviour. To obtain the perspectives on both development of sophisticated laboratory activity in organic chemistry and the relationship between crystal growth and molecular structure, the X-ray diffraction analysis of the title compound (II) was performed, and the structural features of (I) and (II) discussed in this article. The crystal structure of (I) has already been reported (Rosokha and Kochi, 2007).

Compound (I) crystallizes in the monoclinic space group P2₁/c. The methoxy groups are inclined at 33.9 (1) ° to the benzene plane. The methyl C—H of the methoxy group points to the adjacent benzene ring in a face-on-edge manner, in which the distance between the methyl carbon and the π-plane is 3.47 (1) Å. The crystal packing exhibits a herringbone structure. Compound (II) crystallizes in the triclinic space group P1 (Fig. 1). The asymmetric unit of (II) contains half a molecule with the complete molecule being generated by a centre of inversion located in the benzene ring. In contrast to (I), the methoxy groups lie on almost the same plane as the benzene ring, where the dihedral angle is 4.9 (1) °. The ethyl chains of two tert-pentyl groups stand to one side of the benzene plane in an anti-orientation, where the dihedral angle is 83.8 (2) °. Since the ethyl chain and methyl group of tert-pentyl group and methoxy group are aggregated by hydrophobic interactions, each molecule is closely arranged in the brick-wall fashion (Fig. 2). Compared to (II) the packing mode of (I) seems to be relatively loose, resulting the expression of dynamic crystal growth of (I).

Experimental

In a 50-ml Erlenmeyer flask were placed 690 mg (5 mmol) of 1,4-dimethoxybenzene, 1.3 g (1.5 mmol) of 2-methyl-2-butanol, and 1.5 ml of glacial acetic acid. The Erlenmeyer flask was immersed in an ice-water bath to cool the solution below 278 K. Concentrated sulfuric acid (5 ml) was added dropwise into the vigorously stirred reaction mixture so as not to exceed the temperature of 283 K. When all the sulfuric acid was added, the mixture was stirred at room temperature for 10 minutes. The Erlenmeyer flask was immersed again in an ice-water bath, and then a sufficient amount of ice-cold water was added into the reaction mixture to quench the reaction and isolate the product. The white solid was filtered off on a small Büchner funnel and washed with a small amount of ice-cold ethanol. Single crystals were obtained by recrystallization from its ethanol solution; M.pt. 382–383 K. ¹H NMR (500 MHz, CDCl₃):δ 6.72 (s, 2 H), 3.76 (s, 6 H), 1.77 (q, 4 H), 1.29 (s, 12 H), 0.62 (q, 6 H) p.p.m. IR (KBr): 2962, 2933, 2868, 1506, 1481, 1392, 1369, 1209, 1128, 1041, 865 cm^-1. APCI-MS: m/z [M—H]⁺ = 277.21621.

Refinement

All H atoms were found in a difference Fourier map and refined isotropically.

Figures

Fig. 1.

The molecular structure of the title compound, showing the atom-numbering scheme and displacement ellipsoids at the 50% probability level for non-H atoms. Atoms marked with i are at the symmetry positions 1 - x, 1 - y, 1 - z.

Fig. 2.

The crystal packing of the title compound showing the brick-wall packing arrangement. All H atoms are omitted for clarity.

Crystal data

C18H30O2	Z = 1
Mr = 278.42	F(000) = 154
Triclinic, P1	Dx = 1.123 Mg m−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71069 Å
a = 6.456 (5) Å	Cell parameters from 1654 reflections
b = 6.551 (5) Å	θ = 3.3–28.8°
c = 10.800 (5) Å	µ = 0.07 mm−1
α = 93.120 (5)°	T = 90 K
β = 105.950 (5)°	Plate, colourless
γ = 108.460 (5)°	0.4 × 0.2 × 0.1 mm
V = 411.5 (5) Å3

