Predicted and experimental crystal structures of ethyl-tert-butyl ether

Possible crystal structures of ethyl-tert-butyl ether (ETBE) were predicted by global lattice-energy minimizations using the force-field approach. 33 structures were found within an energy range of 2 kJ mol^-1 above the global minimum. Low-temperature crystallization experiments were carried out at 80-160 K. The crystal structure was determined from X-ray powder data. ETBE crystallizes in C2/m, Z = 4, with molecules on mirror planes. The ETBE molecule adopts a trans conformation with a (CH₃)₃C-O-C-C torsion angle of 180°. The experimental structure corresponds with high accuracy to the predicted structure with energy rank 2, which has an energy of 0.54 kJ mol^-1 above the global minimum and is the most dense low-energy structure. In some crystallization experiments a second polymorph was observed, but the quality of the powder data did not allow the determination of the crystal structure. Possibilities and limitations are discussed for solving crystal structures from powder diffraction data by real-space methods and lattice-energy minimizations.

Computing details

Data collection: STOE WinXPOW (STOE & Cie GmbH, 2005); cell refinement: TOPAS Academic (Coelho, 2007); data reduction: DASH (David et al., 2006); program(s) used to solve structure: DASH (David et al., 2006); program(s) used to refine structure: TOPAS Academic (Coelho, 2007); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2009).

Figures

2-ethoxy-2-methylpropane

Crystal data

C6H14O	none
Mr = 102.17	Dx = 0.971 Mg m^−3
Monoclinic, C2/m	Cu Kα1 radiation, λ = 1.54056 Å
a = 14.7170 (3) Å	µ = 0.49 mm^−1
b = 7.76462 (17) Å	T = 123 K
c = 6.22813 (16) Å	Particle morphology: no specific habit
β = 101.0148 (15)°	colourless
V = 698.59 (3) Å^3	cylinder, 10 × 0.7 mm
Z = 4	Specimen preparation: Prepared at 123 K
F(000) = 232.0

Data collection

STOE Stadi-P diffractometer	Data collection mode: transmission
Primary focussing, Ge 111 monochromator	Scan method: step
Specimen mounting: glass capillary	2θmin = 5.0°, 2θmax = 69.99°, 2θstep = 0.01°

Refinement

Least-squares matrix: full with fixed elements per cycle	114 parameters
Rp = 0.034	32 restraints
Rwp = 0.046	0 constraints
Rexp = 0.017	All H-atom parameters refined
χ^2 = 7.366	Weighting scheme based on measured s.u.'s
6500 data points	(Δ/σ)max = 0.001
Excluded region(s): none	Background function: Chebyshev with 50 terms
Profile function: modified Thompson-Cox-Hastings pseudo-Voigt(Young, 1993)	Preferred orientation correction: Correction based on March (1932)

Special details

Experimental. specimen was rotated, amorphous SiO₂ in glass capillary

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O4	0.26110 (11)	0.00000	0.3763 (3)	0.0337*
C1	0.14543 (12)	0.00000	0.5910 (3)	0.0337*
C2	0.16127 (12)	0.00000	0.3546 (3)	0.0337*
C3	0.11775 (10)	0.16530 (19)	0.2431 (3)	0.0337*
C5	0.29674 (12)	0.00000	0.1785 (3)	0.0337*
C6	0.40379 (12)	0.00000	0.2339 (3)	0.0337*
H1A	0.0702 (4)	0.00000	0.5947 (14)	0.0405*
H1B	0.1790 (3)	0.1103 (5)	0.6798 (7)	0.0405*
H3A	0.0444 (3)	0.1729 (5)	0.2514 (7)	0.0405*
H3B	0.1531 (3)	0.2799 (6)	0.3186 (8)	0.0405*
H3C	0.1234 (3)	0.1648 (6)	0.0743 (8)	0.0405*
H5A	0.2728 (3)	−0.1122 (5)	0.0794 (8)	0.0405*
H6A	0.4319 (4)	0.00000	0.0828 (12)	0.0405*
H6B	0.4288 (3)	−0.1122 (5)	0.3297 (8)	0.0405*

Geometric parameters (Å, º)

O4—C2	1.450 (2)	C3—H3A	1.092 (5)
O4—C5	1.428 (3)	C3—H3B	1.091 (5)
C1—C2	1.534 (3)	C3—H3C	1.070 (5)
C2—C3	1.5394 (19)	C5—H5A	1.087 (4)
C5—C6	1.547 (3)	C6—H6A	1.098 (7)
C1—H1A	1.112 (6)	C6—H6B	1.080 (4)
C1—H1B	1.086 (4)
C2—O4—C5	116.89 (16)	C2—C3—H3C	109.7 (3)
O4—C2—C1	104.34 (15)	H3A—C3—H3B	109.3 (3)
O4—C2—C3	111.65 (10)	H3A—C3—H3C	108.0 (4)
C1—C2—C3	107.85 (11)	H3B—C3—H3C	107.8 (4)
O4—C5—C6	109.50 (15)	O4—C5—H5A	110.9 (3)
C2—C1—H1A	110.8 (5)	C6—C5—H5A	109.4 (3)
C2—C1—H1B	110.6 (3)	C5—C6—H6A	110.1 (4)
H1A—C1—H1B	110.3 (4)	C5—C6—H6B	110.4 (3)
C2—C3—H3A	110.7 (2)	H6A—C6—H6B	109.2 (3)
C2—C3—H3B	111.3 (3)