Data collection

Bruker APEXII CCD area-detector diffractometer	1888 independent reflections
Radiation source: fine-focus sealed tube	1698 reflections with I > 2σ(I)
graphite	Rint = 0.013
Detector resolution: 8.333 pixels mm-1	θmax = 29.0°, θmin = 2.0°
φ and ω scan	h = −8→5
Absorption correction: empirical (using intensity measurements) (SADABS; Bruker, 2009)'	k = −8→8
Tmin = 0.972, Tmax = 0.993	l = −12→14
2473 measured reflections

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.114	All H-atom parameters refined
S = 1.10	w = 1/[σ2(Fo2) + (0.0566P)2 + 0.1363P] where P = (Fo2 + 2Fc2)/3
1888 reflections	(Δ/σ)max < 0.001
151 parameters	Δρmax = 0.40 e Å−3
0 restraints	Δρmin = −0.22 e Å−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.66045 (17)	0.40800 (16)	0.56010 (10)	0.0142 (2)
C2	0.54020 (18)	0.34722 (16)	0.42749 (10)	0.0146 (2)
C3	0.37620 (17)	0.43475 (16)	0.36311 (10)	0.0134 (2)
C4	0.24450 (18)	0.36052 (16)	0.21713 (10)	0.0149 (2)
C5	0.28316 (19)	0.55446 (18)	0.13993 (10)	0.0186 (2)
C6	0.5309 (2)	0.7013 (2)	0.16805 (13)	0.0273 (3)
C7	0.3162 (2)	0.18507 (18)	0.15790 (11)	0.0199 (3)
C8	−0.01503 (19)	0.25829 (19)	0.19763 (11)	0.0203 (3)
C9	0.8811 (2)	0.17879 (18)	0.54390 (11)	0.0191 (2)
O1	0.81796 (14)	0.31572 (13)	0.62220 (7)	0.0203 (2)
H2	0.574 (3)	0.240 (2)	0.3790 (14)	0.025 (4)*
H5A	0.215 (3)	0.492 (2)	0.0462 (15)	0.023 (4)*
H5B	0.196 (2)	0.646 (2)	0.1572 (14)	0.021 (3)*
H6A	0.599 (3)	0.782 (3)	0.2639 (17)	0.036 (4)*
H6B	0.635 (3)	0.615 (3)	0.1542 (17)	0.037 (4)*
H6C	0.544 (3)	0.819 (3)	0.1069 (16)	0.034 (4)*
H7A	0.226 (3)	0.138 (2)	0.0662 (15)	0.025 (4)*
H7B	0.479 (3)	0.238 (3)	0.1626 (16)	0.030 (4)*
H7C	0.286 (2)	0.050 (2)	0.2014 (14)	0.023 (3)*
H8A	−0.073 (3)	0.360 (2)	0.2338 (14)	0.021 (3)*
H8B	−0.046 (3)	0.123 (3)	0.2390 (15)	0.028 (4)*
H8C	−0.097 (3)	0.216 (2)	0.1031 (15)	0.024 (4)*
H9A	0.744 (3)	0.043 (2)	0.5000 (14)	0.024 (4)*
H9B	1.000 (3)	0.144 (2)	0.6036 (15)	0.027 (4)*
H9C	0.940 (2)	0.256 (2)	0.4774 (14)	0.021 (3)*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
C1	0.0147 (5)	0.0146 (5)	0.0137 (5)	0.0060 (4)	0.0038 (4)	0.0032 (4)
C2	0.0169 (5)	0.0136 (5)	0.0134 (5)	0.0052 (4)	0.0052 (4)	0.0005 (4)
C3	0.0140 (5)	0.0128 (5)	0.0117 (5)	0.0025 (4)	0.0039 (4)	0.0012 (3)
C4	0.0161 (5)	0.0155 (5)	0.0113 (5)	0.0049 (4)	0.0027 (4)	0.0001 (4)
C5	0.0227 (6)	0.0191 (5)	0.0127 (5)	0.0061 (4)	0.0046 (4)	0.0025 (4)
C6	0.0246 (6)	0.0294 (6)	0.0248 (6)	0.0034 (5)	0.0089 (5)	0.0072 (5)
C7	0.0241 (6)	0.0199 (5)	0.0138 (5)	0.0087 (4)	0.0024 (4)	−0.0029 (4)
C8	0.0168 (5)	0.0222 (6)	0.0166 (5)	0.0028 (4)	0.0020 (4)	0.0005 (4)
C9	0.0215 (5)	0.0214 (5)	0.0179 (5)	0.0129 (4)	0.0056 (4)	0.0021 (4)
O1	0.0255 (4)	0.0258 (4)	0.0137 (4)	0.0173 (3)	0.0028 (3)	0.0007 (3)

Geometric parameters (Å, °)

C1—O1	1.3812 (14)	C6—H6A	1.043 (17)
C1—C2	1.3941 (15)	C6—H6B	1.037 (17)
C1—C3i	1.4051 (15)	C6—H6C	1.038 (18)
C2—C3	1.3988 (16)	C7—H7A	0.976 (15)
C2—H2	0.963 (15)	C7—H7B	0.984 (17)
C3—C1i	1.4051 (15)	C7—H7C	1.012 (16)
C3—C4	1.5371 (15)	C8—H8A	0.973 (15)
C4—C7	1.5376 (16)	C8—H8B	1.003 (17)
C4—C8	1.5428 (19)	C8—H8C	0.990 (15)
C4—C5	1.5494 (17)	C9—O1	1.4229 (14)
C5—C6	1.5172 (19)	C9—H9A	1.014 (16)
C5—H5A	0.991 (15)	C9—H9B	0.955 (16)
C5—H5B	0.985 (15)	C9—H9C	0.992 (15)
O1—C1—C2	121.95 (10)	H6A—C6—H6B	107.7 (13)
O1—C1—C3i	117.05 (9)	C5—C6—H6C	110.9 (9)
C2—C1—C3i	121.00 (10)	H6A—C6—H6C	107.8 (13)
C1—C2—C3	122.99 (10)	H6B—C6—H6C	107.0 (13)
C1—C2—H2	117.7 (9)	C4—C7—H7A	109.6 (9)
C3—C2—H2	119.3 (9)	C4—C7—H7B	112.6 (9)
C2—C3—C1i	116.02 (10)	H7A—C7—H7B	107.7 (13)
C2—C3—C4	121.35 (9)	C4—C7—H7C	112.1 (8)
C1i—C3—C4	122.63 (9)	H7A—C7—H7C	106.2 (12)
C3—C4—C7	111.63 (9)	H7B—C7—H7C	108.4 (12)
C3—C4—C8	109.87 (9)	C4—C8—H8A	111.4 (9)
C7—C4—C8	106.83 (9)	C4—C8—H8B	109.7 (9)
C3—C4—C5	111.30 (9)	H8A—C8—H8B	110.2 (13)
C7—C4—C5	108.72 (10)	C4—C8—H8C	108.6 (9)
C8—C4—C5	108.33 (9)	H8A—C8—H8C	108.9 (12)
C6—C5—C4	115.63 (10)	H8B—C8—H8C	107.9 (13)
C6—C5—H5A	110.5 (9)	O1—C9—H9A	109.7 (9)
C4—C5—H5A	106.6 (9)	O1—C9—H9B	104.8 (9)
C6—C5—H5B	107.9 (9)	H9A—C9—H9B	111.0 (12)
C4—C5—H5B	109.7 (9)	O1—C9—H9C	111.1 (8)
H5A—C5—H5B	106.2 (12)	H9A—C9—H9C	110.1 (12)
C5—C6—H6A	111.1 (10)	H9B—C9—H9C	110.1 (13)
C5—C6—H6B	112.1 (10)	C1—O1—C9	118.00 (9)

Symmetry codes: (i) −x+1, −y+1, −z+1.